An evaluation of three commercial kits for use as screening methods for the detection of leptospiral antibodies in the UK

Aims-To compare three commercial screening tests-the PanBio leptospiral IgM enzyme linked immunosorbent assay (ELISA), the Biolisa leptospiral IgM ELI SA, and the indirect haemagglutination assay (IHA)-with the microscopic agg lutination test (MAT) and two "in house" ELISAs-urease and horseradish pero xidase (HRP)-for the detection of leptospiral antibodies in a local UK and fire population. Method-Two hundred sera submitted for a differential diagnosis of leptospir osis were tested by all methods. A further 142 sera from patients with anti bodies to toxoplasma, Epstein-Barr virus (EBV), hepatitis A virus, rheumato id factor, Borrelia burgdorferi, Mycoplasma pneumoniae, syphilis, cytomegal ovirus, and Q fever were tested for crossreactivity. Results-Compared with the MAT, sensitivity and specificity were found to be : PanBio, 90%/94%; Biolisa with sorbent, 100%/85%; and IHA, 54%/95%. Seven of 200 trial sera gave false negative results with PanBio; 14 of 200 trial sera gave false positive results with Biolisa with sorbent, as did a furthe r 25 of the 142 sera tested for potential crossreactivity. Two of 142 sera gave crossreactions with PanBio and IHA tone each). Conclusions-The degree of false positivity seen with the Biolisa suggests t hat the recommended positive value of greater than or equal to 26 Eu/ml sho uld be reassessed using pools of sera from local populations. When the cut off value was reassessed, using a value of greater than or equal to 40 Eu/m l, a sensitivity and specificity of 96% and 94%, respectively, was achieved . Even the modified Biolisa appears to be over sensitive and to show a high degree of non-specificity. The IHA, although specific (95%), lacked sensit ivity in this study. The PanBio appeared to be the most suitable as a scree ning test for leptospiral IgM in the UK, although it would be advisable for all positive test results to be confirmed by a different enzyme immunoassa y and the MAT.