Comparative analysis of the accuracy of urinary hCG tests in vitro.

OBJECTIVE To identify whether cutoff for sensitivity advertised by three pregnancy tests in urine are compatible to those reported by the manufacturer and to describe their diagnostic performance. METHODS The urine of a male volunteer was used to dilute recombinant β-hCG at defined concentrations of 0, 6.25, 12.5, 25, 50, and 100 mIU/mL. The tubes containing each of the concentrations were coded and blindly assessed for positivity in three different lots of hCG tests: Strip Test Plus®, BioEasy®, and Visitect Pregnancy®. The sample size was calculated for an alpha error of 5%, with a power of 99%. RESULTS All three brands, in their three lots analyzed, had 100% of sensitivity for detecting β-hCG, with 100% negative predictive value, using only negative controls and samples with concentrations equal or higher than the test cutoff (n = 180/brand). The accuracy of the tests was 83% (BioEasy®), 84%(Visitect®) and 91% (Strip Test Plus®). Strip Test Plus® had the best positive likelihood ratio (52.5), while Visitect® had the best negative likelihood ratio (zero). CONCLUSION The three brands have adequate sensitivity for the advertised cutoffs. The Strip Test Plus® test had the best performance to identify urinary concentrations of β-hCG > 12.5 mIU/mL, and consequently, to confirm pregnancy, while Visitect® had the best performance to exclude β-hCG in urine (negative post-test probability: zero).