A modified rapid monoclonal antibody-specific immobilization of platelet antigen assay for the detection of human platelet antigen (HPA) antibodies: a multicentre evaluation.

BACKGROUND: The monoclonal antibody-specific immobilization of platelet antigens (MAIPA) assay is the cornerstone technique for the detection and identification of human platelet antigen (HPA) antibodies. However, the original technique described by Kiefel and colleagues requires approximately 8 h adding to diagnostic delay. Moreover, proficiency exercises indicate that there are substantial variations in the MAIPA protocol, and that these may account for interlaboratory differences in sensitivity and specificity. STUDY DESIGN AND METHODS: A review of current MAIPA assay protocols from six laboratories together with performance in quality-assessment schemes identified several key variables potentially affecting the assay results. An optimized protocol was derived and assay time reduced to 5 h. The modified rapid MAIPA (MR-MAIPA) assay was evaluated using 61 samples with a range of HPA antibodies typically encountered in cases of fetomaternal alloimmune thrombocytopenia (n = 22), post-transfusion purpura (n = 8), platelet refractoriness (n = 7) and other platelet immune conditions (n = 24). The sensitivity of the assay was assessed using three international standards and the recombinant HPA-1a antibody CamTran007. The results obtained were compared with the original findings obtained with the local MAIPA assays. In addition, four different glycoprotein IIb/IIIa capture monoclonal antibodies were evaluated for their effect on assay sensitivity. RESULTS: Complete concordance was found between the original MAIPA results and those obtained with the new assay when testing a selected panel of clinical samples. The modified assay had nanogram level sensitivity for the detection of HPA-1a antibodies and titration of HPA-1a and HPA-5b antibody sensitivity standards yielded end-points equal to or greater than the mean recorded in international workshops. CONCLUSION: The MR-MAIPA assay offers improved turnaround for the detection of HPA antibodies without loss of sensitivity.

Effect of beta-propiolactone on blood group antibody detection.

A panel of 50 blood group antibodies covering a range of blood group antigens has been tested in the presence of 0.25% beta-propiolactone as a possible means of reducing infectivity of high-risk HTLV III/HBsAg samples. 11/50 (22%) antibodies could not be detected by the indirect antiglobulin test, and 6/40 (15%) were undetectable by the two-stage papain technique.

Effect of sodium phosphonoformate on blood group antibody detection.

A panel of 47 blood group antibodies covering a range of blood group antigens has been tested in the presence of 680 mumol concentration sodium phosphonoformate as a putative chemical additive to serum to reduce infectivity of 'high risk' HTLV-III/HBsAg samples. No inhibitory effect could be demonstrated using the indirect antiglobulin test or prepapainized cell test.

An investigation into the effect of reagent volume on the spin indirect antiglobulin test.

Three polyspecific antiglobulin reagents were tested in a spin antiglobulin technique with 51 antibodies of varying blood group specificities in which the volume of antiglobulin reagent used ranged from 1 volume (35 microliters) to 3 volumes (105 microliters). Statistical analysis of results showed that a significant decrease in avidity and agglutination scores occurred as the volume of antiglobulin reagent used was increased ('volume effect'). The volume effect was shown by 33/51 (65%) of antibodies with all three antiglobulin reagents and by 48/51 (94%) of antibodies with at least one antiglobulin reagent. Only 3/51 (6%) failed to show the volume effect with all three antiglobulin reagents.