Platelet Counts on Platelet Rich Plasma samples

[rickraley]

:wink:

I asking for the best protocol/technique for acquiring a platelet count for platelet rich plasma samples. I was recently left without a reason why four samples sent for analysis were returned with four extremely different platelet counts. The four samples were all from the same 5cc sample. Two analysis' used a 4:1 dilution technique and the other two were direct aspiration. All four samples should have yielded at least a 3X baseline but did not. The fifth sample sent from the same batch, analyzed without dilution yielded a 8X baseline which was very close to our calculated goal.

I don't usually question the results but I would like to know if there is a best way to do this, as I am not a lab guru and I don't want to go back to counting them by hand.

Thanks!

-Rick

[Deb]

Rick, A lot of things can go wrong with counting platelet rich plasma. What type of tubes were being use, polypropylene plastic is the best. On occasion EDTA can cause aggregation of platelets in whole blood samples, I'm sure the same can happen in PRP. Are they using a liquid or dry EDTA? We don't dilute our PRP any longer because our hematology instrument has a high enough linearity...and any dilution step can lead to error. We also require that the specimens are well mixed; to ensure this they allow them to gently rock a minimum of 10 minutes on a tube rocker and then sample them immediately. Check you hematology instrument/manufacturer, does it count by impedence or optical method. We recently did a study with our Sysmex and found out that the optical method would at times give a count that was 30% higher than the impedence count.....but the impedence count was most accurate when validated against manual chamber counts. There is now a CAP proficiency kit for counting platelet rich specimens which I have asked our hematology lab to subscribe to as PRP is way different that WB.Deb

[rickraley]

Deb,

Thanks your reply has given me some help when I ask my lab guru's. I want to try to speak their lingo when I attempt to ask those questions.

Much obliged!

Much obliged!

[cmelloh]

I am getting ready to start validation a LH 750 and DxH, both Beckman-Coulter, for platetet counts on platelet rich plasma. I have a few questions. Is there a certain amount of time that should elapse between the PRP sample being collected and the sample analyzed? How often should linearity for PRP be performed? We remove 3mL of PRP from our plateletpheresis product, place the sample in EDTA, and refrigerate. Is this the best storage option or should the samples be kept at room temp? Thanks!

[heathervaught]

Once the sample is in the tube, I would allow it to rock for several minutes (see the previous post), but test it as soon as possible, and at room temp (not refrigerated!). As for the tube type, whatever is going to be used in your routine is what you should use for your validation. I would also recommend waiting at least 24 hours from when the products are collected to obtain the samples. You will find that samples from "fresh" products will have lower platelet counts than those allowed to relax for a time period prior to sampling (we noticed this when we went from sampling for counts on Day 0 to Day 1).

[cmelloh]

We allow our products to "rest" for one hour after collection and the rock for another hour before sample collection. By allowing the platelet to relax, does this cause any microaggregates to dissolve causing an increase in the platelet count? If so, would vortexing the sample give the same result or would it activate the platelets making the counts even lower?

[Gnapplec]

Our SOP requires us to sample our platelet pheresis before 24 hours post collection. We run them through our analzyer as soon as we collect our sample. We do not let them set overnight in tubes or store them at room temp for more than an hour. I wouldn't imagine that vortexing would be a good idea but I'm just guessing.