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Reagent sensitivity and clinical interpretation

Here’s an interesting question from Anita D’Antonio.

Several of our hospitals Hematologists/Oncologists have concerns with the sensitivity of the reagent we use for Prothrombin testing. The reagent is Diagnostica Stago STA-Neoplastine Cl Plus with a 1.32 ISI. They believe the reagent is too sensitive and is generating needless consults and follow-up testing on patients who do not have a bleeding disorder. I believe the more sensitive assay is best. How can I present this information to the medical staff?

Anita D’Antonio

Click “Full Story” below to read David McGlasson’s response.
Good question Anita.

Sensitive reagents with low ISI’s will yield higher PT’s.  At one institution that I am involved with when we switched to a more sensitive reagent/instrument combination some physicians were up in arms due to the longer times being generated.  When we investigated we found that they were paying no attention to the new reference ranges we were generating. This was after we had published several notices and gave briefings to each department. We also found that many of them were using ranges that they learned in medical school.  In fact when I questioned one neonatologist about his issues I discovered that he was using a laboratory guide from Johns Hopkins from 1989.  Another hospital found that every time a PT level was 16 seconds or above several surgeon’s would order fresh-frozen plasma pre-op.  The clinical pathologist then instituted a program that only allowed the reporting of the international normalized ratio (INR).  Once that happened the problems with the so-called prolonged PT values became a non-issue.  To date we now only report out the PT value in cases where the individual is not on any anticoagulation and is being screened for a possible factor deficiency or interfering inhibitor.  Hope this helps.

David L. McGlasson


David is a staff researcher at Lackland AFB and has published over 200 articles including abstracts, manuscripts, book chapters and patents. Read Bio

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