Why can a test be positive? Why is there a false positive result? How to deal with a false positive test result

In view of the fact that we often so want to see the cherished // stripes, and sometimes we will even "see" them - I have collected several articles. Might come in handy this information. (sorry if this has already been posted)

First, an article about the frequently mentioned "liar" frautest!

FRAUTEST test

C (c o ntrol) - control zone. The appearance of this strip during the study shows that everything is in order with the system itself, the test result is RELIABLE.
T(test ) is the test zone. This strip, reacting to hCG in the urine, appears in the test zone and informs about the presence of pregnancy.

We draw your attention to the fact that the strips on the dough must be even., approximately the same color (although early dates pregnancy test strip may be slightly lighter than the control) and placed across the entire width of the control zone.

Also follows doubt a positive test result if the strip is blurry, barely visible or located at the junction of the plastic protective substrate and the base of the test (at the test strips).

Also, it should not be considered positive result white stripe. white stripe- this is an unmanifested reagent, which became visible due to the large amount of the test liquid that got into the test. In other words, if the woman were pregnant, then this reagent would stain and as a result, the test would show two full-fledged strips.

FALSE POSITIVE (no pregnancy, but the test shows a positive result).

Possible reasons:

- taking fertility drugs containing hCG (pregnyl, profazi) at the time of the test or if the time after the end of treatment is less than 10 days;

- the presence of tumors (chorion epithelioma of the uterus or hydatidiform mole);

– incomplete removal embryonic tissue after a previous abortion.

FALSE NEGATIVE (there is a pregnancy, but the test shows negative result).

Possible reasons:

- the test was done earlier due date(especially this result can be observed in women with irregular menstrual cycle);

- kidney disease and of cardio-vascular system, which prevents the release of hCG in the urine at normal concentrations;

- high fluid intake or diuretics before testing.

The mechanism of "work" of the pregnancy test

In pregnancy tests, immunochromatography is used - a type of chromatographic analysis based on the interaction of a substance (usually of a protein nature) with antibodies to it. The same principle of antigen-antibody interaction works the immune system organism, hence the name.

The determined substance is chorionic gonadotropin human (hCG) is a glycopeptide hormone secreted by the placenta during pregnancy. Appearance and fast growth the concentration of hCG in the body (and in particular in the urine) of a woman makes it sufficient reliable sign pregnancy. Usually, on the 7-10th day after fertilization, the concentration of hCG reaches 25 mIU / ml (international units per ml) and doubles every 2-3 days, reaching a maximum between the 8th and 11th weeks of pregnancy, and then decreases almost to zero by the beginning of the 3rd trimester. 25 mIU / ml is the minimum concentration of hCG detected using immunochromatographic tests.

How many days after ovulation can you test?

In principle, a positive result can be obtained already on the 7th day of post-ovulation. Embryo implantation takes 6-12 days, usually about 10 days. So it makes sense to wait 10-12 days after ovulation, but even then there are often false negative results(i.e., there is a pregnancy, but the test is negative).

Tests from different manufacturers have different sensitivities, most of them are designed to be used from the 1st day of a missed period. In 90% ± 5% of cases, by this time the embryo has already implanted in the uterine wall and begins to produce hCG. However, in 10% of cases, implantation has not yet occurred. With a delay of 1 week, implantation occurs already in 97% ± 3% of cases. However, in practice, the reliability of the tests is limited by their sensitivity, so the real reliability is somewhat lower. Because the hCG level doubles every 2-3 days, hence the recommendation: if the result is negative, if menstruation does not begin, repeat the test in a few days.

What do false positive and false negative test results mean?

A false positive result is when the test shows two lines in the absence of pregnancy. This happens when a woman takes drugs containing hCG, as well as with trophoblastic tumors. After spontaneous miscarriage or early abortion or removal ectopic pregnancy HCG remains in the body for some time, and the test gives false positive results (i.e., the pregnancy is no longer there, but the test is still positive). As in the case of taking drugs containing hCG, two quantitative measurements must be taken to obtain reliable results. hCG definitions with an interval of 2-3 days. A decrease in the level of hCG indicates that the pregnancy is no longer there. Thus, false positive results are relatively rare, in contrast to false negatives. The latter are obtained when the gestational age is still too short and the hCG level is too low to be detected by the test (or the test itself is not sensitive enough).

Reliability homemade test depends on various reasons:

The quality of the test itself. Products from different companies can vary significantly.
Expiration date of the test, conditions and place of its storage. It is believed that in most cases the test can be trusted, provided that it is bought at a pharmacy.
The state of pregnancy. During a pregnancy that is on the verge of miscarriage, hCG will be produced much less than during normal developing pregnancy.
Conditions for setting the test: the study must be carried out using the morning portion of urine, in which the maximum content of the hormone is observed; the evaluation of the test must be carried out, adhering to the time interval specified in the instructions.
Additional circumstances. The amount of hCG in the urine is affected by the diet and the functional state of your kidneys.
If you drank a lot of liquid the night before, or ate watermelon, or are taking diuretics (diuretics), the concentration of hormones in the urine will be too low, and the test will not notice them.
If you have protein in your urine (even if you don't know anything about it) - the test may give wrong result.
If you were injected with hCG to induce ovulation (Profazi, Pregnyl) or to maintain the luteal phase, then traces of this hormone may remain in your body for 10 days after the last dose of the drug, and, accordingly, a pregnancy test may give false positive result.
Also, the level of hCG can be determined a few weeks after normal delivery, caesarean section, spontaneous or medical abortion and in other cases specified above.

As a result, you can get incorrect information, and in both directions: there is no pregnancy, but the test seems to be positive. Or: there is a pregnancy, but the test is still negative. Both of these can be a source of great suffering.

Some tests in the absence of pregnancy show its presence (false positive result). On the contrary, there are situations when there was a pregnancy, and the test showed its absence (a false negative result).

What are the reasons for the so-called false positive and false negative results?

Often the cause of a false result is the incorrect performance of the test or the use of a test with expired validity.

With the introduction of hCG to induce ovulation (drugs "Profazi", "Pregnil") or maintain the luteal phase of the cycle, traces of this hormone can remain in the body for 10-14 days after the last dose of the drug, and, accordingly, a pregnancy test can give false positive result.

Alcohol, fatigue, stress, lactation, medication (including birth control pills and Postinor) do not affect the test results.

The cause of false positive results may be a tumor that produces hCG - chorionepithelioma or cystic mole, dysfunctional ovarian diseases, when the production of various sex hormones is impaired.

After a spontaneous miscarriage or early abortion or removal of an ectopic hCG pregnancy remains in the body for some time, and the test gives false positive results.

Home pregnancy tests are fairly accurate. If you get a positive result, you can almost certainly assume that you are expecting a baby. To confirm the news, you should visit a gynecologist.

But in some rare cases, your test may show a false result. It could be a false positive that you are pregnant but not actually pregnant, or it could be a false negative that you are actually pregnant.

Dr. Preeti Daniel, director of the London Medical Clinic, gives his explanation for the incorrect results.

Expired pregnancy test

Pregnancy tests are about to expire, which can lead to a false negative. Heat or humidity can damage the test strip when testing for pregnancy, and this can also cause exact result. When buying a test, you should pay attention to the date of its release.

Medicines

HCG is a hormone released by the placenta after the embryo implants in the uterus. This hormone can be found in the urine or blood of a woman even before conception. If you have been undergoing fertility treatment such as IVF and you have been given certain medications, this may cause a false positive pregnancy test result to be read. Fertility treatments involve the use of hormones that can mimic or even contain hCG.

Miscarriage

If a woman has recently had a miscarriage, then hCG levels can remain high in your bloodstream for several days, which can lead to a false positive result.

Medications

Some medicines can change the level of hCG in the blood. These should include benzodiazepines taken to relieve anxiety (Diazepam, Alprazolam), diuretics (Furosemide), and even an antihistamine such as Promethazine.

chemical pregnancy

In this case, sperm and egg meet, and the fertilized egg, that is, the embryo, is unable to implant in the uterus, which can lead to an increase in hCG levels.

Ectopic pregnancy

An ectopic pregnancy can lead to a positive pregnancy test reading and it really means you're expecting a baby. Unfortunately, the fetus is attached incorrectly. It is most likely in one of your fallopian tubes (the tubes that carry the egg to the uterus). This condition requires immediate medical attention.

If a woman has tested positive at home but feels sharp pain in the abdomen or she begins to bleed, it is vital to visit a doctor as soon as possible.

You took the test too long

You have taken the test and are looking forward to the answer. You may have been distracted from nervous anticipation and held the test for too long. This may give a false positive result. The reason for this response will be the evaporation of urine if it remains on the test strip for too long. long time. She may leave a faint line that may look like a positive answer. Doctors advise against reading a pregnancy test after the recommended time period (10 minutes).

Medical reasons

There are certain medical conditions that can affect the result of a pregnancy test. If you are suffering from a urinary tract infection, kidney disease, or ovarian cyst, this may change your test result.

Urinary tract infections or kidney disease can lead to sample contamination (appearance of red or white blood cells in the urine) and this may give a false positive result.

Ovarian cysts, cancer, or an abnormality in the pituitary gland (in the brain) can cause an increase in hCG levels or provoke the production of hormones that mimic hCG, which again leads to a false positive result. These types of oncopathologies often affect the production of a small amount of the hormone. Home pregnancy tests can be quite sensitive to any changes in the body.

Dr. Praeti emphasizes that the technology for producing home pregnancy tests for last years improved noticeably. It should be noted that the definition of conception requires manipulation in the morning. It is the test of morning urine that guarantees one hundred percent accuracy of the result.

Most women with a delay in menstruation get a rapid pregnancy test. It's pretty fast and exact way learn about the presence or absence of pregnancy. But sometimes the result discourages a woman: the test shows pregnancy, but the gynecologist does not confirm its presence. Or the woman is sure that she could not get pregnant, but the analysis shows the opposite. So can a test be false positive? Consider what express tests are and what are the reasons for obtaining a false positive result.

How pregnancy tests work

Despite the fact that several types of pregnancy tests can be purchased at the pharmacy, they all work on almost the same principle. The active substance of these tests reacts to a hormone that is produced by the chorion (future placenta). This hormone is called human chorionic gonadotropin or hCG for short. As a result of the reaction, an inscription appears or the color of the strip changes. It depends on the type of test system.

HCG begins to be produced by the embryo within a day after it is fixed on the wall of the woman's uterus. It was during this period that the chorion of the embryo begins to form. After that, after a few days, the concentration of the hormone increases to the value that can be determined by the test. Taking into account the fact that 7-9 days after conception and 1-2 days for the production of hCG should pass before the embryo is fixed, count on reliable result You can only from the first day of the delay of menstruation.

Reasons for a false positive pregnancy test

There are many reasons why a test shows a pregnancy that doesn't actually exist. Here are the most common reasons for this condition.

First of all, this may be due to the fact that the purchased test is expired or defective. If you can still avoid buying an expired test by looking at its expiration date, then it is impossible to determine a defective test. In this case, you need to do a control analysis after 1-2 days using a test from another manufacturer.

The reason for a false positive pregnancy test is a violation of the instructions for its use. It is very important to carefully read the instructions before use and carefully follow its instructions. Do not shorten or lengthen the time of the analysis, as this may also affect its result.

A test can be false positive if it was done when a woman has a tumor process, including a malignant one. Most often it occurs with an ovarian or stomach cyst.

Experts indicate the possibility of obtaining such a result if there has recently been a miscarriage, abortion or removal of an ectopic pregnancy. This is due to the fact that the hCG accumulated during pregnancy cannot disappear abruptly and still remains in the woman's body for some time. Sometimes a miscarriage occurs very early, and the woman may not be aware of her condition. In this case, the test will indicate pregnancy.

False positive test on pregnancy may be the result of a violation of the normal hormonal background at a woman. sometimes happens hormonal disbalance in the body, which leads to increased production of hormones that resemble hCG in structure and structure. If their concentration becomes high, the test will show two stripes (color change).

For some diseases, the doctor prescribes to the patient medications, which may lead to false positive analysis. As a rule, such drugs include hormonal drugs.

During menopause, a woman's body produces a small amount of hCG. But sometimes there are “bursts” in the production of this hormone. If a high sensitivity test is performed at this time, the result may also be false positive.

What to do if you receive a false positive pregnancy test

Modern pregnancy tests have a fairly high sensitivity. For most of them, it fluctuates between 97-99%. But if, nevertheless, a woman believes that the result of the analysis may be false positive, a second test should be done. It is best to do this in 2-3 days and purchase a test from another company for this.

The woman is 100% sure that there is no pregnancy, and two are visible on the test bright stripes. Common situation? This is a false positive pregnancy test. This result can occur for many reasons, ranging from misuse test strips and ending with psychological and physical factors. What is happening at this moment in the body? Is it worth it to see a doctor immediately?

What's wrong with the test strip?

The test used for is a fairly simple device. It has several features that help to understand how it works:

It is not the pregnancy itself that is detected and not the presence of the embryo in the uterus. The test shows if there is pregnancy hormone, or hCG, in the urine. This is a hormone that is produced in a woman's body during the first few days after conception has taken place. However, hCG appears not only during pregnancy. Perhaps there is another source that provokes its formation.
The test is not super sensitive. Therefore, he does not respond to minimum quantities HCG. As a consequence, it is possible false negative test for pregnancy.
It is important to clearly follow the instructions for using the test. Otherwise, either an extra strip will appear, or, conversely, the desired strip will not exist. Sometimes manufacturers may use low-quality reagents that make the test completely untenable. Naturally, it shows incorrect data.

Human factor

There are several common mistakes that women planning a pregnancy can make:

Due to inattention or ignorance of the rules for using the test, a woman may not heed one or another recommendation. One of them is the cleanliness of the container for collecting test material.
The expectant mother may violate the storage conditions of the test. And not only she. For example, during its transportation, liquid may accidentally spill onto the packaging.
Sometimes it's all about suggestibility. A woman can reveal indirect signs of pregnancy in herself. In this case, she will see a ghostly second strip on the test, which is not really there.

So, the test in some cases gives evidence that does not correspond to the truth because of its characteristics and in connection with psychological factors.

What's happening?

False positive pregnancy test on hand, no pregnancy. This is what the doctor said, and confirmed by ultrasound. Errors in the analysis are excluded. What in this case provokes an increase in the level of hCG and, as a result, the manifestation of the second strip?

The state of the body, which is in no way connected with the presence of pregnancy, but contributes to the appearance of this hormone in the blood. These may be tumors, recent miscarriages, abortions or ectopic pregnancies, taking medicines containing hCG. As an option - polycystic ovaries, cysts, cancer Bladder. In early pregnancy, the chance of miscarriage is 15%. confuse early miscarriage with menstruation is easy, so sometimes the test with two strips is considered false. However, even after bleeding, the test will show a positive result because hCG is still present in the body.
Some women do not test with urine, but with other fluids that their body secretes. It could be blood breast milk, saliva.
Menopause. During menopause, a woman's body has a small amount of hCG. Because of this, there is a second strip on the test, and the pregnancy itself, as well as its signs, is absent.
Failure of the hormonal system.

What to do?

Getting a false positive test requires a visit to a doctor. He will conduct research and tell you how to proceed. For example, to assess the accuracy of the analysis, he may advise using a test from another manufacturer.

Then the woman will receive a referral for additional tests in the laboratory. There, specialists will determine the concentration of hCG in the urine. In this way, it will be possible to determine the error or find the reason for subsequent examinations.

Reverse situation

It also happens that there are signs of pregnancy, but the test shows its absence. This is called a false negative pregnancy test.

By the way, it is more common than false positive.

There are several reasons for this phenomenon:

How to act so as not to make a mistake

In order for the test to show an accurate result, you need to follow a few simple rules:

Urine must be collected in the morning, because it is at this time that the concentration of hCG in the urine reaches its maximum.
Collect material for analysis in a clean and dry container.
Do not touch the control part of the test with your hands.
It is important that the packaging is intact, and the expiration date is in order.
You should not do the test before the delay of menstruation occurs.
The result should be evaluated no earlier than 5 minutes later.

Any woman can have false positive and false negative results as a result of the test. In the first case, the second strip is visible, but pregnancy and its signs are not.

In the second, the opposite is true: the woman is expecting a baby, and the test gives a negative result. These phenomena can be caused by many factors. There is no need to panic ahead of time - in both situations, it is advisable to immediately consult a doctor.

A little girl asks: “Dad, are two stripes good?”. And my dad got sick...

Two stripes is the result. Someone expected him for many months or years, did everything possible and impossible for this, but they seriously frighten or shock someone. There are different life situations, but it is necessary to determine or refute the presence of pregnancy, almost 100% of girls and women first of all turn to home tests. And often even before they have a delay.

A home pregnancy test is definitely good. It is available to each of us, simple and easy to use and quite informative. Today there are tests of four generations, each of which is more advanced. But they are all built on the same principle: special reagent reacts to hCG in the urine of a woman (if this hormone is present there) and appears as a second strip. Actually, this means that you are pregnant. But is it always?

Can a test show a false result?

We have already written a lot about . And if you read forums on the Internet on this topic, then immediately make sure that, and even often. This is why it is not recommended to end the study with a single test, but always make controls with a retest after a few days.

A pregnancy test may well show a false result - both negative and positive. A false positive result is the appearance of two strips on the test in the absence of pregnancy.

As we have already said, the second strip appears if the woman's urine contains hCG hormone, which begins to produce chorion immediately after fertilization. Every day the level of hCG increases, and the closer to the delay (and according to all the rules, not earlier than the next day after the menstruation has not come) you will test, the greater the likelihood that the reagent will react.

However, in some cases, human chorionic gonadotropin is produced in small amounts in the body for other reasons not related to the development of pregnancy in it. And then the test carried out against the background of hCG production may show two stripes, but this will not mean at all that the girl is pregnant.

Reasons for a false positive pregnancy test

Among the reasons for false positive pregnancy test results may be trophoblastic tumors (which form due to the overgrowth of the same cells that are responsible for the production of hCG), a recent abortion, or miscarriage, termination of an ectopic pregnancy - when the hCG that has grown against the background of a previous pregnancy in the woman's body has not yet had time to decrease. In addition, there are many medical preparations containing hCG, and while taking them, a pregnancy test can also show a false positive result. This happens if a woman, for example, is being treated for infertility with hormone therapy, or just a few days ago (no more than ten) she finished taking hCG-containing drugs.

Often, girls observe the so-called ghost stripes on the dough sheet - blurry, indistinct, barely noticeable or second stripes that appear only at a certain angle or under certain lighting. In some cases, this may indicate that the level of hCG in the urine is still quite low, and the test should be repeated after 2-3 days for greater reliability. But most often, ghost strips appear if the test was stored in the wrong conditions, it has expired or is of poor quality. The second indistinct strip only indicates that this place contains a reagent that would manifest itself in the presence of pregnancy.

If you doubt the result of the pregnancy test, then you need to take a blood test for hCG and be examined by a gynecologist. In any case, this will not interfere and will either confirm the test result or refute it.

Of course, all of the above does not mean at all that home tests are not suitable for research and always lie. In 97% of cases, they show a reliable result.

However, you should not take 2 strips of a pregnancy test as a final verdict before a doctor's examination. In the same way as 1 strip, consider it as a 100% absence of pregnancy. By the way, false-negative results happen much more often than false-positive ones.

Especially for- Elena Kichak