27.10.2020

False positive pregnancy test

Chorionic gonadotropin begins to be produced even at the stage of early embryonic development of the embryo and is produced throughout pregnancy. The hormone ensures the normal development of pregnancy, prevents the rejection of the embryo due to effects on the immune processes. Therefore, the test gives a positive answer, since a substance that interacts with hCG is applied to the strip.

Early diagnosis of pregnancy using the test is based on the detection of the chorionic gonadotropin in the urine hormone. Human chorionic gonadotropin (hCG) is a protein hormone. It consists of two subunits (α and β) and a carbohydrate component. The hormone is secreted by trophoblastic cells of the human placenta.

The role of chorionic gonadotropin in the human body

In non-pregnant women, chorionic gonadotropin:

  • causes follicular maturation, ovulation and the formation of yellow bodies in the ovaries;
  • stimulates the synthesis of progesterone and estrogen;
  • improves the sensitivity of the uterus by acting on the inner layer of its cavity (endometrium);
  • stimulates the formation of new blood vessels of the endometrium.

In men, chorionic gonadotropin stimulates the secretion of testosterone by the gonads, initiates and supports the development of sperm.

Hormone production during pregnancy

In the urine and blood of pregnant women, there are various types of hormone – degraded, hyper- and hypoglycosylated molecules, free subunits, large subunits and their fragments. The primary indicator of pregnancy is the presence of free β-hCG.

Chorionic gonadotropin is used as a marker in pregnancy tests for independent use at home, and in clinical laboratories. Immunochemical testing for hCG in urine and blood is the main method for diagnosing a normal pregnancy.

Decreased hormone production is observed:

  • with a delay or cessation of fetal development;
  • with ectopic pregnancy;
  • with chromosomal Edwards syndrome in the fetus.

Increased secretion of chorionic gonadotropin is noted:

  • with multiple pregnancy;
  • with intrauterine infection;
  • with some malformations of the fetus (for example, Down’s disease).

Studies may also be conducted on various glycosylated forms of hCG. If on the day of introduction, glycosylated forms of the hormone in the urine comprise less than 50% of the total hCG, this increases the risk of miscarriage.

By the content of β-hCG in the blood, it is possible to judge not only about the course of pregnancy, its complications, but also about other health problems.

Chorionic gonadotropin production in pathological conditions

Chorionic gonadotropin is a reliable sign of trophoblastic diseases, as well as some malignant tumors. With these diseases, the hormone content in the blood and its excretion in the urine increases.

Trophoblastic disease

Trophoblast is the outer cell mass of the embryo. It forms a continuous cell cover of the entire embryonic complex, forms the epithelial cover of the villi of the fetal membrane, placental villi. Trophoblastic disease (synonyms: trophoblastic tumors, trophoblastic neoplasia) are always the result of genetic disorders of pregnancy.

The reason for the development of a trophoblastic tumor is a malignant transformation of trophoblast elements. This can happen during pregnancy (normal and ectopic), after childbirth or abortion.

Trophoblastic disease includes several forms of pathological conditions:

  • simple (full and partial) cystic drift;
  • invasive cystic drift;
  • choriocarcinoma;
  • trophoblastic tumor at the site of the placenta;
  • epithelioid trophoblastic tumor.

Bubble drift develops in the uterus (less often in the fallopian tube). It is detected in the period 11 – 25 weeks of the alleged pregnancy. There is no embryo, and placental cells grow in the form of bubbles with liquid, resembling a bunch of grapes. With incomplete cystic drift, the embryo arises, but it is not viable. Bubbles form in the placental tissue.
With invasive cystic drift, the tumor quickly and deeply penetrates the uterine muscle.

Choriocarcinoma is a malignant tumor that develops from the trophoblast epithelium. It deeply penetrates into adjacent tissues and vessel walls. In approximately 50% of cases, the disease develops from complete cystic drift, in 25% – from the villi of the embryo remaining in the uterine cavity after abortion, in 25% – after normal pregnancy.
A trophoblastic tumor at the site of the placenta occurs after childbirth. This is a dense tumor that grows in the lumen of the uterine cavity.

Epithelioid trophoblastic tumor is a rare disease. Grows in nodes, penetrates the uterine muscle membrane.

With timely diagnosis, trophoblastic tumors are completely cured in 95% of patients who did not have metastases, and in 83% of patients with metastases.

Malignant neoplasms

Chorionic gonadotropin can be produced by tumors of the testis, ovary, bladder, tumors of the gastrointestinal tract and lungs.
The release of hCG by osteosarcoma cells is described.

Can the test show a false pregnancy

Determining the content of chorionic gonadotropin using tests is a highly sensitive and accurate method for diagnosing pregnancy. But sometimes the results give a false positive or false negative answer.

A false positive pregnancy test gives a positive reaction (shows two bars) when there is no pregnancy.
A false negative test gives a negative answer (one strip) when pregnancy is.

False positive pregnancy test

The reasons for a false positive pregnancy test are as follows:

  • the use of the test against the background of taking medications that contain the hormone chorionic gonadotropin – Pregnil, Ovitrel, Horagon, Profazi; the hormone can remain in the body for 10-14 days after the last dose of the drug;
  • tumors that secrete the hCG hormone develop – trophoblastic disease, malignant neoplasms;
  • ovarian disease, when the production of sex hormones is impaired;
  • conducting a test within 4 to 5 days after an abortion or spontaneous miscarriage, since the hormone remains in the body for a certain time;
  • poor quality test.

The last cause of a pregnancy test error is rare.
A pregnancy test may give a false answer in the first two weeks after administering a medication to treat infertility. The test may show a false positive response within three weeks after birth and nine weeks after a miscarriage.

False negative result

The reasons for the false negative result:

  • short gestation, therefore, the concentration of hCG in the urine is insufficient;
  • kidney disease, which can lead to impaired urinary excretion of metabolic products;
  • other causes of renal filtration disorders – heart failure, arterial hypertension, atherosclerosis;
  • pregnancy pathology, in which the hormone level is reduced – the threat of miscarriage, non-developing pregnancy, ectopic pregnancy.

The cause of the false response is a highly diluted urine sample. Therefore, shortly before testing, you should not drink plenty of fluids. It is better to use the first morning urine sample.

To avoid a false answer when conducting a pregnancy test, it is important to follow the rules:

  • the test cannot be used after the expiration date;
  • it is necessary to store the test kit at a temperature of 2 – 28 ° C;
  • Do not touch the reaction zone of the test with your hands;
  • moisture or dirt should not get on the test;
  • you can not use the test in a fresh portion of urine, the study is carried out only immediately immediately after urination;
  • do not allow foreign substances to enter the urine sample.

Attention! Home tests are not a substitute for medical advice. If the test is negative and menstruation is delayed for 7 days, consult your doctor to rule out serious illness.

Causes of the phenomenon
  1. In men and non-pregnant women, an increase in hCG concentration is a likely sign of cancer growth.
  2. A positive test may be in non-pregnant menopausal women. This is due to an increase in the level of β-hCG during this period. Chorionic gonadotropin is produced in the pituitary gland. Its climacteric level is 6.4 + / 3.2 IU / L, and after the complete cessation of the production of sex hormones by the ovaries – 11.6 + / 7.0 IU / L and higher.
  3. False positive results of the analysis of chorionic gonadotropin can appear as a result of determining the hCG molecule, which is produced not by trophoblast, but in other tissues. These are hCG-like molecules lacking a carbohydrate component.

Sometimes the reason for the increase in the level of chorionic gonadotropin remains unclear. It is recommended that such patients be regularly examined for early detection of the growth of malignant tumors, since clinically it can appear after several months or even years.

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