From Soha Abuelela. I’m using the ACL Pro Elite for PT and PTT testing in my lab using Hemosil Recombiplastin 2G reagent but I frequently notice sample results showing normal PT time in seconds with normal concentration but the INR is above the reference interval! Could you please help me with possible causes and your recommended solution? Thanks a lot.
Hello, Soha Abuelela, and thank you for your question. I’m checking with some colleagues from IL-Werfen, hope to have responses sometime on Monday, April 10.
Thanks to Dr. Emmanuel Favaloro for the comment.
Mismatches between PT and INR ‘normal ranges’ are common. The PT has a certain normal reference range (e.g., 9.4 – 12.5s). The INR may have its own independent ‘normal range’; although noting it is used for monitoring vitamin K antagonists such as warfarin, so the therapeutic range is actually more important; but let’s say your INR normal reference range is 0.9-1.2 as an example. The two ranges are likely to be independent. When the PT gets converted to an INR (=patient PT/MNPT^ISI), this will generate different INRs depending on the reagents MNPT & ISI values. Sometimes, the PT, even if normal (say 12.4 in above example), could yield an INR above the upper limit of the INR ‘normal range’ for a particular set of MNPT and ISI values.