Platelet Clumping in Sodium Citrate and Plateletpheresis

An interesting question from Mary Coleman at the University of North Dakota:

A female student reported to student health with a severe headache. She had a complete blood count performed using a standard EDTA tube and she had a low platelet and elevated lymphocyte count. The laboratory scientist also prepared a direct blood film from the needle. On the film the patient’s platelet estimate was normal and her platelets and lymphocytes were distributed normally.

For a follow-up collection the scientist used a syringe and transferred the blood to both an EDTA and a sodium citrate tube. She immediately ran a sample from the EDTA tube and the platelet count was normal. Several minutes later a repeat count on the EDTA and citrate tube showed that the platelet count had dropped and the lymphocyte count went from 29 to 46%. I would guess the patient has a cold platelet antibody, and the platelet clumps were being counted as lymphs.

But my question is, this student had been providing plateletpheresis donations. Should she be advised to discontinue pheresis, since the blood goes from body temperature to room temperature, and also, could something in the pheresis process stimulated her immune system to produce platelet antibodies?

Thanks, Mary Coleman

Mary, thank you for your questions. The platelet clumping you describe is probably the result of the same family of antibodies that causes platelet satellitosis, the condition in which platelets immunologically bind the membranes of neutrophils. These antibodies are EDTA-dependent, though they sometimes cause clumping in 3.2% sodium citrate tubes, and they are not temperature-dependent. In this case, the antibody causes in vitro platelet clumping instead of satelliting.

I referred this question to my wife and immunohematology consultant, Margaret Fritsma, MA, MT (ASCP) SBB who reports there is nothing in the AABB standards about platelet donors who are documented with platelet satellitosis. Because pheresis products are collected using acid citrate dextrose (ACD), they may not clump. When EDTA and sodium citrate tubes are associated with satellitosis, we sometimes use ACD tubes to provide an accurate platelet count.

Further, before, during, or after pheresis a platelet count is performed, which, if reduced, would reveal the existence of satellitosis and prevent or terminate the collection. Platelet satellitosis would not affect red blood cell donor products, but could be a concern in single (random) donor platelet concentrate collection, a process that is being largely replaced by plateletpheresis. Single donor platelet concentrates may not be counted prior to use.

I doubt the citrate used in plateletpheresis would trigger an immune response. I hope this helps. I plan to give platelets again on Thursday, April 2 and will ask the technicians this question. If I learn anything new, I will post it here. Geo.