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Reaction of micro-precipitation with cardiolipin antigen
Last reviewed: 23.04.2024
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The reaction of microprecipitation with cardiolipin antigen to syphilis is normally negative.
The micro-reaction of precipitation makes it possible to detect antibodies to the cardiolipin antigen of the pale spirochaete. The micro-reaction of precipitation in isolated application serves not as a diagnostic, but as a screening test, in connection with which, on the basis of its positivity, the diagnosis of syphilis is not established, and the patient is subjected to diagnostic tests (DSC, ELISA). With the help of microreaction of precipitation, people subject to periodic medical examinations for venereal diseases, patients with somatic diseases, etc. Are examined.
There are several variants of micro reactions: VDRL (Venereal Disease Research Laboratory), TRUST (Toluidine Red Unheated Serum Test), RST (Reagin Screen Test), RPR (repid plasma reagin), etc. The RPR test (MR plasma with cardiolipin antigen) in 78% of cases with primary, in 97% - with secondary syphilis. VDRL test (MR inactivated serum with cardiolipin antigen) is positive in primary syphilis in 59-87% of cases, in secondary - in 100%, in late latent - in 79-91%, in tertiary - in 37-94%. The microreaction of precipitation is usually negative in the first 7-10 days after the appearance of a solid chancre.
In the case of positive results of VDRL, RPR tests, a titer of reactive antibodies can be determined. A high titer (more than 1:16) usually indicates an active process, a low titer (less than 1: 8) - a false positive test result (in 90% of cases), and is also possible with late or late latent syphilis.
The study of antibody titer in dynamics is used to evaluate the effectiveness of treatment. Decreased titer indicates a positive response to ongoing treatment. Adequate treatment of primary or secondary syphilis should be accompanied by a 4-fold decrease in the titer of antibodies by the 4th month and 8-fold by the 8th month. Treatment of early latent syphilis usually leads to a negative or weakly positive reaction by the end of the year. The increase in titer 4 times indicates a relapse, reinfection or ineffectiveness of therapy and leads to the need for a second course of treatment. In secondary, late or latent syphilis, low titers may persist in 50% of patients for longer than 2 years, despite a decrease in titer. This does not indicate ineffective treatment or reinfection, as these patients remain serologically positive, even if the treatment is repeated. It should be borne in mind that changes in titres for late or latent syphilis are often unpredictable, assessing the effectiveness of treatment for them is difficult.
In order to differentiate congenital syphilis from passive carriage of maternal infection, newborns need to conduct a series of studies to determine the titer of antibodies: a rise in titer for 6 months after birth is indicative of congenital syphilis, while in passive carriage, antibodies disappear by the 3rd month.
When assessing the results of VDRL and RPR tests in infants with congenital syphilis, it is necessary to remember the phenomenon of prozone. The essence of this phenomenon is that for agglutination antigens and antibodies in these reactions it is necessary that the antigens and antibodies are in the blood in an appropriate amount. When the number of antibodies significantly exceeds the amount of antigens, agglutination does not occur. In some infants with congenital syphilis, the serum antibody content is so high that in the undiluted serum there is no agglutination of antibodies and non-treponemal antigens used to diagnose syphilis (VDRL and RPR tests are not reactive). Therefore, in children examined for the diagnosis of congenital syphilis, the phenomenon of prozone is possible. To avoid false-negative results in such cases, it is necessary to conduct studies with serum dilution and without it.
The micro-reaction of VDRL may be negative in early, late latent and late syphilis in approximately 25% of cases, as well as in 1% of patients with secondary syphilis. In such cases it is necessary to use the ELISA method.
A false positive microprecipitation reaction is possible for rheumatic diseases (eg, systemic lupus erythematosus, rheumatoid arthritis, scleroderma), infections (mononucleosis, malaria, mycoplasmal pneumonia, active tuberculosis, scarlet fever, brucellosis, leptospirosis, measles, mumps, venereal lymphogranuloma, chicken pox, trypanosomiasis , leprosy, chlamydia), pregnancy (rarely), in the senile age (about 10% of people over the age of 70 years may have a false-positive micro-reaction of precipitation), with chronic m lymphocyte thyroiditis, hemoblastosis, the administration of certain antihypertensive drugs, hereditary or individual characteristics.
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