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PTT Controls Drift Upwards

From Mary Ann Tara:

Is there a way to validate partial thromboplastin time (PTT, APTT) results over the shelf life of a particular lot number? We recently experienced a serious problem with deterioration over time of our Actin FSL reagent. It initially was seen in a drift up and out of range for our abnormal control, but we were told by the manufacturer to just adjust that, as it was a problem just affecting that control and reagent lot.

However, we started seeing patients having slightly elevated APTT’s with no factor deficiencies, anticoagulation or lupus anticoagulant interference. When we tried a new lot of APTT reagent, there were huge differences in all our APTT’s, especially as the times got longer, affecting all patients,but especially our patients being anticoagulated.

It was verified that ” the performance of this lot has shifted over shelf-life.” What independent resource do we have to make sure that our APTT results are valid over time for a particular lot number? Thanks!

Mary Ann Tara, BS MT(ASCP)
Lead Tech, Advanced Coagulation Lab
Rochester General Hospital

Hello, Mary Ann, and thank you for your question. I’ve sent it on to some of the folks at Siemens for clarification and have waited a couple of days, but have received no response so far. I’m frankly surprised Seimens advised you to adjust the results, as the reagent was apparently deteriorating. I will post their response as soon as I receive it.

Your approach to validating your PTT results over time is adequate and follows standard protocols of the CAP and CLSI. Do you have any reason to suspect the integrity of your control plasmas? Are you using Seimens’ controls? Though the problem appears to be reagent deterioration, you may wish to try controls from a different source, or even run some parallel controls for a brief period just to ensure your controls are working correctly. I will keep you posted if I have any further response to your question.

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