How to use Chlamydia antibody testing in subfertility patients

Screening for tubal factor subfertility by means of Chlamydia antibodytesting (CAT) was introduced into the initial work-up of subfertile couplesseveral years ago. The results reported, however, are heterogeneous, and nouniformity exists in cut-off levels of titres, or in definitions of tubalfactor subfertility. We performed a prospective cohort study to evaluatethe implications of varying the definitions of tubal pathology and ofmodifying the cut-off levels on the clinical impact of CAT in predictingtubal factor subfertility. In 227 consecutive patients who attended ourfertility clinic, the Chlamydia IgG antibody titre was determined andrelated to tuboperitoneal abnormalities at laparoscopy as a referencestandard. According to received operating characteristic (ROC) curveanalysis, a titre of 16 is the optimum cut-off level. Increasing thecut-off level improves specificity and positive likelihood ratio (LR+), atthe expense of sensitivity and negative LR (LR-). Changing the definitionof tubal factor subfertility from unspecified tuboperitoneal abnormalitiesinto extensive adhesions and/or bilateral distal tubal occlusion improvesLR+, LR- and kappa significantly. We conclude that CAT is more accurate inpredicting severe distal tubal pathology than unspecified tuboperitonealabnormalities. Although from a statistical point of view a titre of 16 isthe optimum cut-off level, from a clinical point of view 32 or 64 may bepreferable, depending on the aim of screening and the inception cohort.