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Coagulation Corner

Tuesday, January 3, 2017

Commonly Asked Coagulation Questions!

Written By Donna Castellone, MS, MT (ASCP) SH | LinkedIn

I am asked many questions in coagulation, so I thought to start off the new year, I would share some of the most commonly asked questions and my thoughts.

1. Do you run a calibration curve every time you run a factor assay?

In the olden days (which was not so long ago), this wasn't even a question, it was a standard. There was no such thing as running a factor assay without creating a calibration curve. As coagulation became more automated, and reagents more optimized practices moved to using stored curves. This works well in PT based assays, however, over the years when I have been troubleshooting factor assays, and looked at what seemed to cause the most problems and rerunning of controls and ultimately and new curve, we were wasting reagents, money and most importantly time, it was decided to always making a curve for factor IX, since this seemed to give us the most problems. After several months, it seemed to produce better outcomes to always make a curve for factor VIII, and XII, well XII just needs that curve. So, with all of the troubleshooting, (regardless of controls being within limits), we would see issues when we ran shipment to shipment correlations, or one level of control being in, and the other being out of range. We were spending way longer time then just actually running a new calibration curve, which is just a point and click event. This seems to decrease our troubleshooting efforts and helps to ensure optimal results.

I would look at your processes within your laboratory, considering your instrument reagent combination, as well as repeatability and determine if this may actually benefit your laboratory and your patients.

2. When running platelet aggregations, do you use the patient's platelet poor plasma or do you dilute with buffer, what platelet count do you run your aggregations at?

We use the patient's platelet poor plasma if we need to make a dilution and standardize the platelet count between 280-320,000. One of the issues we have had is having very rapid aggregation in our controls. Initially we suspected an excess of platelets, but we checked our platelet poor plasma, and it had counts of < 10,000. We noted if we spun the platelet poor plasma for 30 minutes, we eliminated the problem. It may have been due to the interference of lipids in the plasma. It is preferred if patients could fast or have a light meal prior to platelet aggregation testing, but we have not had success in controlling that, however the 30 minute spin eliminated the interference.

3. Do you perform an incubated mixing study, and how do you determine a correction?

Our laboratory does perform an incubated mixing study. They also perform the study incubated separately and together to cover all possible interferences. I will admit, this was the practice when I came to the laboratory, and I have never seen a difference in results. A correction is based on the Rosner Index.

The Rosner Index subtracts the clotting time of the pooled normal plasma (PNP) from the clotting time of the 1:1 mix. This result is then divided by the clotting time of the patient sample. The equation is as follows:

    Rosner Index = (1:1 mix clotting time result - PNP clotting time result) / initial prolonged clotting time of patient sample

With this method, a high index value represents the possibility of an inhibitor. A low index value would represent a possible factor deficiency. For example, an index of 10 or lower indicates correction, 15 and above indicates no correction.
Our mixing studies are interpreted by our director and reported with comments.

4. How do you test for the DOACs?

Presently, the only information we can provide to clinicians is a trough level; that is the absence of a DOAC. The laboratory is in the process of setting up testing for DOACs, however none of these tests are FDA approved. As per New York State requirements, the test must undergo a complete validation and be submitted for approval, so more to follow. But there are calibrators and controls that are available to laboratories, in particular for the Xa based DOAC's you use your anti-Xa assay with the respective calibrator and control.

5. What is the best coagulation analyzer?

Simple and short answer, whatever works the best in your laboratory for your staff and patient population. While many analyzers have lots of bells and whistles- will you use them? Is your staff comfortable with new technology? Or will that really impact training and utilization? What about reagents? Can the company sequester a lot of PT/aPTT reagents, and will they last for at least a year, or longer than that. You don't want to be revalidating reagents more frequently. What about the types of reagents they offer? Do you want lupus insensitive, heparin sensitive? How sensitive? You are not just purchasing an analyzer, but their reagent system also. Anything else that is placed on the analyzer that doesn't come from the same company needs a robust validation, since you are modifying the test (the FDA approval for the test was given on another testing platform). All of this needs to be understood and reviewed prior to entering into a relationship with an analyzer. Trust me, many of those relationships are love/hate!

6. Where do you think the future of coagulation is going? Who will be our teachers for laboratory medicine?

The future of coagulation is very exciting. It is incorporated into cardiology, immunology, complement, sepsis, molecular with links to just about every discipline. There has been more discoveries in coagulation in the last 20 years - testing for Protein C, S, APCR, molecular testing, new anticoagulants just to name a few! I imagine somewhere someone will develop and make user friendly whole blood coagulation assays that incorporate all cellular elements and mimic what happens physiologically - user friendly being the optimal word.

The teachers for laboratory medicine are you! You are out there, just take what you know and pass it on, many things can't be learned in a book, but are learned standing in front of an analyzer and asking the question, WHY does that result seem strange? What if I test this? Or make a dilution? Coagulation is not just a science but also an art, it is an investment. So take the time to invest in someone, whether it be yourself or the technologist who has an interest.

All the best in 2017!



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