Situation:

A woman uses a pregnancy test. She interprets the results as being positive. Later, her period starts. She assumes she is the victim of a "false positive."

Commentary:

All traditional (non-digital) tests require proper usage and proper interpretation of the results to be accurate. Proper usage includes using the proper bodily fluid on the test! While nobody has has much fun experimenting with alternate fluids as I do (see Fun With HPT's for tests with breastmilk, blood, serum, and saliva) RESULTS OBTAINED WITH THESE FLUIDS ARE NOT RELIABLY ACCURATE. Breastmilk, for example, contains many hormones, and some may cross-react with a urine pregnancy test. Save yourself the trouble; if you want to trust your results, use only pee on pee tests!

Most often the error lies in the interpretation. It's easy to squint, tilt the test, scan it and invert the color with a photo program, or try any number of tricks to see a positive result. (I've done it-- I know that of which I speak!) All tests are prone to evaporation lines-- a gray, colorless, "ghostlike" line, or a "dent" in the test in the place where a positive line would be.

All tests have two antibody strips in the test window. One of these lines will always turn pink (the control line) when exposed to moisture. The other line will turn pink only if exposed to moisture with hCG (pregnancy hormone.) These antibody strips are not invisible. They are difficult to see, but they're there. When exposed to moisture, the "results" line becomes easier to see (because the moisture causes the light to reflect differently.) When you scrutinize the test, therefore, you will always see "something" there. Alas, it doesn't count unless it is obviously pink (or blue, obviously, if using a test with blue dye.) If you can't tell what color it is or it's too faint, assume it is negative.

Also, all tests have a strict time limit of 10 minutes. If ANY line of ANY color develops after 10 minutes (defined as "9 minutes, 60 seconds") you must assume it is negative.

Unfortunately many women convince themselves there is a real line when it is in fact an evaporation line. I did this myself and spent 3 days believing myself to be pregnant before my period started. Once I found out what an evaporation line was, I knew I had simply interpreted the results incorrectly and caused myself a lot of unnecessary heartache. Remember, the results of the pregnancy test don't determine whether or not you are pregnant . . . it's the other way around!

Solution:

The easiest solution to this problem is to use a digital test, which interprets the lines for you and displays the words "Pregnant" or "Not Pregnant" in a window for you. (Note: you CANNOT interpret the lines on the digital stick yourself. Most women will have 2 lines, even those who are not pregnant. See Secret of the Digital for more info.)

You don't need an expensive digital test for results, though. The best way to interpret your results accurately is to take the test and place it on a dry, flat surface. Set a timer for 9 minutes and 45 seconds (giving yourself 15 seconds to read the results.) View the test from the same distance you would read a book. If a PINK line is not visible at that point, throw the test away and leave it in the trash. (Bad things happen when you dig tests out of the trash . . . à lá my Cautionary Tale.)

Situation:

A woman pees on a pregnancy test. She sees a positive result. (She may take more than one test and receive more positive results. Sometimes she gets mixed results: some positive tests and some negative tests.) Later, her period starts. She assumes she had a "false positive."

Commentary:

Assuming she has interpreted her results properly and the test is truly reading positive, the most likely explanation for her period is a very early miscarriage, also known as a "chemical pregnancy."

Life in its earliest stages is very tenuous; there is a miscarriage rate of approximately 15% prior to the confirmation of a heartbeat. (Once a heartbeat is detected, the miscarriage rate drops to about 5%. After the first trimester is completed, the rate drops even farther.)

The most common cause of early miscarriage is a genetic defect. These are usually random and do not indicate that there are any big scary problems or will cause difficulty with future pregnancies. Other common causes are problems with a woman's blood clotting factor (cutting off blood supply to the embryo) or the presence of antibodies that attack embryos. If a woman experiences more than one early miscarriage she should consult her doctor and explore testing for some of these problems. (Good news: they can usually be treated with great success!)

When an embryo implants, it secretes a hormone known as hCG (human chorionic gonadotropin.) This is the hormone detected by pregnancy tests. "Early detection" pregnancy tests are often quite sensitive and can detect a pregnancy within a few days of implantation, often before a woman has even missed her period. When a woman is trying to conceive, she is much more likely to test early and therefore detect a pregnancy almost as soon as it happens! So, if a miscarriage occurs (which it does about 15% of the time) she is more likely to know about it.

When a miscarriage occurs, the amount of hCG decreases and eventually returns to a non-pregnant, undetectable level (non-pregnant women of childbearing age usually have 0-2.5 mIU/mL of hCG in their bloodstream and close to 0 in their urine. Post-menopausal women can have a level as high as 9.5, which may be registered as a positive on a very sensitive test.) Because hCG levels are so low in extremely early pregnancy, it decreases very quickly after a miscarriage. A woman who has a positive test one day may have a negative test the next day before miscarrying. This does not mean the positive test was "false."

NOTE: Having a positive test followed by a negative test does not mean that a woman will necessarily miscarry. I promise! Check out this FAQ for reassurance.

Solution:

Because true false positives are very rare, it is best to assume that a positive result is genuine. If you receive a positive result but begin to menstruate, you should assume you experienced an early miscarriage. If it happens again, you should consult your doctor. Many women have discovered (often-treatable) medical conditions (such as Factor V Leiden or antiphospholipid antibodies) as a result of repeat pregnancy loss.

However, since early miscarriage is so common, this may be a heartbreaking experience, but not something to worry about in terms of fertility or future childbearing.

Situation:

A woman pees on a pregnancy test. She sees a positive result. She has a blood test done at her doctor's office. The blood results are negative. Later, her period starts. Now she's mad at the test manufacturer for her "false positive."

Commentary:

A non-pregnant women usually has 0-2 mIU/mL† of hCG in her blood, with 0.5† being the average. (Peri- and post-menopausal woman can have up to 12 mIU/mL!)† There are two types of pregnancy blood tests: quantitative, which measures the quantity of hCG in the blood in numbers, and qualitative, which measures the quality of hCG (either positive-- reaching a predetermined cutoff point set by the lab, or negative.) A level of 5 or less is usually deemed "not pregnant" by labs. Some labs use a cutoff point of 20 or 25 as a "positive" threshold. In other words, they do something very similar to peeing on a stick-- except they use a test designed for blood instead of urine.

Most pregnancy tests are more sensitive than advertised (though not all tests, even among the same brand, are equally sensitive. If there are 3 tests in a box, they will all detect AT LEAST the advertised sensitivity-- say, 25 mIU/mL-- but one may detect 17, another 13, another 6.) Consumer Reports once found that First Response Earliest Result was capable, on occasion, of detecting as little as 4.5 mIU/mL. In other words, home pregnancy tests are capable of detecting very, very small amounts of hCG and detecting pregnancies very, very early.

The important thing to remember in this scenario is that when an embryo secretes hCG, it is metabolized into the blood first, and takes another day or two to reach the urine. Likewise, when hCG dissipates, it leaves the blood first. So, when a miscarriage occurs, the hormone will linger in the urine for a short while after it is gone from the blood.

So, it is entirely possible for a pregnancy test to detect a pregnancy and turn positive, followed by a negative blood test-- simply because the embryo has produced a small amount of hCG before dying. That small amount is enough to trigger a positive HPT, and small enough to dissipate from the blood stream by the time a blood test is conducted.

Solution:

Miscarriages are devastating. But it's devastating to be unsure if you've had one, too! While it can be incredibly frustrating to receive conflicting results, for the reasons outlined above, it is possible to be told "yes" by a pee-stick and "no" by a blood test. Technically both results are correct. At the time the pee-stick turned positive, hCG resulting from a pregnancy was present in the urine. And at the time of the blood test, that hCG had already dissipated due to miscarriage, resulting in a negative test.

Per the "solution" outlined in Scenario #2 above, I tend to think it is best to assume miscarriage rather than false positive in terms of identifying and treating any possible underlying medical condition in the event of repeat miscarriage.

Situation:

A woman pees on a pregnancy test. She sees a positive result. Later, her period starts. She blames a "false positive." She may or may not continue to see positive results even after her period has started.

Commentary:

When all is said and done, there are a few ways to have hCG in your urine without being pregnant! Post-menopausal women have some hCG in their urine. Usually it is such a small quantity that a pregnancy test can't detect it, but some super-sensitive tests might pick it up. Additionally, some forms of cancer (such as some kinds of bladder cancer) secrete enough hCG (or something molecularly very similar) to be detected by a test.

Lastly, some ovarian cysts secrete hCG. This should not be confused with Polycystic Ovary Syndrome (PCOS)-- these are different, rarer cysts. While PCOS may cause "false positive" results on ovulation tests, it does not cause false positive results on pregnancy tests.

Please note: while pregnancy can cause a positive ovulation test, the reverse is NOT true . . . ovulation CANNOT trigger a positive pregnancy test. (See OPK-as-HPT for an explanation.)

Of course, there are some medications that contain hCG and can cause positive pregnancy tests. Examples include A.P.L., Pregnyl, and Profasi. If you are taking hCG for any reason, ask your doctor how long to wait before you can take a pregnancy test. Oral contraceptives (the Pill), antibiotics, hormones, and other drugs CANNOT cause a false positive. ONLY drugs containing hCG can cause positive pregnancy tests.

Solution:

If you experience a positive pregnancy test that persists after your period has started, or you have any reason to suspect you are not actually pregnant in spite of a positive test, call your doctor.