Health Information

Introduction

The presence of hCG can be determined by using immunological techniques. The immunological tests are based on double antigen antibody reaction. The most commonly performed immunological test is known as Gravindes test.

Principle

Principle is to determine the agglutination of red blood cells of sheep coated with hCG. Latex particles could also be used instead of red blood cells of sheep.

Requisites

Antiserum from rabbit: Urine from a pregnant woman is collected and hCG is injected into a rabbit. The rabbit develops antibodies against hCG. The antibodies are called hCG antibody or anti-hCG. The rabbit’s blood is obtained and serum is separated. This serum containing hCG antibody is called rabbit antiserum or hCG antiserum. It is readily available in the market.

Red blood cells from sheep: The red blood cells are obtained from sheep’s blood. These cells are coated with pure hCG obtained from urine of the pregnant women. Nowadays. Instead of sheep’s red blood cells, the rubberized synthetic particles called the latex particles are used.

Urine: Urine of the woman who needs to confirm pregnancy.

Procedure

One drop of hCG antiserum is taken on a glass slide. One drop of urine from the women who wants to confirm pregnancy is added to this and both are mixed well. If urine contains hCG, all the antibodies of antiserum are used up for agglutination of hCG molecules. The agglutination of hCG molecules by the antiserum is not visible. Now, one drop of latex particles is added to this and mixed.

Observation and results

If the urine contains hCG, it is agglutinated by the antibodies of the antiserum and all the antibodies are fully used up. No free antibody is available. Thus, the absence of agglutination of latex particles confirms pregnancy. If the urine without hCG is mixed with antiserum, the antibodies are freely available. When the latex particles are added, the antibodies cause agglutination of these latex particles. The agglutination of latex particles can be seen clearly even with eye. Thus, the presence of agglutination of latex particles indicates that the woman is not pregnant.

Advantage of immunological tests for pregnancy

Immunological tests are more accurate. The result is obtained quickly within few minutes. These tests can be carried out very easily. The procedure is not cumbersome, as in the case of biological tests. The immunological tests can be performed on 5th day of conception. By biological methods, the tests can be performed only after 2 or 3 weeks of conception. This is because; the concentration of hCG required for producing changes in the animals is excreted in urine only after 2 or 3 weeks of pregnancy. Recently available immunological tests are more sensitive and involve single step method. These tests can be performed even in the first few days of conception.