Pseudothrombocytopenia

From Dr. Bruce King: I had a question about options for analyzing a patient sample that the platelets clump in all anticoagulants tested.

We have a 61 y.o. female who was hospitalized for hypertensive issues and noticed some bruising (abdomen) which the patient said had increased over the last several weeks. During the hospitalization it was noted that she had thrombocytopenia (90s) with clumps seen on the smear. They diagnosed pseudothrombocytopenia but did an “extensive workup” at an outside facility with no abnormalities found. The patient was noted to be vitamin B12 deficient though. She saw a local hematologist for second opinion and the platelets were still clumped in EDTA and also citrate tubes. The hematologist was concerned that she may be dealing with ITP and gave her steroids and her platelet count jumped from 20s to 40s but quickly went back down within a week or two. We also tried heparin and vortexing the specimens with all anticoagulants showing clumps and low platelet count in the 20s–30s. Although the platelets were clumped, the estimate appeared decreased as well in the range of maybe 50K. There were large platelets noted. Her IPF was 17.9 also. I would like to see if you or your contacts would have any other suggestions on how to evaluate this platelet’s issue. Any assistance or insight is most welcome.

Hello, Dr. King, and thank you for your message, which I’ve shared with several colleagues. My initial response is to agree that this is likely ITP given her bruising pattern, response to steroids, and large platelets. Here is a reply from Dr. Emanual Favaloro:

Hi George, I am not an expert in this area, but the clinical features are suggestive of ITP (bruising and presence of large platelets suggesting early release/turnover). Also, my limited understanding is that pseudothrombocytopenia would not be expected with multiple anticoagulant tubes (EDTA and citrate in this case) – have they tried oxalate tubes? Finally, my Italian colleague Giuseppe Lippi has suggested one last thing to help rule out pseudothrombocytopenia, that is whether blood samples (in citrate) have also been maintained at 37°C before testing. They have seen some cases of temperature-dependent anti-platelet antibodies, becoming active at temperatures <15–20°C. But yes, my vote is with some sort of in-vivo auto-immune/antibody related platelet clumping and clearance.
cheers, Emmanuel Favaloro.

I also spoke with colleague Dave McGlasson, who referred me to a current publication: Zhang L,Xu J, Gao L, Pan S. Spurious thrombocytopenia in automated platelet count. Laboratory Medicine 49:2:130–3 DOI: 10.1093/labmed/lmx081. In our discussion we were especially curious about Dr. Lippi’s observation, which could imply a form of thrombocytopenia analogous to cold autoimmune hemolytic anemia. Dave asks, “Could you post a question to learn if anyone has ever looked at platelet counts and clumping on specimens that have been incubated at 37°C when looking at cold agglutinins or for any other reason to incubate EDTA specimens. I can’t find any references to this issue.”

Later on April 26, 2018 from Dr. Larry Brace: “I have seen a case in which blood collected in EDTA, citrate and heparin had platelet clumping. We even tried keeping the blood samples at 37°C from blood draw to sample aspiration into the cell counter. So we went “old school” and made a blood smear from a finger stick. We did not see platelet clumps on this smear and did a platelet estimate from the smear. While it was not a platelet “count” it did give a reasonable estimate. In our case the platelet estimate was ‘adequate.'”

Please continue to watch this entry, as we continue to solicit responses. Dave also asked to see the rest of the CBC parameters.