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DRVVT Controls

A brief question from friend and colleague Kirk Guyer, BioMedica Diagnostics, Inc: When a coag lab runs controls for DRVVRT, do they analyze the controls only based on clotting time or do they also use the ratio as a pass/fail criteria?

We’ve had two answers so far. Frequent contributor Dave McGlasson checks the ratio for DRVVT controls, though not the normalized ratio. At another facility, only the primary and confirmatory clotting times are logged. Awaiting additional responses.
Answer number three, added 4-20-20: From Larry Brace, PhD, Coagulation Consultants Laboratory, Chicago: If you don’t do the ratio, in my opinion you are missing the point of the assay. How can you depend on the assay results if your control results are not dependable? I don’t ever allow results to be reported if control results don’t fall within expected limits.

Some added information from an April 20 exchange between Kirk and Larry:
From Kirk:Thanks for your feedback. So when a lab is running LA samples, will they QC both their screen and confirm reagents at the beginning of the day and at the same time? I know that some labs batch the patient samples for LA testing. Does your institution automatically run a confirm as a reflex test for an abnormal screen result or will you run a mixing study before you run the confirm? I see published testing algorithms for many labs but I wonder if they actually follow the algorithm with their actual testing practices. Most indicate a mixing study for an abnormal DRVVT Screen result and then the confirm. I really appreciate your insight.
From Larry: I approached the 4 questions above in blocks of 2 (see below). The answers represent my experience across a few labs, mostly larger labs.
1 & 2. Most labs run these tests in batches. In this case, Q.C. is completed just prior to testing patient sample. That way if Q.C. fails, corrective action can be taken before testing of patient samples.
3 & 4  I know some labs will run the screen tests and only run the confirm if the screen is abnormal. My approach has always been to run both on every sample for which DRVVT (or STA-Clot LA) has been ordered. We did this to decrease the time required to report test results. As computer capabilities have improved, more labs may be going to reflex testing. As to the mixing study, most pathologists I have worked with (and I concur) insisted on a mixing study as part of an LA workup, either prior to or concurrent with the other tests in the LA panel. I hope this is helpful,

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