Prothrombin time in an adolescent: right or wrong?

A 17-year-old young man had a determination of prothrombin time(PT) for a minor surgical intervention. The final value in percentage for the PT was 65% for a value of 15 seconds. Liver function tests and hepatic sonogram were normal. No drugs or coagulation deficits were detected.

Could you say what is the reason of this situation?

Prothrombin time is  measured in seconds and expressed as a percentage compared to the normal range established and maintained by the laboratory that performs the test. This normal range represents an average value of healthy people who live in that area. Adolescents and young adults have usually a physiological prolonged value expressed in seconds. The comparison of  this value with a reference control from an adult can give a false low value for the prothrombin time. The PT can change due to variations between different tissue factor used in the reagent to perform the test.

The Prothrombin time performed on a normal individual will vary according to the type of analytical system employed. The International Normalized Ratio (INR) is a measure used to standardize the results.

ANALYSIS:This is a Diagnostic error system-related because there were not a proper calibration for the test.