Manual of basic techniques for a health laboratory - libdoc.who.int

11. Immunological and serological techniques 347positive result from a screening test for syphilis may be due to other heterophileantibodies, faulty technique or to the presence of other treponemal antibodies. Anegative result may mean one of the following:● The infection is too recent to have produced detectable levels of antibodies.● The test is temporarily non-reactive because of treatment the patient isreceiving.● The test has been rendered temporarily non-reactive because the patient hasconsumed alcohol prior to testing.● The disease is latent or inactive.● The patient has not produced protective antibodies because of immunologicaltolerance.● The technique is faulty.Weakly positive results may be due to:— very early infection;— lessening of the activity of the disease after treatment;— nonspecific immunological reactions;— incorrect technique.The greatest value of the non-treponemal tests is in screening following therapyand in the detection of reinfection.TPHA testThe TPHA test is also used in the confirmation of syphilis. In the first step of thetest, diluted serum is mixed with absorbing diluent containing non-pathogenic Reitertreponemes. The serum is then transferred to a microtitre plate and erythrocytessensitized with killed T. pallidum organisms (Nichols strain) are added. If the testresult is positive the erythrocytes will form a smooth mat of agglutinated cells.11.10.1 RPR testMaterials and reagents 1●●●●●●●●Test platesDisposable Pasteur pipettesSerological pipetteTest-tubes, 75mm ¥ 12mmTest-tube rackRotatorRPR antigenNegative, weak-positive and strongly positive controls● Sodium chloride, 0.85% solution (reagent no. 53).The above reagents are usually supplied as part of a test kit.Method1. Bring the test and control sera and RPR antigen to room temperature.2. Dispense one drop of each of the test and control sera on to the test plates andspread carefully in the individual wells.1Note: The reagents for the RPR test should be stored at 2–6 °C in the refrigerator.