A hospital pregnancy test works by detecting human chorionic gonadotropin (HCG) in either blood or urine. HCG is a hormone produced by a woman once an egg is fertilized and implants in her uterus. HCG aids in maintaining the lining of the uterus so that the placenta is nourished and the fetus can develop into a healthy baby.
A pregnancy test can either be quantitative or qualitative. A qualitative test only detects the presence of HCG in either urine or blood. Usually this test is performed with urine much like a home pregnancy test. A quantitative pregnancy test, also called a beta HCG, measures the amount of HCG in the blood. This test is more accurate because knowing the exact amount of HCG means less chance of a false positive or false negative.
A qualitative test will require urine obtained in a specimen cup. It is performed with a prepackaged testing device that requires either drops of urine into a collection well or a test strip that will be dipped into the urine sample. Results are usually available in three to five minutes.
A quantitative test will require a blood specimen obtained by venipuncture. The amount of blood and time needed for the test will vary based on the hospital's lab and whether or not other laboratory tests will be performed.
According to the American Pregnancy Association, HCG can be detected in blood 11 days after conception and in urine 12 to 14 days after conception. Having a pregnancy test performed is important because the sooner a woman knows she is pregnant, the sooner she can change any habits that may be detrimental to herself or her baby.
Qualitative results will be read as either positive or negative by the health care provider based on instructions included with the testing device. Quantitative results will be read as either positive or negative based on the HCG level. The American Pregnancy Association states that a level of 5 mIU/ml or less is negative and a level of 25 mIU/ml or more is positive.
The health care provider can also estimate the gestational age of a fetus based on the HCG level. If a woman is already aware of her pregnancy but is experiencing a complication, the result can be used to determine if the levels are appropriate for her gestation. A low HCG level can mean that the date of conception is later than expected, or it can indicate complications such as ectopic pregnancy or miscarriage. High HCG levels can mean that the conception date is earlier than expected, multiples or a molar pregnancy. High or low HCG levels could also be present in a normal pregnancy.
Whether a hospital pregnancy test is quantitative or qualitative, a negative result can mean the absence of an implanted embryo or that the test was performed too early for HCG to be detected. A positive result should be followed up with an obstetrician to ensure that the pregnancy will be as healthy as possible. An abnormal HCG level will most likely require further testing and close monitoring by an obstetrician to ensure that the fetus is not compromised.