The United Kingdom National External Quality Assessment Service for parasitology: toxoplasma serology scheme.

Aim: To examine performance in the UK National External Quality Assessment Scheme (UKNEQAS) for toxoplasma serology for evidence of discrepant results as compared with the predistribution and postdistribution results supplied by the toxoplasma reference laboratories.

Methods: Analysis of performance in the toxoplasma IgG and IgM schemes was made for the period 1994-2008 to look for trends in performance.

Results: For the IgG scheme, a mean of 98% of participants obtained the correct result for detection of toxoplasma-specific antibody. The most common problem was failure to detect low levels of antibody. In some cases this was the result of participants deviating from the manufacturer's instructions and using higher cut-off levels. For the IgM scheme, an average of 95% of participants obtained the correct result for toxoplasma antibody detection. The most common problem was the failure of some enzyme immunoassay kits to detect specific toxoplasma IgM antibody, which was detected by the more sensitive immunosorbent agglutination assay.

Conclusions: Performance standards in the UKNEQAS toxoplasma serology schemes were high. The problems encountered have highlighted the importance of detecting low levels of antibody, adhering to the kit manufacturer's instructions and selecting an appropriate assay for the clinical situation.