Reaction of micro-precipitation with cardiolipin antigen

The microprecipitation reaction of with cardiolipin Ag for syphilis is normally negative.

MR allows to reveal AT to cardiolipin Ag pale spirochetes. MR in isolated use is not diagnostic, but 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, EIA).With the help of MR, people who are subject to periodic medical examinations for sexually transmitted 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 Ag) is positive in 78% of cases at primary, in 97% - with secondary syphilis. VDRL-test( MR inactivated serum with cardiolipin Ag) 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% [Henry JB, 1996].MR usually are 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 ATs 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 result of the study( in 90% of cases), and also possible with late or late latent syphilis.

Study of the titer of AT 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 AT 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 can 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.

To differentiate congenital syphilis from passive maternal infection, newborns need to conduct a series of studies to determine the titre of AT: a rise in titer for 6 months after birth is indicative of congenital syphilis, while with passive carriage, ATs 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 of Ar and AT in these reactions it is necessary that Ar and AT are in the blood in an appropriate amount. When the amount of AT significantly exceeds the amount of Ar, agglutination does not occur. In some infants with congenital syphilis, the serum AT content is so high that in the undiluted serum there is no agglutination of AT and non-reptilian Ag 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. In order 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.

False positive microprecipitation reaction is possible with rheumatic diseases( eg SLE, 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 old age( about 10% of people over the age of 70 can have false-positive MP), with chronic lymphocytic thyroiditis, hemoblastoses, the reception of certain antihypertensive drugs, hereditary or individual characteristics.