Blood test for hCG: when to take, norm and decoding
The content of the article:
- HCG blood test - what is it?
- When and how to take, timing
-
Interpretation of analysis results
Hormone rates depending on the duration of pregnancy
- What does an increase in the level of a hormone in the blood mean?
- Can blood test results be erroneous?
A blood test for hCG (human chorionic gonadotropin) is prescribed for the early diagnosis of pregnancy, as well as for suspected oncological pathology. HCG is a gonadotropic hormone, which normally begins to be produced in pregnant women by chorionic cells from 6-8 days of fertilization. Its main function is to stimulate the formation of the placenta. In some cases, the hormone can be produced in the body of non-pregnant women and even men in the presence of malignant hormone-producing tumors.
There is no consensus among experts as to whether an increased level of hCG leads to cancer or, conversely, it is a consequence of it. In this regard, in many countries of Western Europe and in the United States, the over-the-counter sale of dietary and homeopathic remedies, which include chorionic gonadotropin, is prohibited.
The basis of the action of test strips on pregnancy is the determination of hCG in urine
HCG blood test - what is it?
Chorionic gonadotropin consists of α and b units, or fractions. The first of them is identical to thyroid-stimulating and luteinizing hormones, and the second is unique to hCG, which is why its identification is of decisive importance in laboratory research.
The Β-unit of hCG begins to appear in the plasma a week after fertilization. Its concentration grows rapidly and reaches a maximum by 7-11 weeks of pregnancy, after which it gradually decreases. 7 days after termination of pregnancy (childbirth, spontaneous miscarriage, artificial abortion), hCG analysis should no longer be detected. Also, this hormone should be absent in the urine.
The main functions of human chorionic gonadotropin:
- preserves the corpus luteum and stimulates the production of progesterone;
- prepares the immune system for the adoption of the fetus;
- in male embryos, it stimulates Leydig cells responsible for the synthesis of testosterone;
- stimulates the function of the adrenal and gonads in the fetus.
The corpus luteum normally exists for 12-14 days, after which it undergoes a reverse development. During pregnancy, it is thanks to the action of chorionic gonadotropin that it not only does not regress, but, on the contrary, increases in size and synthesizes progesterone in significant quantities. In addition, hCG enhances the synthesis of steroids by the adrenal cortex, causing its moderate physiological hyperplasia in pregnant women.
The hormone plays a huge role in the formation of the placenta, stimulation of its functions, metabolic processes, promotes the proliferation of chorionic villi.
Indications for a blood test for chorionic gonadotropin are:
- early diagnosis of pregnancy;
- exclusion of pathologies of fetal development;
- suspicion of an ectopic pregnancy;
- suspicion of malignant tumors (in women and men).
The effect of the test strips on pregnancy is based on the determination of hCG in urine, but they show a reliable result only a few days after the delay of the next menstruation. It is not always possible or willing to wait that long. In this case, it is advisable to conduct a pregnancy test (hCG in the blood).
There are two types of laboratory blood tests for chorionic gonadotropin:
- Total HCG. Shows the onset of pregnancy already 6-8 days after fertilization. Normally, the level of the hormone in the early stages doubles every 48 hours and reaches its maximum by 10-11 weeks of gestation. In the second trimester, pregnant women are sent for prenatal screening, during which an analysis is made for total hCG (triple, quadruple test).
- Free b-hCG. The indications for its determination are suspicions of testicular (testicular cancer) and trophoblastic (chorionicarcinoma, cystic drift) neoplasms. In addition, the determination of free b-hCG is performed during the screening of the first and second trimesters of pregnancy in order to assess the risk of having a child with Edwards or Down syndrome. It should be understood that a positive laboratory test result does not mean the presence of a chromosomal abnormality in the developing fetus, but only puts the woman at risk and serves as the basis for further more in-depth examination.
When and how to take, timing
To correctly determine the level of chorionic gonadotropin, it is necessary to donate blood in the morning on an empty stomach. It is advisable that at least eight, and preferably ten hours have passed after the last meal. One day before donating blood, you should limit physical activity.
If the patient is taking medications containing hCG, it is imperative to warn the doctor about this. Any other drugs do not affect the test result.
Often the question arises of how long a blood test will show that a pregnancy has occurred. As mentioned above, a positive result can be detected as early as a week after conception. But for greater accuracy, the study is best done on the 4-5th day of the delay in menstruation. If the level of hCG in a woman's blood is in the range of 5-25 mU / l, pregnancy cannot be reliably confirmed or denied. In this case, it is recommended to take the test again in 48–72 hours.
To determine hCG, blood is taken from a vein
In the II trimester of pregnancy, the level of chorionic gonadotropin is determined in order to identify possible fetal anomalies.
After a spontaneous miscarriage or medical abortion, a woman is recommended to donate blood for hCG for 3-4 days. Its increased level indicates incomplete removal of the ovum from the uterus.
The determination of the content of chorionic gonadotropin in the blood is carried out by the method of enzyme immunoassay, the blood for the study is taken from a vein. The duration of a classic study is different in different diagnostic centers and on average is 1-2 days. In almost every laboratory, you can order a rapid test, the results of which will be ready in 1-3 hours.
Interpretation of analysis results
Decoding a blood test for chorionic gonadotropin looks quite simple. Normally, in non-pregnant women, the level of this hormone in the blood is 0-5 mU / ml. In men, its level should not exceed 2.5 mU / ml. With a normally developing pregnancy, a woman has a very rapid increase in hCG up to 7-11 weeks. This is reflected in the data in the table.
Hormone rates depending on the duration of pregnancy
| Pregnancy period from conception, weeks | HCG level, honey / ml |
| 1-2 | 25-156 |
| 2-3 | 101-4,870 |
| 3-4 | 1 110-31 500 |
| 4-5 | 2 560–82 300 |
| 5-6 | 23,100-151,000 |
| 6-7 | 27,300-233,000 |
| 7-11 | 20,900-291,000 |
| 11-16 | 6 140-103 000 |
| 16-21 | 4 720-80 100 |
| 21–39 | 2 700–78 100 |
Since in different diagnostic centers the indicators of the norm of the hormone in the blood may differ, it is best to contact the specialists of the laboratory where it was carried out to decipher the obtained analysis, and carry out repeated studies there.
What does an increase in the level of a hormone in the blood mean?
An increase in the level of chorionic gonadotropin in the blood of non-pregnant women and men occurs with malignant tumors of the gonads, uterus, lungs, and organs of the gastrointestinal tract.
During pregnancy, an increased level of the hormone is noted in the following cases:
- multiple pregnancy;
- early toxicosis;
- diabetes;
- gestosis;
- chromosomal abnormalities of the fetus;
- prolonged pregnancy;
- incorrectly established pregnancy period;
- cystic drift and recurrence of cystic drift.
Detection of a low hormone level in a pregnant woman is the basis for an urgent referral to a gynecologist, as this may be a sign:
- non-developing (frozen) pregnancy;
- ectopic pregnancy;
- placental insufficiency;
- threats of termination of pregnancy;
- true prolongation of pregnancy;
- intrauterine fetal death in the II-III trimester of pregnancy.
Can blood test results be erroneous?
A blood test for chorionic gonadotropin is one of the most accurate methods for early diagnosis of pregnancy, its accuracy reaches 98%. However, there are mistakes. False positive results can be due to the following reasons:
- taking medications containing hCG (Horagon, Pregnil);
- hormonal disorders;
- previously undetected malignant tumors.
False negative results of a blood test for chorionic gonadotropin can be a consequence of late ovulation and / or implantation of the ovum, non-developing or ectopic pregnancy.
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Elena Minkina Doctor anesthesiologist-resuscitator About the author
Education: graduated from the Tashkent State Medical Institute, specializing in general medicine in 1991. Repeatedly passed refresher courses.
Work experience: anesthesiologist-resuscitator of the city maternity complex, resuscitator of the hemodialysis department.
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