Chapter VII STD and HIV Blood TestsAdditional Serology Tests:Introduction Serology is the study of immune bodies in human blood. These immune bodies are the product of the defense mechanisms against disease-causing organisms in the body. The principle involved with serology is the antibody-antigen response. The antigen actually comes first, in that the antigen is the substance which “provokes” the body to produce antibodies. As we all know, the antibody is the substance which fights the invading organism. Antibodies take many forms because there are many forms of antigens which can invade the body. Some antibodies are:
We will discuss in this section, only the most common tests in the study of serology. As we examine these tests and their results, you will see that many of the tests rely heavily on the fact that the body produces certain specific antibodies in response to specific invading organisms, viruses, proteins, and any other foreign substances which attack our bodies. Test: Syphilis Clinical Implications: There are several tests for syphilis. Most can be performed in the standard hospital laboratory with minimum of equipment. However, some tests will require special equipment. Most standard tests depend upon the syphilis antibody, Reagin, in order to test for positive results. When syphilis is present, the body produces Reagin. There are other disorders which can also produce Reagin. Therefore, when the person has a positive test for Reagin, further testing is needed to determine if the person has syphilis or some other disorder such as leprosy, tuberculosis, malaria, mononucleosis, collagen disease, and a few types of viruses. Most standard screening tests for syphilis seek Reagin. It would be very costly to test for the actual infectious organism in syphilis, called treponema pallidum. But keep in mind that there could be a false positive result with this Reagin test. Tests for syphilis:
Also called The Kline Test or the Kahn Test or VDRL (Veneral Disease Research Lab) These can be performed rapidly and with minimum amount of equipment. They are only screening tests, and any positive results must be retested by a more specific procedure. If positive (reactive): Needs further analysis
These tests are slightly more specific. They use an antigen in the testing procedure which gives more reliability. However, even these tests are not 100% accurate or specific for syphilis. Therefore, if positive, the results must be checked with a more accurate test.
This is the most specific test for syphilis. The serum of the person is mixed with a sample of live syphilis organisms. The mixture is then observed for a very specific type of reaction. This reaction will indicate the presence in the body of antibodies for syphilis. This test is often performed in conjunction with tests similar to those above, in order to determine quantitative results in the reaction. It is also called the T. Pallidum compliment-fixation test (TPCF).
This is another good test for syphilis. It requires extensive amounts of equipment and time for the test. It is not quite as sensitive as the above test, so it will not be useful for detecting cases of late syphilis. The principle of this test causes the antibodies to be labeled with fluorescent dye so as to detect syphilis. The Serological Tests: Serological examination is important for the diagnosis of other types of disorders as well as for syphilis. Bacterial infections, viral infections, and others can be diagnosed by the use of serological studies. Listed here are some of the most common conditions in which the diagnosis can be aided by serology studies.
Antigens can readily be prepared for serological study from cultures of bacterial organisms. The most frequently used test is the agglutination test. This test takes the patient’s serum with its antibodies and mixes it with a lab prepared solution of that killed disease organism. The mixture will then agglutinate, or clump together, because of the antigen-antibody reaction. The degree to which they clump will not only confirm the original diagnosis, but will tell to what degree of, or concentration of, the antibodies are present. This test is used for all types of dysentery, tularemia, and brucellosis.
The presence of viral infection can be determined by certain serology tests. It is similar to the bacterial tests above, but two different samples of blood are needed, and from two different points in the illness of the patient. When a rise in the titer of antibodies is noted, a virus can be determined as the cause of the infection. The tests used, as we mentioned, are the compliment-fixation, the hemagglutination, and others.
There are also several other disorders which can be diagnosed by serological examination. These following disorders use very specific types of tests. They are uncommon disorders and the MD will use the results of these tests along with other test results in order to make the diagnosis.
The cold hemagglutination test, and the antistreptococcus MG tests, are used to diagnose this condition. Neither test is conclusive, and other tests are necessary to confirm. Again, these tests require nothing of the patient except the random venous blood sample (serum).
The compliment-fixation tests are used as well as other tests. The MD will need to see a significant rise in titer of antibodies in order to confirm this diagnosis.
The heterophile agglutination test, uses RBC’s fro sheep which normally do not react with human antibodies, when they do, and there is high titer indicated, mononucleosis is diagnosed.
These fungal infections in the deep tissues (lungs, for example), can be diagnosed by the same compliment-fixation test.
The C-Reactive Protein Test (CRPA), is a serological test for certain inflammatory diseases. C-protein is released when there is tissue inflammation or necrosis. When this C-protein and a certain antiserum are mixed, a reaction occurs leading to a positive result. The result is then graded from Plus 2 (1+) to plus 4 (4+), depending on degree of reaction. Diseases such as these can give positive results:
The Latex Agglutination test, or the rheumatoid arthritis test, makes use of a form of polystyrene latex and human gamma globulin. When this mixture is mixed with the serum from a victim of rheumatoid arthritis, the entire mixture will agglutinate, clump, and positively diagnose the disease. Summary: This concludes the serological studies. Nursing responsibilities for these tests are few. Prepare the patient for the blood withdrawal. There may be fasting before some of the tests. You may need to explain the results of the test to the patient. An accurate and detailed history is important. If it is not on the chart, the nurse should be sure there has been a history completed. Information from the history may significantly affect the results of some tests. Also, report any such significant findings to the MD; such as ingestion of drugs which may affect the test results. Next Chapter VII STD and HIV Blood Tests Continued
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