This case illustrates 2 very important points about laboratory testing for hemoglobin (Hb) disorders. The first is that most methods used for Hb identification are not sufficient as single, stand-alone methods. The only exceptions to this rule are DNA sequencing and mass spectrometry, but these methods are not used by many clinical laboratories because of the expense involved. It has long been a requirement in the College of American Pathologists checklist for hematology that Hb variants, particularly in the S and A2 positions, be confirmed by a second method. As illustrated by this case, performance of acid electrophoresis would clearly have shown that the variant in the Hb A2 position was not Hb C (Fig. 1⇓ ). Acid electrophoresis is easily able to distinguish between the 3 major variants that migrate in the A2 position: Hb C, Hb E, and Hb OArab. Other combinations of methods, however, can accomplish the same result.
Second, this case emphasizes that Hb analysis should not be interpreted in isolation but must be correlated with the patient’s clinical situation and other laboratory findings. The severe clinical course seen in this patient is highly unusual for Hb S/C disease. Furthermore, as was outlined, Hb S/C disease has very characteristic morphologic findings in peripheral blood smears. True sickle cells are rare in Hb S/C disease; their presence in this case was another reason to question the diagnosis. In cases such as this one, reconfirmation of a reported diagnosis is warranted, particularly if previous records are not available or if there are clinical inconsistencies.
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Authors’ Disclosures of Potential Conflicts of Interest: No authors declared any potential conflicts of interest.
Role of Sponsor: The funding organizations played no role in the design of study, choice of enrolled patients, review and interpretation of data, or preparation or approval of manuscript.
- © 2009 The American Association for Clinical Chemistry