Summary
In 2010–2012, the North American Specialized Coagulation Laboratory Association (NASCOLA)
distributed 12 proficiency testing challenges to evaluate laboratory testing for protein
S (PS). Results were analysed to assess the performance of PS activity, PS free antigen,
and PS total antigen testing. Statistical analysis was performed on the numeric results
and qualitative classification submitted for each method. There were 2,106 total results:
716 results from PS activity assays, 833 results from PS free antigen assays, and
557 results from PS total antigen assays. The three assay types performed well in
the classification of five normal samples and nine abnormal samples, although certain
PS activity methods were more likely to classify normal samples as abnormal and one
PS total antigen assay was more likely to classify abnormal samples as normal. PS
activity methods were affected by interfering substances such as heterozygous or homozygous
factor V Leiden mutation (underestimation) and the anticoagulant drug rivaroxaban
(overestimation). In conclusion, NASCOLA laboratories using a variety of PS assays
performed well in the classification of clearly normal and abnormal samples. Laboratories
performing PS activity assays should be aware of potential interferences in samples
positive for FV Leiden or containing certain anticoagulant medications.
Keywords
Protein S - proficiency testing - NASCOLA - factor V Leiden - direct oral anticoagulants
