Pregnancy: Part 2 – Beta-HCG Level, β-HCG, Human Chorionic Gonadotropin (HCG)

Sample

1. This test is done on the serum or urine of the patient.
2. Can save serum at 2 to 8 °C for  24 hours for total HCG.
3. For more time keep serum at -20 °C.
4. Freshly voided urine first-morning sample is preferred and centrifuge at 900 x g for 10 minutes.
   • Can store urine at 2 to 8 °C for 48 hours.
5. β- HCG serum is stable for 7 days at 2 to 8 °C. For longer periods freeze it at -20 °C.

Indications

1. To diagnose the pregnancy.
2. To monitor the high-risk pregnancy.
3. Diagnose ectopic pregnancy.
4. Screening of Down’ syndrome.
5. Used as a tumor marker.
6. HCG level also used to monitor the therapy and progress of the disease.
7. This can be used as a tumor marker for the placental tumors and germ cell tumors.

Precautions

1. Negative tests if done in the early stage of pregnancy. This is a false-negative result.
2. Avoid a sample of hematuria and proteinuria which gives the false-positive test.
3. Hemolysis in the urine gives the wrong result.
4. Maybe negative in the diluted urine, so a morning sample is preferred because it is concentrated urine.
5. Take the history of drug use like diuretics and promethazine, may give a false-negative result.
6. Drugs like anticonvulsants, tranquilizers, and hypnotics give a false-positive result.
7. Radioisotope administered in the last one week may affect the result.

Pathophysiology

1. The HCG is a glycoprotein with, molecular weight of 37.900 D, higher carbohydrate portion as compared to other hormones,  and it is made of two subunits:
   1. Alpha (α).
   2. Beta (β).
2. The HCG is produced by the placental syncytiotrophoblastic cells.
3. Chromosome 6 code for the α-subunit, and Chromosome 19 code for the β-subunit.
   1. The peak of the β-HCG is 6 to 8 weeks.
   2. While α-HCG keeps on increasing.
   3. HCG stimulates the corpus luteum which produces progesterone in the first week of pregnancy.
   4. Progesterone:
      1. Prevents menses.
      2. It supports pregnancy.

5. The α- subunit is the same for all the glycoprotein Like LH, FSH, and TSH while the beta unit is unique for HCG.
   1.  Molecular weight is around 14,900, where 10,200 for protein and 4700 for the carbohydrate part.
6. Therefore the β-subunit is specific for HCG.
   1. The molecular weight of β-subunit is 23,000, for protein is 16,000 and 700 for the carbohydrate.
   2. The ratio of α-subunit to β-subunit increases two-folds between the first and third trimesters.
   3. The HCG and its β-subunit of HCG can detect early pregnancy and it is present in the blood and urine. This is excreted by the kidneys.
   4. β-HCG sensitivity can detect pregnancy as early as 6 to 10 days after the implantation of the oocyte.
   5. By one month the amount is the same in the urine and serum.
7. HCG will appear in the pregnancy as early as 10 days after the conception and found in the serum and urine.
   1. HCG  plays an important role in maintaining the functions of the corpus luteum during the first week of pregnancy until the luteoplacental shift of progesterone production has occurred.
   2. HCG also promotes steroidogenesis in the fetoplacental unit and plays an important role in stimulating the fetal testicular secretion of testosterone.
   3. The human fetal testes have specific binding sites for HCG.
   4. The maximum level of fetal testosterone in the fetus occurs around the time pf peak level of HCG secretion during the pregnancy.
8. In the first few weeks of pregnancy, its level rises where the serum level is higher than the urine level.
9. This is a blood test to detect beta-HCG (human chorionic gonadotropin), a hormone normally produced during pregnancy and some of the cancers.
10. The intact molecule of HCG is more specific for pregnancy.

8. After delivery HCG level falls rapidly in the first 2 to 3 days and undetectable after 2 weeks.
9. The persistence level of HCG means trophoblastic disease. It needs the workup of the patient.

HCG was detected by the following methods, (Pregnancy tests):

1. Biological method where the urine was injected into a rabbit (1920). Now it is obsolete.
2. An immunological method like agglutination inhibition test (AIT).
   1. β-HCG is a better test and it can detect pregnancy after 18 days of the conception in the urine.
   2. After the monoclonal antibody, the detection of the pregnancy improved and now pregnancy can be detected 3 to 7 days after the conception.

3. Radioimmunoassay (RIA).
   1. This is reliable and sensitive to detect the β-HCG unit of HCG.
   2. The best sample is the blood for RIA, but urine can also be used.
   3. RIA can detect pregnancy before the first missed cycle.
   1. Radioreceptor assay (RRA).
      1. This test is done on the serum and is very sensitive and accurate.
      2. 90 to 95% positive after 6 to 8 days of the conception.
      3. This test is very useful if someone wants to terminate the pregnancy, also good in the infertile couple anxious for the confirmation of pregnancy.
      4. This can detect the minute amount of HCG secreted in the ectopic pregnancy.
      5. This test is helpful in the monitoring of spontaneous abortion.
4. Home test kits are based on the immunometric or immunochromatographic technique.
   1. The detection limit is 50 IU/L.
   2. Their clinical specificity is 77 to 100%.
   3. While their clinical sensitivity is 31 to 100%.
   4. The high number of false-negative results is difficult to understand the literature.
   5. False-positive 1% results in urine are due to:
      1. Protein.
      2. Drugs.
      3. Bacteria.
      4. RBCs.
      5. White blood cells.
   6. False-negative results occur because the test usually does not detect level at a concentration of less than 25 to 50 IU/L.
      1. Cold reagents, high temperatures, and extreme pH give a false result.
5. If serum HCG is positive (raised) and do not have a pregnancy, means the placenta not properly implanted in the uterus, then it may indicate:
   1. Ectopic pregnancy.
   2. Miscarriage.
   3. Testicular cancer.
   4. Trophoblastic Tumor.
   5. Hydatidiform mole.
   6. Ovarian cancer.
6. If the urine test is negative, but clinically indicate pregnancy, then repeat the test within 1 to 2 days.
   1. A urine test may be negative when the serum is positive for HCG.

Normal

Source 2

• Qualitative test = negative (positive in pregnancy)
• Men = < 5.0 mIU/mL
• Non Pregnant women = < 5.0 mIU/ mL
• another reference
  • normal = <2 ng/mL
• Urine = > 25 mIU/ ml suggests pregnancy.
• β- HCG normal value = <2 ng/mL

Source 4

• Men = <5.0 mIU/mL.
• Nonpregnant women = <5.0 mIU/mL.
• Pregnant women:

Level of HCG	mIU/mL / IU/L
At implantation	10 to 50
1 week of gestation	5 to 50
2 weeks of gestation	50 to 500
3 weeks of gestation	100 to 10,000
4 weeks of gestation	1080 to 30,000
6 to 8 weeks of gestation	3500 to 115,000
12 weeks of gestation	12,000 to 270,000
13 to 16 weeks of gestation	up to 200,000
17 to 40 weeks of gestation	Gradual fall to 4000

• • • mIU/mL to IU/L =  the conversion factor is 1
  •                  HCG level during pregnancy:

1. HCG level in pregnancy:
   1. HCG is detectable after 6 to 8 days of the delivery when the level is around 10 to 50 mIU/mL.
   2. The HCG doubles every two days until the concentration is 1200 mIU/mL around 10 weeks.
   3. Then double every three days between 1200 to 6000.
   4. Now double every 4 days above 6000 till the peak is near the end of the first trimester and is around 100,000.
      1. 10 to 20m weeks is the peak level of 150,000 to 200,000mIU/mL
      2. 2nd and 3rd trimester is 10,000 to 50,000 mIU/mL.
      3. By the second trimester, the peak level is 10,000 (800 ng/mL).
   5. 20 mIU/mL or less during the first week of pregnancy suggests ectopic pregnancy.
   6. Sudden fall from the plateau, indicate threatened abortion.

The increased HCG level is seen in:

1. Pregnancy.
2. Ectopic pregnancy.
3. A hydatidiform mole of the uterus.
4. Choriocarcinoma of the uterus.
5. Seminoma of the testes.
6. Germ cell tumor of ovary and testes ( choriocarcinoma, embryonal cell carcinoma, and teratoma ).
7. Nonendocrine tumors:
   1. Bronchogenic carcinoma.
   2. Hepatoma.
   3. Lymphoma.

The decreased HCG level is seen in:

1. Therapeutic abortion.
2. Incomplete abortion.
3. Dead fetus.

Please read Part 1, for more details.

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