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).
Pregnancy tests; urine; reagent kits; in vitro diagnosis; chorionic gonadotropin
