Pregnancy Test False Positives

A pregnancy test false positive is a real disappointment if you're trying to get pregnant. And, it's pretty scary if you're not ready for a baby. Why do false positives happen?

Pregnancy tests detect a hormone in the blood called Human Chorionic Gonadotropin (HCG). When a woman is pregnant, HCG is produced by the developing baby's placenta. Normally, a woman who's not pregnant won't make any HCG.

Tests for HCG can be done on either blood or urine. Blood tests can detect lower concentrations of HCG than urine tests, so a blood test might detect a pregnancy sooner. However, urine tests are very accurate and can be used only a few days after a missed period.

Home pregnancy tests are urine tests. Most test kits contain a plastic stick with a special chemical that reacts to HCG. Depending on the instructions, you'll need to either urinate directly onto the stick or collect your urine in a cup and then dip the stick in. A window on the stick will show one symbol to tell you you've done the test right, and one to show you if you're pregnant. Other tests have you mix a special powder into the urine or drip some urine onto a test disk.

Home pregnancy tests are pretty good. The manufacturers say that they're over 99% accurate if used correctly. That means following the directions in terms of timing, use of the kit, and how long to wait for the results.

But, even with a 99% accuracy rate, one person out of a hundred will get an incorrect result. False negatives happen when the test says you're not pregnant, but actually you are. This is especially likely if you test too early. Doing the test on the first day of your missed period reduces the accuracy to only 80 to 90%. It's a good idea to wait a week and then test again. You might have miscalculated when your period was due, or your HCG levels might not have been high enough for the test to detect.

Why would the test say that HCG is present if it's not really there? There are several possible reasons.

It may be that the test did not work properly or that you misunderstood the results. Some tests are easier to read than others. If you want to be really certain that your test is positive, try purchasing two different brands and using one of each. Here are some other reasons why you might get a pregnancy test false positive.

Soap or detergent can cause a false positive. If your test requires you to collect your urine in a cup, make sure that the cup is clean. Cups that come packaged in test kits should be fine. But, if for some reason you've needed to wash the cup, make sure there is no detergent left behind.

Blood in the urine, due to kidney disease or a bladder infection, can also cause a positive result.

Certain prescription drugs can cause a pregnancy test false positive. They include:

• Anticonvulsants
• Anti-Parkinson's medicines
• Some tranquilizers
• Some diuretics
• Promethazine

If the test is clearly positive but you don't seem to be having a normal pregnancy, it's possible that the HCG is coming from a tumor. It's not common, but women can develop tumors in the reproductive tract that make HCG. These include trophoblastic disease and germ cell tumors. Both have a good cure rate if they are discovered early.

Trophoblastic tumors form when something goes wrong with the fertilization of an egg by a sperm. Instead of growing into a baby, the egg grows abnormally and becomes a tumor. Symptoms include vaginal bleeding during an apparent pregnancy, abdominal growth that happens faster than in a normal pregnancy, and severe vomiting that's worse than normal "morning sickness." There are only about 3,000 cases of trophoblastic disease per year in the United States.

Germ cell tumors form from unfertilized eggs in a woman's ovaries. Germ cell tumors often have no symptoms until they are advanced. Abnormal swelling of the abdomen is one possible sign. These tumors are rare, but it's important to get checked if you're concerned.

No matter how carefully you do the test, it's always possible to get a pregnancy test false positive. If your home test says you're pregnant, your very next step should be to call your doctor for an appointment. He/she will verify the result and, if you're really pregnant, get you started on prenatal care.

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