College of American Pathologists

  Patient Safety in
  Coagulation Laboratories


Posted April 21, 2009

When performing the prothrombin time test, using the incorrect International Sensitivity Index (ISI) number can lead to patient harm, as it causes the International Normalized Value (INR) number to be erroneous. The INR normalizes Coumadin monitoring for prothrombin time values across reagent and institutional variances. Reporting erroneous INR values may lead to use of excessive or insufficient oral anticoagulant medication, which may result in bleeding or thrombotic complications in patients.

Laboratories must understand that the ISI is a critical component of the INR calculation and must be appropriate for the particular reagent-instrument combination.

CAP provides this alert to remind laboratories to review their INR calculation so that it is correct and appropriate for the new ISI value with each lot of PT reagent.

What can you do?

  • Check ISI value from the instrument/reagent manufacturer’s product insert.
  • Make sure the correct number has been entered in the coagulation analyzer, as applicable.
  • Verify that the correct ISI value has been entered into the laboratory information system (HEM.23220).
  • Verify comparison studies were performed to verify the new reagent lot number and make sure the calculation is correct (HEM.23290).

Using the wrong International Sensitivity Index (ISI) value can lead to serious patient harm. If a laboratory determines that they have been using the incorrect ISI values, the CAP provides some guidance to assist laboratories as follows:

  1. Determine the length of time the incorrect value has been in use and how many patient results have been affected.
  2. Verify that appropriate comparison studies were performed to verify the new lot number of reagent—if no, perform them now.
  3. Compare the corrected International Normalized Value value to the incorrect value originally reported and determine what, if any, patient impact there is and whether or not corrected reports need to be issued.
  4. Update the ISI value on the instrument (and/or in the LIS) and verify that the calculation is correct (compute manually and compare against instrument and LIS generated values).
  5. Issue corrected reports (and notify physicians of the corrected values) as appropriate and notify all physicians of the error that occurred along with an explanation of how this error affected their patients.
  6. Perform a Root Cause Analysis to determine why this error occurred and determine how to prevent it in the future.
  7. Training/Re-educate staff on the steps that must be taken when reagent lot numbers change, and update on any process changes being implemented based on RCA findings.

Thank you for your commitment to patient safety. As laboratory professionals, we have a responsibility to ensure quality, education and safety because “Every number is a life.™”