For many years the determination of a routine lipid profile (total, LDL, and HDL cholesterol and triglycerides) has been done routinely in the clinical laboratory using a blood specimen that is collected in the fasting state. The rationale for such a requirement includes 1) the postprandial changes in lipoprotein composition known to occur, particularly the increases in triglycerides (TG)10 concentration which have a direct relation to the meal fat and carbohydrate content, 2) the clinically significant effects of increased TG (>400 mg/dL; 4.5 mmol/L) on the calculation of LDL cholesterol (LDL-C) when using the Friedewald equation, and 3) the use of fasting samples for lipid measurement in many clinical trials and epidemiological studies on which treatment goals are based. However, because most of each person's lifetime is spent in the postprandial state, the wisdom of collecting a fasting sample to determine future risk of cardiovascular disease has been challenged. In addition, recent evidence has demonstrated that nonfasting TG concentrations are a better predictor of future coronary events compared to fasting TG, in both men and women. The Danish Society for Clinical Biochemistry, in 2009, and the UK National Institute of Clinical Excellence (NICE), in 2014, recommended the use of a nonfasting specimen for the determination of routine lipid profile; both entities acknowledge that in certain situations a fasting sample is required. The European Atherosclerosis Society and the European Federation of Clinical Chemistry and Laboratory Medicine will be making a similar recommendation. In contrast, the 2013 guidelines released by the American College of Cardiology/American Heart Association (ACC/AHA) preferred a fasting specimen for lipid testing. Such inconsistencies in published guidelines will complicate the interpretation of the literature and confound metaanalyses. The decision of whether to use a fasting or nonfasting sample, however, will be driven not only by the strong epidemiologic and clinical evidence and the convenience to clinicians and patients but also by the reliability of the analytical techniques used in the measurement of these analytes. To address this issue, we invited a group of experts consisting of cardiologists, epidemiologists, clinical researchers, and clinical chemists to share their views on this topic.
What is the evidence that fasting samples are better than nonfasting samples for clinical use?
Anthony S. Wierzbicki: Fasting samples are superior for assessment of severe hypertriglyceridemia as they reduce postprandial variation, which is substantial for this lipid fraction, ranging from 20% to 40%. They are also preferred if LDL-C is to be calculated using the Friedewald equation. Recent data from the Very Large Database of Lipids study show that even a mild increase of TG (>220 mg/dL; 2.5 mmol/L) can have a significant impact on calculated LDL-C. This is an important clinical problem as calculated LDL-C underestimates real LDL-C in patients with type 2 diabetes, the metabolic syndrome, or other hypertriglyceridemic states.
Børge G. Nordestgaard: I am not aware of any.
Hubert Vesper: Only a few studies have compared fasting and nonfasting specimens in the context of classification of risk for atherosclerotic cardiovascular diseases (ASCVD) and related health outcomes. Collectively, the findings reported in these studies do not show higher accuracy of ASCVD risk assessment when using fasting samples. ASCVD risk is commonly assessed by measuring total cholesterol (TC), HDL-C, TG, and LDL-C, with LDL-C either calculated using the Friedewald equation or measured using direct homogenous assays. The Friedewald equation is based on the observation that the mass ratio of TG to cholesterol in VLDL is relatively constant in the fasting state. Thus, risk estimations using LDL-C calculated with the Friedewald equation require fasting samples. Use of direct homogenous assays can overcome the limitations associated with the Friedewald equation. However, data suggest that direct homogenous assays can also be affected by feeding to an extent that may affect clinical decisions. Other approaches for ASCVD risk assessment include analytes such as non–HDL-C and apolipoproteins, which appear less affected by recent food intake and therefore may not require a fasting specimen. The choice of using specimens from fasting or nonfasting patients depends on the intended analytes and the ASCVD risk assessment approach used.
Samia Mora: Lipid testing plays a major role in ASCVD risk screening, prediction, and treatment. For cardiovascular risk screening and prediction, there is no convincing evidence that a lipid panel is better when done on a fasting blood sample. In fact, a nonfasting lipid panel may even be better than a fasting panel. In the past decade, several pivotal studies (including the Women's Health Study, the Copenhagen City Heart Study, and the Copenhagen General Population Study) found that nonfasting TG were at least as good, if not better, than fasting TG in predicting future risk of cardiovascular events. Importantly, in a metaanalysis from the Emerging Risk Factors Collaboration that included data from over 300 000 individuals from 68 prospective studies, LDL-C and non—HDL-C were significantly more predictive of cardiovascular events when measured nonfasting. For treatment, most guidelines are emphasizing treating the high-risk patient rather than the high LDL-C value. Even so, several landmark randomized clinical trials of statin therapy [including the Heart Protection Study, ASCOT-LLA (Anglo-Scandinavian Cardiac Outcomes Trial–Lipid Lowering Arm), and the SEARCH (Study of the Effectiveness of Additional Reductions in Cholesterol and Homocysteine) trials] used nonfasting lipid measures for treatment.
Neil J. Stone: It truly depends on the question you ask. If you ask, will a nonfasting specimen suffice to determine global ASCVD risk assessment, the answer is yes. The pooled cohort equations, the Reynolds Risk Score and the QRISK score, for example, only require a TC and HDL-C as lipid inputs. On the other hand, a fasting sample helps greatly in the diagnosis of genetic dyslipidemia and helps determine response to therapy of those with hyperlipidemic pancreatitis.
Moreover, fasting TG are one of the 5 markers for metabolic syndrome, a useful construct in those patients who require lifestyle counseling. Also, in secondary prevention patients prescribed statins, a fasting lipid panel can provide valuable information on adherence to the statin (their LDL-C concentration) and adherence to lifestyle (fasting TG also may be useful here) and on-treatment fasting TG <150 mg/dL (1.7 mmol/L) can indicate a lower risk of recurrent coronary events.
Jacques Genest: None really, from a scientific point of view. The accuracy of the Friedewald formula for the determination of LDL-C has been shown to be very dependent on TG concentrations. However, within a broad range of serum TG values, this calculation is clinically valid.
What are the advantages of using nonfasting samples?
Børge G. Nordestgaard: The most obvious advantage is that it simplifies blood sampling for patients, laboratories, and clinicians and is also likely to improve patient compliance with lipid testing. Certainly, patients are often inconvenienced by having to return on a separate visit for a fasting lipid profile, laboratories are burdened by a large number of patients attending for tests in the morning, and clinicians are burdened by having to review and make decisions on the findings in the lipid profile at a later date.
Anthony S. Wierzbicki: Nonfasting samples are more convenient for the patient and the physician. They can be used to derive non–HDL-C, a measure that is superior to LDL-C for risk assessment as it includes atherogenic TG-rich lipoproteins.
Hubert Vesper: The advantages of collecting nonfasting specimens are typically related to convenience of scheduling patients and concerns related to the accuracy of determining the time to last meal. To obtain fasting specimens, patients are normally scheduled in the morning after an overnight fast or are asked to abstain from eating for at least 8 hours. In routine patient care, the assessment of patient compliance with this request is difficult to perform. Research findings suggest that information on postprandial lipid concentrations can provide valuable information for ASCVD risk assessment that cannot be obtained with fasting samples. However, more data are needed to further validate these findings.
Samia Mora: The main advantage is the practicality of measuring nonfasting lipids, for the patient, the healthcare provider, and the laboratory. Compliance has always been an issue with fasting blood tests, in particular for children or individuals who may not be able to fast. Patients may not know ahead of their appointment that they should have fasted, or they may forget and often expend additional resources to return to a laboratory while fasting, and some may forgo coming back altogether. The healthcare provider or the laboratory then must decide whether to make the patient return another time (which is costly, and which the patient may or may not comply with) or rely on a nonfasting sample.
Neil J. Stone: In my clinic, most important is the convenience factor for those who are seen in the clinic later in the day. It is expensive for patients to return to the medical center or laboratory to get additional testing, especially if a nonfasting specimen will suffice.
Greg Miller: The only advantage is convenience for patients. The practical reality is a large proportion of lipid profiles are likely already performed in the nonfasting condition.
What are the situations for which a fasting sample is required?
Børge G. Nordestgaard: I am not aware of any.
Anthony S. Wierzbicki: Fasting samples are required to determine reproducible TG concentrations in patients with TG in the range of 885–1770 mg/dL (10–20 mmol/L). If the presence of high concentrations is confirmed and confounding by diet or alcohol is excluded, then patients with severe hypertriglyceridemia may require additional TG-directed lipid lowering therapy (fibrate or ω-3 fatty acid) in addition to baseline statins.
Hubert Vesper: Calculations such as the Friedewald equation and risk models that are based on fasting specimens obviously require fasting specimens. Patients with suspected hypertriglyceridemia in nonfasting specimens require retesting using fasting specimens for confirmation. This is consistent with current ASCVD risk assessment guidelines that recommend use of nonfasting specimens for initial assessments.
Samia Mora: It is reasonable to consider nonfasting lipid testing in most individuals who present for a routine clinic visit, with the possible exception of individuals with TG >400–500 mg/dL (4.5–5.7mmol/L), in whom the Friedewald equation for estimating LDL-C may not be accurate. However, even in such individuals with high TG, cardiovascular risk prediction using TC and HDL-C (or non-HDL-C) would still be the standard, as that is what is used in contemporary risk equations. Furthermore, using non-HDL-C or apolipoprotein B (both of which could be measured nonfasting) would be preferable over LDL-C for treatment decisions in these individuals, as they are better reflections of the burden of atherogenic lipoproteins in these individuals compared with LDL-C or TC.
Jacques Genest: The error induced in the Friedewald formula by increased TG may cause an underestimation of LDL-C values. So, if a patient has increased nonfasting TG concentrations, above 500 mg/dL (5.7 mmol/L), a repeat test should be done in the fasting state for at least 12 h and no alcohol for 24 h.
How does a clinician interpret nonfasting triglycerides?
Børge G. Nordestgaard: Nonfasting and fasting TG should be interpreted identically, as the mean difference between the two is clinically insignificant at only 26 mg/dL (0.3 mmol/L). Clinicians are interested in changes in TG of >100 mg/dL (1.1 mmol/L) and a single spurious high TG due to high fat intake will be followed by other measurements giving lower concentrations.
Anthony S. Wierzbicki: Nonfasting TG generally correlate well with fasting values. The presence of normal nonfasting concentrations excludes the presence of important increases in atherogenic TG–rich lipoproteins.
Samia Mora: As TG are the main lipid test that may be affected by food intake, a clinician needs to know the TG value that should be used for diagnosing and treating increased TG in the nonfasting state. TG increase after routine food intake by on average approximately 15% (and in some individuals by approximately 30%), unlike LDL-C, HDL-C, or TC, which often have clinically negligible changes (<5%). For clinical practice, it is important to have validated cutpoints for diagnosing and treating increased nonfasting TG. In a large prospective study from the Women's Health Study, we recently determined that a nonfasting TG concentration of 175 mg/dL (approximately 2 mmol/L) was the optimal clinical cutpoint for increased TG in the nonfasting state. This also corresponds to the nonfasting cutpoint recommended by the European Atherosclerosis Society and an Athens Expert Panel. Importantly, this is 25 mg/dL (0.3 mmol/L) lower than the cutpoint recommended by the AHA for high nonfasting TG (i.e., 200 mg/dL, 2.3 mmol/L) which would miss a substantial portion of individuals with abnormally high TG.
Neil J. Stone: The 2011 AHA Scientific Statement on Triglycerides and Cardiovascular Disease discussed nonfasting TG in detail: “In normotriglyceridemic subjects (i.e., fasting triglyceride concentrations <150 mg/dL; 1.7 mmol/L), consumption of a low fat breakfast (<15 g) before blood sampling would not be expected to raise postprandial TG values above 200 mg/dL (2.3 mmol/L). In these cases, no further testing for hypertriglyceridemia is indicated, although further discussion of lifestyle measures may be advocated on the basis of that individual's level of risk. However, if nonfasting TG concentrations equal or exceed 200 mg/dL (2.3 mmol/L), a fasting lipid panel is recommended within a reasonable 2–4 week time frame.”
Jacques Genest: With a grain of salt. While much time and research has been spent on postprandial TG as a cardiovascular risk factor, this response is often associated with the metabolic syndrome. Furthermore, the disappointing result of clinical trials using fibrates in addition to statins has led to a reevaluation of the benefits of treating plasma TG concentrations.
Greg Miller: TG will be increased to a variable and unpredictable extent when measured using nonfasting samples. Average influence from population studies may not translate to the influence on an individual patient's values. Clinicians will not be able to determine the extent of the influence of diet for an individual patient, so interpreting the results will lead to misclassification of risk. The same limitation applies to HDL-C and LDL-C.
Most recommended cutpoints for triglycerides are based on assays that correct for endogenous glycerol yet clinical laboratories use methods that do not. Do you expect a higher level of divergence in triglycerides values between the two approaches when nonfasting samples are used?
Børge G. Nordestgaard: Not accounting for the glycerol blank in outpatients and inpatients rarely affects the TG concentration by more than 9 and 26 mg/dL (0.1 and 0.3 mmol/L), respectively; such differences are clinically insignificant, and there is no evidence that this should differ between fasting and nonfasting samples.
Anthony S. Wierzbicki: Significant divergence with released endogenous glycerol is usually about 10%. More significant bias can occur in patients with highly increased TG values, those with type 2 diabetes, significant free fatty acid concentrations (e.g., stressed patients), or those on glycerol infusions.
Hubert Vesper: TG are determined by measuring glycerol after hydrolysis of TG. Thus, agreement among methods reporting TG is affected by their specificity to TG-bound glycerol, with some assays measuring total glycerol and others measuring only glycerol bound to fatty acids. About 5% of total glycerol is derived from free glycerol, except in certain diseases and conditions where glycerol values can be increased such as in Hirschsprung's disease or after heparin infusion. The impact of using nonfasting specimens on the among-assays agreement of TG methods and its impact on patient care is unknown. Further studies are needed to appropriately assess this issue as well as to better evaluate how total and fatty acid–bound glycerol affects a patient's ASCVD risk classification using both fasting and nonfasting specimens.
Samia Mora: This is a very interesting point. In the Women's Health Study that identified an optimal nonfasting TG cutpoint of 175 mg/dL (approximately 2 mmol/L), the endogenous glycerol was not measured. To my knowledge, clinical trials, epidemiological cohorts, and real-world community-based studies that measured lipids (including TG) using CDC-certified laboratories also would have used a correction for endogenous glycerol, similar to our study. Hence, all the guideline-recommended clinical cutpoints for TG are also based on glycerol-corrected TG. In the absence of diabetes and medications that are dissolved in glycerol, the contribution of endogenous glycerol to total TG is usually minimal [approximately 5 mg/dL (0.06 mmol/L)].
Greg Miller: For fasting samples, free glycerol is a potential confounder of TG in a small number of cases, typically those with genetic abnormalities in lipoprotein metabolism. These cases have sufficiently increased TG that it is unlikely the amount of free glycerol will influence assessment of risk for ASCVD. Glycerol is a common ingredient in processed foods and is also used as a dietary supplement. Nonfasting samples will have a variably increased amount of free glycerol that will be measured as TG by most clinical laboratory methods because they do not correct for free glycerol. Consequently, a postprandial TG measurement will be greater than a fasting value because of glycerol as well as fat in the diet. The influence of ingested glycerol will be variable since it depends on the food consumed and the time a sample is collected after a meal.
What are the laboratory's concerns regarding the use of a nonfasting sample? Are these concerns surmountable?
Børge G. Nordestgaard: 1) Fasting before a lipid profile measurement is believed to provide more standardized measurements; however, a high degree of precision is not needed clinically. 2) Fasting is believed to be needed to make calculation of LDL-C via the Friedewald equation; however, this equation also works fine with nonfasting measurements as long as TG are <400 mg/dL (4.5 mmol/L). 3) It is unclear what values should be flagged as abnormal; however, the same values can be flagged for all components of the lipid profile except perhaps to use TG ≥175 mg/dL (2 mmol/L) when using nonfasting and ≥150 mg/dL (1.7 mmol/L) when using fasting plasma lipid profiles.
Anthony S. Wierzbicki: Laboratories are concerned with nonfasting samples as most still calculate LDL-C. This is less of a problem if the laboratory has a reflex default to direct LDL-C measurement in the presence of increased TG. In addition, nonfasting samples may cause errors on laboratory systems by affecting enzymes or immunoassays if lipemia indices are set at low concentrations.
Hubert Vesper: Some studies suggest that the variability for LDL-C and TG is higher in nonfasting samples compared to fasting samples. The consistency among the different LDL-C assays in terms of the reported increase in LDL-C variability is not known and the reasons for such increases are not fully understood.
Measuring analytes that are less or only minimally affected by fasting status such as apolipoproteins or non–HDL-C in conjunction with the use of new risk assessment models could overcome current concerns related to nonfasting specimens.
Jacques Genest: The major concern lies in the precision and accuracy of the LDL-C determination. While some prefer to substitute non–HDL-C as the preferred measurement and therapeutic target, all clinical trials aim at lowering LDL-C. The greatest concern is that even a slight error in the measurement of LDL-C might lead to a reclassification of risk and a change in therapeutic approach (i.e., a change in dose of medication).
Greg Miller: A standard component of the lipid profile is to report the appearance of the serum after standing 8 or more hours at 4–8 °C. A creamy layer on the top is consistent with chylomicrons and a turbid serum appearance is consistent with an increased amount of VLDL. In nonfasting samples these appearance assessments will be confounded by the presence of these TG-rich lipoproteins from normal metabolism of fat in the diet. For example, it will not be possible to determine if the presence of chylomicrons represents a genetic abnormality in clearance of lipids from the diet or a nonfasting sample. An approach to manage this situation is to repeat lipid profile testing on a fasting sample when an abnormal appearance is noted.
LDL-C is most frequently calculated using the Friedewald equation, which should not be used when TG exceed 400 mg/dL (4.5 mmol/L) because the TG divided by 5 (when values are expressed in mg/dL) no longer appropriately estimates the VLDL-C. There are several reports that the Friedewald estimate of LDL-C is influenced by TG above 200 mg/dL (2.3 mmol/L) and the 400 mg/dL (4.5 mmol/L) nominal limit represents a point at which the error becomes excessive. Since nonfasting samples will have increased and variable amounts of VLDL, the Friedewald calculation will be less accurate even when TG are well below the nominal 400 mg/dL (4.5 mmol/L) limit. An increase of 50–100 mg/dL (0.6–1.1 mmol/L) TG from dietary influence will cause a 10–20 mg/dL (0.26–0.52 mmol/L) decrease in the apparent LDL-C value that is large enough to influence classification of risk for cardiovascular disease. Furthermore, the Friedewald equation is not suitable for use when chylomicrons are present because the equation has no correction factor for the cholesterol content of chylomicrons. Nonfasting samples are likely to contain chylomicrons depending on the fat content of a meal and the time since consumption, causing inappropriately decreased values for a Friedewald estimated LDL-C. The influence of nonfasting samples on the accuracy of HDL-C and LDL-C measurements will be difficult to assess for an individual patient. The measurement procedures will give numbers and the clinical care provider will not be able to determine if the laboratory test results were excessively influenced by the nonfasting condition. Considering the trend in guidelines to treat with statins at relatively low levels of risk, the net influence of compromised laboratory results may be difficult to discern because a large fraction of people are treated. In addition, observations from large population studies typically represent how the average of the group responds and may not suitably represent whether individuals might be misclassified regarding risk for ASCVD when laboratory testing is compromised by nonfasting samples. There are no mitigations for the influence of nonfasting on measurement of lipoproteins.
Survey data show that the analytical performance of total cholesterol and triglycerides is adequate but not for HDL-C and LDL-C. Do you anticipate the performance of the latter two to deteriorate further with the use of nonfasting samples?
Anthony S. Wierzbicki: Performance of most modern HDL-C assays is not affected until TG values exceed 885 mg/dL (10 mmol/L). LDL-C is affected by TG values, especially if calculated LDL-C is the primary laboratory result. Less bias occurs with direct LDL-C assays, but again significant background lipemia will affect the assay once TG concentrations exceed 885 mg/dL (10 mmol/L).
Hubert Vesper: The reasons for the variability among HDL-C and LDL-C assays are not yet fully understood. The specificity of different assays for various lipid particles might in part explain the currently observed among-assay variability. Nonfasting samples may have different particle compositions compared to fasting samples, which may cause a greater variability among HDL-C and LDL-C assays. Studies have shown that the analytical performance of HDL-C and LDL-C is adequate for some but not all patients, particularly those with chronic conditions. While the use of fasting specimens can minimize the among-assay variability, it will not eliminate discrepancies among these assays observed in certain patients.
Jacques Genest: A major question for the clinician is: “Does this matter?” We all accept that a measurement error of 3%–5% is an acceptable norm in a laboratory. Clinically, the tolerance for laboratory variability is greater, especially when looking at results over a long period of patient follow-up.
Greg Miller: Direct methods for both HDL-C and LDL-C are influenced by abnormal amounts of VLDL, chylomicrons, and other lipoprotein particles in a sample. These direct measurement methods use complex surfactant, polymer, and ionic reagents to selectively activate or inactivate the lipoproteins being measured. Changes in the ratios of lipoprotein particles influence the effectiveness of the reagents to isolate the component of interest for measurement. Nonfasting samples have altered ratios of lipoprotein particles from diet in addition to any pathophysiologic condition, and the ratios will be different depending on the meal and the time after the meal a sample is collected. Most direct HDL-C methods are generally satisfactory for measurements on fasting samples from people with normal lipid metabolism and thus normal ratios of lipoprotein particles. HDL-C results become more variable (both positive and negative biases) when abnormal amounts of lipoproteins such as VLDL and chylomicrons are present. Results from direct HDL-C methods will be more variable and less accurate for nonfasting samples due to variably increased amounts of VLDL and chylomicrons from the diet.
The currently available direct measurement procedures for LDL-C have marginal performance according to the National Cholesterol Education Program recommended bias and imprecision goals for people with normal lipid metabolism and are highly influenced by the presence of abnormal quantities of other lipoprotein components found in people at increased risk of ASCVD. Since nonfasting samples will have increased VLDL and chylomicrons from diet, the direct LDL-C methods will give less accurate results (both positive and negative biases) even for people with relatively normal lipid metabolism. Direct LDL-C methods are a poor choice for people with TG above 400 mg/dL (4.5 mmol/L) when the Friedewald equation is not suitable because of the fairly large biases caused by abnormal amounts and types of lipoproteins. Using nonfasting samples for lipid profile testing is likely to increase the number of samples that will need to have LDL-C measured by an alternate approach such as ultracentrifugation-based methods or lipoprotein particle counting.
Dr. Stone, why did the ACC/AHA guidelines prefer the use of fasting over nonfasting sample for routine lipid testing?
Neil J. Stone: The guidelines stated preferred not mandatory. For global ASCVD risk assessment, the pooled cohort equations that were introduced in the ACC/AHA risk assessment guideline don't require fasting samples as they use total cholesterol and HDL-C as lipid inputs. Thus, the determination of the risk score in the 2013 ACC/AHA cholesterol guidelines can be done with nonfasting lipids.
Three of the 4 statin benefit groups determined by the detailed literature review of the panel used LDL-C in their definition (fasting samples). For example, those with LDL-C ≥190 mg/dL (4.9 mmol/L), those 40–75 years of age with diabetes and LDL-C ≥70–189 mg/dL (1.8–4.9 mmol/L), and lastly lower risk primary prevention individuals with a 10-years ASCVD risk of ≥7.5% had to have an LDL-C ≥70 mg/dL (1.8 mmol/L). I would add that in the latter lower-risk primary prevention group, statin assignment wasn't automatic, but depended on a clinician–patient risk discussion. The guidelines further mentioned that an additional factor to consider if a risk decision is uncertain is an LDL-C ≥160 mg/dL (4.1 mmol/L). Also percent reduction in LDL-C is used to determine if the response to either a moderate- or high-intensity statin is adequate. The ACC/AHA guidelines point out that therapeutic response to statin therapy and safety should be regularly assessed and this should include a fasting lipid panel performed within 4–12 weeks after initiation or dosage adjustment and every 3–12 months thereafter. Thus, nonfasting lipids work well for ASCVD risk assessment but for other questions there is a role for fasting lipids. It depends on the question you are asking.
What are the financial implications of using nonfasting instead of fasting samples for lipid testing on the healthcare system, if any?
Anthony S. Wierzbicki: Nonfasting assessments are cheaper for the healthcare system as a whole as they reduce repeat patient visits at the cost of a small counterbalancing cost in the laboratory in dealing with a few samples with highly increased TG. Nonfasting samples are far more convenient for patients and enable health screening checks to be performed on an opportunistic basis rather than requiring additional scheduling and detailed explanation of a fasting protocol to the patient.
Børge G. Nordestgaard: It will likely lead to reduced costs, as the number of patient visits to laboratories and clinics will be reduced.
Samia Mora: I am not aware of any studies that have directly assessed the financial implications of using nonfasting samples for routine clinical testing or screening. Until those data are available, arguments in favor of measuring nonfasting lipids outweigh theoretical concerns and would be expected to reduce repeat visits, inconvenience to patients and providers, and overall healthcare costs.
Neil J. Stone: Since all of the global cardiovascular risk estimators use nonfasting total cholesterol and HDL-C, the ability to get point-of-care lipids for screening would avoid patients having to spend additional time obtaining a fasting test. Fasting lipids may be necessary as a follow-up, but the initial assessment of ASCVD risk can be made with nonfasting lipids.
Do you personally believe that nonfasting samples should be used for routine lipid profiles?
Børge G. Nordestgaard: Yes, we have already done that in Denmark since 2009.
Anthony S. Wierzbicki: Yes.
Hubert Vesper: Fasting samples should be used for lipid profiles that calculate LDL-C using the Friedewald equation and in risk assessment models that are based on fasting specimens. Fasting status controls for certain aspects that affect biological variability. Use of fasting specimens would eliminate retesting requirements in patients with suspected hypertriglyceridemia. Furthermore, fasting specimens may enable the use of different types of risk models, those requiring and those not requiring fasting specimens. Thus, lipid profile data obtained from fasting specimens may offer greater flexibility in terms of their use for a patient's ASCVD risk assessment.
However, nonfasting specimens may provide information about a person's ASCVD risk additional to that obtained with fasting specimens. Furthermore, apolipoproteins, lipid particles, and other new biomarkers may overcome some of the limitations of the current lipid profile. This could lead to new risk assessment models and probably new requirements regarding patient preparation.
Samia Mora: Yes, I have been using it for a while now. It's nice to see that recent guidelines or statements from the UK (e.g., NICE and the Joint British Societies on cardiovascular risk assessment) and the European Atherosclerosis Society are now recommending nonfasting lipids as the routine. Here, across the Atlantic, several major hospitals, laboratories, and even some cities have already adopted the approach of no longer requiring fasting when measuring routine lipid panels. In this era of increased awareness and focus on value-based therapies and diagnostic testing, the time has come for US guidelines to also embrace nonfasting lipid testing for routine clinical care.
Neil J. Stone: No. I don't think they should be used for the “routine” lipid profile. I would prefer that clinicians could choose between two panels based on their question:
Fasting TC, TG, HDL-C, LDL-C, non–HDL-C, or
Nonfasting (8 h or less) TC, HDL-C, non–HDL-C, and if requested TG.
I use nonfasting lipids almost daily in my clinic but for specific reasons. For example, consider 5 types of individuals one might see in a practice of preventive cardiology:
Those with genetic lipid disorders. A nonfasting TC and HDL-C is a good screening test, but as stated in the ACC/AHA guidelines, if the nonfasting non–HDL-C is ≥220 mg/dL (5.7 mmol/L), it is useful to follow with a fasting lipid panel (and sometimes some additional tests) to aid in a more precise diagnosis of either a genetic disorder or a secondary cause of hyperlipidemia.
Those with metabolic syndrome who are at risk for diabetes and ASCVD.
A fasting TG that is increased (≥150 mg/dL; 1.7 mmol/L) is a marker for increased attention to lifestyle considerations as well as to medications that could be increasing TG. The metabolic syndrome construct can greatly aid in counseling patients on lifestyle. Some are dismissive of this construct because it is not the same as insulin resistance and not as good a risk predictor as a global risk score for ASCVD or measures of glycemia for diabetes. Patients, however, seem to take notice that improved lifestyle affects all 5 of the metabolic syndrome parameters.
Those with or greatly at risk for hyperlipidemic pancreatitis. A patient with abdominal pain in the emergency room with a nonfasting TG >1000 mg/dL (11.3 mmol/L) is likely to have hyperlipidemic pancreatitis. Fasting TG are useful in patient with pancreatitis in following the resolution of the hypertriglyceridemia. The very high concentrations seen with hyperlipidemic pancreatitis usually fall about 50% per day while patients are nil per os.
Primary prevention patients. For risk assessment, a nonfasting TC and HDL-C are all that is needed. A nonfasting TG could be useful if patient consumed a low-fat meal (<15 g) as noted earlier.
Secondary prevention patients. A fasting lipid panel allows you to calculate LDL-C by the Friedewald equation. A fasting TG contributes to an assessment of on-treatment risk if it is above or below 150 mg/dL (1.7 mmol/L). If above 150 mg/dL (1.7 mmol/L), these patients may greatly benefit from more intensive lifestyle change as a first approach. This can greatly improve all of the patient's metabolic risk factors. One caveat is that LDL-C by the Friedewald equation is not accurate below 70 mg/dL (1.8 mmol/L). Thus, there are inaccuracies in determining how much lower you get when you intensify LDL-C–lowering drugs in secondary prevention patients. Some hold that this is exactly why apolipoprotein B may be a useful measurement for those on therapy with cholesterol-lowering medication.
Jacques Genest: Absolutely. I have been treating patients for the past 25 years in a specialized cardiology prevention/lipid clinic. As with many of my colleagues, I have seen extremes of lipoprotein disorders that require the careful analysis of fasting lipid and lipoprotein lipid measurements. But, for the great majority of my patients, we perform these tests in the context of ASCVD prevention, which does not require a fasting sample.
Greg Miller: I will continue to provide a fasting sample for my personal lipid testing because there are enough variables in assessing risk for ASCVD without introducing nonfasting influences on the accuracy of the laboratory measurements.
↵10 Nonstandard abbreviations:
- LDL cholesterol;
- National Institute of Clinical Excellence;
- American College of Cardiology/American Heart Association;
- atherosclerotic cardiovascular disease;
- total cholesterol.
Author Contributions: All authors confirmed they have contributed to the intellectual content of this paper and have met the following 3 requirements: (a) significant contributions to the conception and design, acquisition of data, or analysis and interpretation of data; (b) drafting or revising the article for intellectual content; and (c) final approval of the published article.
Authors' Disclosures or Potential Conflicts of Interest: Upon manuscript submission, all authors completed the author disclosure form. Disclosures and/or potential conflicts of interest:
Employment or Leadership: N. Rifai, Clinical Chemistry, AACC; I. Young, Queen's University Belfast, Belfast Health and Social Care Trust, Department of Health, Social Services and Public Safety, Government of Northern Ireland, IFCC, and Clinical Chemistry, AACC; A. Wierzbicki, National Institute of Health and Clinical Excellence UK; G. Miller, Clinical Chemistry, AACC.
Consultant or Advisory Role: S. Mora, Pfizer, Lilly, and Cerenis Therapeutics.
Stock Ownership: None declared.
Honoraria: None declared.
Research Funding: A. Wierzbicki, institutional funding, Site Clinical Trialist for Amgen (evolocumab) and Site Clinical Trialist for Merck (anacetrapib).
Expert Testimony: None declared.
Patents: None declared.
- Received for publication December 10, 2015.
- Accepted for publication December 29, 2015.
- © 2015 American Association for Clinical Chemistry