A pregnancy test consists of measuring beta-hCG, a hormone produced by the placenta in pregnant women. A pregnancy test can be performed with blood for quantitative results expressed in milliunits of hCG per millilitre of blood or qualitatively in the urine with the result expressed as “negative” or “positive”. The technique used establishes a “positive” hCG concentration greater than 20 mIU/mL.
A negative result may indicate that there is no pregnancy in progress, that the test was done prematurely (preferably wait 10 days after a missed period) or that the urine specimen is too diluted (use the first urine in the morning). If in doubt, the test can be repeated a few days later.
A positive result indicates that a pregnancy is highly likely. Certain abnormalities and tumours of the placenta (hydatidiform mole) and ovaries also produce positive results. The presence of blood and protein in the urine specimen can sometimes lead to false positive results, while certain medications may lead to a false negative (diuretics, promethazine) or false positive (anticonvulsants, hypnotics, tranquilizers, etc.).