How to Read a Clinical Test for hCG

Doctors use hCG to confirm and monitor pregancies

Human chorionic gonadotropin, or hCG, is a hormone produced during pregnancy. According to the American Congress of Obstetricians and Gynecologists, most pregnancy tests are based on the detection of hCG. Modern hCG test kits, purchased over-the-counter, are easy, inexpensive and discreet. Your doctor will confirm pregnancy through a second, more accurate hCG test done through a medical laboratory. Your obstetrician will use hCG tests to monitor your pregnancy.

Instructions

1. Determine the test source. Medical laboratories are able to measure hCG in blood and urine specimens. Each detect the presence of this hormone, but the medical laboratory will report the results in different ways. hCG blood tests detect pregnancy earlier -- from six to eight days after ovulation -- than do urine tests -- which are accurate about two weeks after ovulation.

2. Determine whether hCG blood test results are qualitative or quantitative. Laboratories and over-the-counter pregnancy tests report qualitative results simply as positive or negative. Only pregnant women have human chorionic gonadotropin present in their blood or urine, therefore qualitative results establish whether a woman is pregnant or not. Qualitative tests are sensitive to very small amounts of hCG. Pregnancy.org reports new, more accurate urine hCG tests which report pregnancy as early as six days after you conceive, or one day after a missed period.

3. Locate your hCG level on your laboratory results. Non-pregnant women have undetectable amounts of hCG in their systems. Blood hCG levels nearly double each day during early pregnancy. Medical experts call this "doubling time." Doubling time is much slower for a woman experiencing an ectopic pregnancy, or an egg that implants outside of her uterus. Women with failing pregnancies will also demonstrate a slower doubling time, or may even report falling hCG levels.

4. Monitor falling hCG levels for women with failing pregnancies, until hCG reaches zero. hCG levels that fall but remain detectable indicate the presence of remaining tissue which surgeons must remove. Your gynecologist will test your hCG, until the levels reach zero.

5. Monitor hCG levels for patients battling trophoblastic disease, a group of tumors growing in a woman's uterus. Effective treatment causes hCG to drop, while a rising hCG indicates treatment is failing. hCG is also effective in detecting a recurrence of this disease; increased levels of hCG indicate the tumors have returned.

6. Determine any possible reasons for false positive or false negative readings. For example, drinking large amounts of water will dilute your urine, possibly leading to false negative results. Blood tests administered too early in the pregnancy will likewise provide false negative results. Certain antibodies may lead to false positive results in some women.

References

• American Congress of Obstetricians and Gynecologists; 2007
• Pregnancy.org: How Do Pregnancy Tests Work?; 2011