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

336 Manual of basic techniques for a health laboratory11.3 Determination of rheumatoid factors by thelatex-agglutination technique11.3.1 Materials and reagents●●●●●Test plates (preferably with a dark background)Stirring rods, wooden orange sticks or rotatorTest-tubes, 5mlTest-tube rackMicropipettes● Latex rheumatoid factor (RF) reagent (aqueous suspension of latex particlescoated with human IgG)● Negative and positive control sera● Sodium chloride, 0.85% solution (reagent no. 53).The above-mentioned materials and reagents are usually supplied as part of a commercialtest kit.11.3.2 Method1. Bring the test and control sera and latex RF reagent to room temperature.2. Dilute the test and control sera 1:5 with sodium chloride solution.3. Apply one drop of each dilution to the test plates.4. Shake the vial of latex RF reagent and add one drop to each of the samples onthe test plates.5. Mix well with stirring rods or orange sticks (one for each sample) and rotate theplates gently (about 10 times), or place on a rotator.6. After 2 minutes, examine the plates and compare the reactions of the test serawith those of the control sera (Fig. 11.12).7. If any sera are positive, repeat steps 3–6, using a twofold dilution.The highest dilution of serum that causes agglutination is the titre.Fig. 11.12 Latex agglutination testa: Positive result; b: negative result.11.4 Tests for the determination of anti-streptolysin Oantibodies11.4.1 Anti-streptolysin O test (ASOT)Streptolysin O is a toxin produced by haemolytic streptococci. The anti-streptolysinO test (ASOT) is the most commonly used laboratory test for following a streptococcalinfection and its sequelae (rheumatic fever and acute post-streptococcalglomerulonephritis). Other approaches are now available, but the “standard” ASOTis based on the fact that streptolysin O will lyse human or sheep erythrocytes unlessneutralized by anti-streptolysin O antibodies present in the patient’s serum.