Beta HCG Test for Pregnancy: Procedure, Normal range

Human chorionic gonadotropin which is also referred to as HCG is a compound secreted by the tissue developed during early embryonic development. This tissue after the embryo development progresses forms the part of the placenta. Therefore, measuring hCG levels is helpful in confirming pregnancy. The levels of HCG in blood and urine are detected to confirm the pregnancy. As compared to the urine test, blood tests for HCG are more accurate and specific.

Nowadays the preliminary investigation for the pregnancy is by using the home testing kits available over the counter at the pharmacists store. Although the kits are accurate in detecting the pregnancy, the physicians confirm the pregnancy by blood and urine tests. The blood and urine tests for confirming the pregnancy measure the human chorionic gonadotropin (HCG) levels. The sensitivity of the test is a reliable marker for confirming the pregnancy. Even blood tests are recommended over ultrasound detection for early confirmation of pregnancy. 

Procedure for Testing 

Nowadays, the tests for Beta HCG involve the detection of the binding of monoclonal antibodies to  HCG. In the HCG molecule the beta-subunits of interest. This test is a clear marker as the binding is specific and rules out the cross-reaction mostly with the luteinizing hormone which is commonly referred to as LH.

Following are the two types of investigations for HCG determination,

Urine Testing

• It is advised by the laboratory technician that urine samples should not be submitted by the patient drinking large amounts of water. It is observed that a dilute urine sample has greater chance to depict a  falsely negative test.
• The other interfering factor is blood traces in the urine sample. This may result in a false positive result for the urine test.

Serum Testing

• In order to conduct the serum testing, the laboratory technician obtains the peripheral blood for determining the serum HCG levels.

Normal Levels of HCG in Serum of Pregnant Women

It is postulated by the researchers that the HCG which is secreted by the tissue surrounding the developing embryo or more specifically referred to as implanting blastocyst is significantly detected in the maternal blood after about 6-8 days approximately post fertilization. The HCG levels thereafter seem to increase more rapidly and reach around peak values at nearly 7-10 weeks. 

The Beta hCG values for detecting pregnancy are given below,

1. The pregnancy test is negative: HCG value less than 5 IU/L
2. The pregnancy test is Indeterminate: HCG value is 5 to 25 IU/L
3. The pregnancy test is positive: HCG value is greater than 25 IU/L

The second range of indeterminate value is not conclusive and is suggested to undergo repeated HCG tests after a few days or suggested ultrasound. Also, the levels of the beta hCG are tested to monitor healthy pregnancy. Pregnancy with twin fetuses can be depicted with high values of beta hCG levels.

The over-the-counter available pregnancy test kits have a sensitivity of nearly 25 units per liter of urine. These OTC kits are known to show positive results within  3-4 days post-implantation of the blastula. It is noted that by nearly 7 days and nearly around the date of the start of menstruation, almost  98% of the positive samples will be detected as true positives. So, it is observed that any negative result even after one week of missing the period signifies that the woman is not carrying or pregnant. Also, the OTC test kits that are available depicting false positive test results because of any interfering substances is of rare occurrence. 

Conclusion

Beta HCG is a marker test for confirmation of pregnancy in blood and urine. Although it is an accurate test to confirm pregnancy, interfering factors can result in false positive and false negative results. In case of results that are non-determinant, it is advised to repeat the tests after a few days. Urine test is not reliable as compared to a blood test as dilute urine samples can have low levels of HCG for accurate detection. There are certain conditions that cause increased beta-HCG levels in the case of twin, ectopic, heterotopic pregnancy, and miscarriage. Also, the high levels of beta HCG depict abnormal germ cells, cells of the placenta, and the tissues of embryos.