An international study on activated partial thromboplastin time prolongation. Part 2: Interpretative commenting

Providing evidence-based interpretative comments (IC) is an integral task of clinical laboratory professionals. It may be of special relevance for coagulation testing, where pathological first-line tests could trigger more specialized tests. Our aim was to evaluate the quality of ICs provided to the physician in two samples with activated partial thromboplastin time (APTT) prolongation.

Two lyophilized plasma samples and their respective fictional clinical cases (case 1: heparin contamination and case 2: factor VIII deficiency) were sent to European laboratories for APTT and APTT mixing test measurement, and elaboration of ICs based on their results. The quality of ICs was evaluated in terms of analytical classification, laboratory interpretation, advice to physician, clarity, length and whether the clinical question was answered.

A total of 214 laboratories were included. Classification of the analytical result was stated in 57 % of comments. Laboratory interpretation was found in 91 % of comments for case 1 and 83.3 % for case 2, among which 9.3 % and 6.5 % were considered wrong, respectively. Advice for the requesting physician was provided in 65.8 % of comments for case 1 and 61.2 % for case 2, among which 36 % and 4.7 % were considered wrong, respectively. More than 70 % of comments for both cases were evaluated as clear and of an adequate length.

A significant number of laboratories provide clear interpretations and helpful advice for the management of altered coagulation results. Nevertheless, the finding of several confusing and misleading comments highlights the need for recommendations on elaboration of interpretative comments.