Pregnancy testing

	Urine pregnancy test	Serum pregnancy test
Minimum hCG level for a positive test	Qualitative test: 20 to 50 milli-int. units/mL, depending on test	Qualitative test: 5 to 10 milli-int. units/mL, depending on test Quantitative test: 1 to 2 milli-int. units/mL for an ultrasensitive test
Causes of a false-negative test	Performed too soon after conception; hCG concentration is below threshold for a positive test The hCG isoform measured is different from the hCG isoform in the sample (pertains mostly to urine tests) Hook effect due to extremely high hCG concentration (>500,000 milli-int. units/mL, these levels are most commonly seen in gestational trophoblastic neoplasia)
Causes of a false-positive test	Operator error in performing or interpreting the test, particularly with home pregnancy tests. Chemical pregnancy (ie, recent pregnancy loss very soon after implantation). Exogenous hCG administered as part of infertility treatment or for athletic performance. Exogenous hCG should be cleared by two weeks post-injection. HCG secretion from a tumor. Pituitary hCG secretion, typically in perimenopausal women. Interference with the assay by anti-animal antibodies, anti-hCG antibodies, or other substances (eg, high doses of biotin serum test positive but urine test is usually negative). Familial hCG syndrome (rare genetic condition)

hCG: human chorionic gonadotropin.

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