Table 1. Confirmation rate of samples with positive results in the THC screen.
Reference laboratoryaHospital laboratoryb
InfantsNoninfantsInfantsNoninfants
No. of screened samples14614 713229419 513
Age, yearsc0.00 (0.00–1.86)36.30 (2.30–99.43)0.00 (0.00–0.99)34.90 (1.00–91.30)
Positive screen results
    No. of samples383024142788
    Positives, % (95% CI)26.0% (18.9%–33.1%)20.6% (19.9%–21.3%)0.6% (0.3%–0.9%)14.3% (13.8%–14.8%)
Positive screen results not confirming
    No. of samples18 of 3824 of 30246 of 8d12 of 239e
    False positives, % (95% CI)47.4% (31.5%–63.3%)0.8% (0.5%–1.1%)75.0% (45.0%–105%)5.0% (2.2%–7.8%)
    Difference in confirm ratesχ2(1) = 601; P < 0.0001P < 0.0001, Fisher exact test
  • a ARUP Laboratories, Salt Lake City, UT.

  • b University of Iowa Hospital Laboratory, Iowa City, IA.

  • c Data are presented as the median (range).

  • d Only 8 of 14 samples testing positively in the urine screen had confirmatory testing performed.

  • e Only 239 of 2788 samples testing positively in the urine screen were sent for confirmatory testing.