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Anti-IgA detection by particle gel immunoassay.

In this issue of Blood Transfusion, Oltean and colleagues1 assess results obtained with a rapid, semi-quantitative particle gel immunoassay (PaGIA) for the detection of anti-IgA in patients who have either had a transfusion reaction or are at risk of one in the event they receive any blood components or plasma fractions that contain IgA. Data obtained with the DiaMed ID-PaGIA Anti-IgA Antibody Test (Diamed GmbH, Cressier FR, Switzerland) were compared with those previously obtained using a more sensitive, quantitative fluorescence enzyme immunoassay (FEIA) for anti-IgA. The authors also used a PaGIA-based test to detect IgA in the same group of 40 partially or totally IgA-deficient patients (ID-PaGIA IgA Deficiency Test). Six healthy individuals were also investigated. Compared to the results obtained by the FEIA, the sensitivity and specificity of the PaGIA test for the detection of anti-IgA were 89% and 100%, respectively, and those for the detection of IgA were 92% and 97%, respectively. 
 
A limited number of other studies concerning the use of either or both PaGIA for the determination of IgA levels and antibodies to IgA have been published2–4. The study by Salama et al.2 assessed 105 normal healthy blood donors and 44 patients with either common variable immunodeficiency (CVID) and/or IgA deficiency (IgA <0.05 mg/dL) using the anti-IgA PaGIA method. Anti-IgA was not detected in any of the 105 healthy donors but was detected in 10 of 44 patients with IgA deficiencies (6 with IgA deficiency and 4 with CVID). Antibody-positive samples had titres from 2 to 256 as determined by serial dilution using the DiaMed anti-IgA PaGIA method. However, comparative results for anti-IgA using a reference method were not determined and IgA levels were also not assessed in parallel. 
 
Brown et al.3 tested 24 samples from patients for IgA and anti-IgA using the PaGIA IgA deficiency and anti-IgA tests and compared their results with those previously obtained for IgA by nephelometry (patients’ IgA levels ranged from 0.05 mg/dL). This study was limited by the use of a reference method of inadequate sensitivity for very low levels of IgA. With regards to anti-IgA results, only 2 of 18 patients were positive by the DiaMed test as compared to the haemagglutination assay data at antibody titres from 2 to 128. Although the DiaMed test results were compared to those of reference methods, unlike the study by Salama et al.2, and both IgA and anti-IgA tests were performed there were still relatively few IgA-deficient patients available for study. This is not, however, surprising in light of the relative rarity of patients with IgA levels at or below 0.05 mg/dL5. 
 
In the third study, Palmer et al.4 tested 198 donors and 36 patients for severe IgA deficiency and anti-IgA by PaGIA methods and compared their results to reference methods for IgA (enzyme immunoassay)6 and anti-IgA (passive haemagglutination)7. The enzyme immunoassay has a test range from 3.3–150 μg/L in 1:16 diluted serum (0.005–0.240 mg/dL in neat serum) with a limit of detection of 0.005 mg/dL6. By passive haemagglutination, anti-IgA2 titers as low as 10 had been reported7. For donors, the sensitivity and specificity of the ID-PaGIA for severe IgA deficiency were both 98% and for antibody they were 91% and 94%, respectively4. In patients, the sensitivity of the PaGIA was 94% for severe IgA deficiency and 67% for detection of anti-IgA. Both tests had a specificity of 100%. Antibody titers were not determined. 
 
In the present study by Oltean et al.1, samples from 40 patients were tested by both PaGIA methods and results then compared with those obtained by a more sensitive quantitative method (FEIA). By FEIA for anti-IgA, antibody titres 0.05 mg/dL). Nonetheless, comparison of the semi-quantitative PaGIA results with the more sensitive FEIA provides some insights into the PaGIA methods’ true limits of detection for anti-IgA or IgA. 
 
The main thrust of the report by Oltean et al.1 concerns the utility of the anti-IgA PaGIA assay as a rapid test for antibodies in patients at risk of transfusion reactions or for the diagnosis of anti-IgA-related anaphylaxis and guidance for the appropriate transfusion practice in an emergency situation. This report also assesses the utility of the PaGIA for detecting IgA deficiency which is also useful for identifying donors who could provide IgA-deficient blood products.