Specificity and detection limit of ten pregnancy tests.

Pregnancy tests have sufficiently low detection limits (25-200 IU/L of human chorionic gonadotropin, hCG) and good specificity as judged by lack of cross-reaction with lutropin (LH) and follitropin (FSH). However, little information is available on the specificity of the tests for subunits and fragments of hCG. The dominating form of hCG immunoreactivity in pregnancy urine is actually a 10 kD fragment of the beta chain of hCG called the core fragment. We have evaluated ten commonly used pregnancy test with respect to specificity for various forms of hCG and detection limit. Our results show that the detection limits of the tests are close to that claimed by the manufacturers and that the main form of hCG immunoreactivity detected is intact hCG. Four of the tests also measure the free beta subunit of hCG and one method also the hCG beta core fragment, but the detection limits were 7-70 fold those for hCG.