From Mahnaz Sairi, Hello, George. We use pooled normal control plasma (PNP ) from George King and lately found out that mixing buffer with PNP and using that as a control is confusing our physicians. Because they are asking why the control results are increasing? I really do not know why we are diluting the plasma with buffer. Can you please help?
This is from our procedure manual:
- Run APTT on normal control plasma and patient plasma.
- Mix control plasma(pool plasma) 1:1 with Koller Buffer.
- Mix patient plasma 1:1 with control plasma (pooled plasma).
- Run APTT on the two mixtures.
- Incubate remainder of the mixtures for 2 hours, 37C in a water bath.
- Repeat APTT on both incubated specimens.
Hello, Mahnaz Sairi, and thank you for your question. I know of no reason for preparing a dilution of the PNP. Both the immediate and the two-hour incubated mix result should be compared with the undiluted PNP. When performing the two-hour mixing study, the PNP is incubated alongside the mix so that you can compare the mix result with the incubated PNP.
There is a modification of the mixing study called the "saline mix." In this approach, in addition to the PNP mix, you can prepare a separate 1:1 patient plasma, buffered saline mix. Here is a quote from the 2002 Esoterix Coagulation Coagulation Handbook.
"If the PTT result obtained with the immediate PNP-patient plasma mix corrects and the saline mix result is prolonged dramatically, a factor deficiency or specific factor inhibitor is suspected. With factor deficiency, heparin, or a specific factor inhibitor, the 1:1 saline mix shows significant prolongation. If the result of the immediate PNP-patient mix shows only partial or no correction, and the result obtained with the saline mix shows near correction, then lupus anticoagulant is suspected."
I don't know of many who perform the saline mix, though at Esoterix Coagulation we found it helped resolve euivocal results.
Back to your question, I invite our participants to provide your mixing study experience. Do you know of instances where it makes sense to dilute the PNP ? Also, have you ever used the saline mix? Thank you.