Platelet satellitism...

1. What is this phenomenon called and what is its definition?
   Platelet satellitism (also known as platelet satellitosis or platelet rosette) Platelet satellitism (also known as platelet satellitosis or platelet rosette).
   Defined as the adherence of four or more platelets to the surface of a segmented neutrophil, band, or monocyte.
   
2. What causes it?
   
   It is an artifact seen in EDTA peripheral bloods specimens. EDTA alters the conformation of the GPIIb/IIIa complex on the platelet surface, thereby facilitating IgG antibody attachment. The coated platelets then non-specifically attach to the surface of neutrophils (usually segs and bands, but rarely monocytes as well).
   A small amount of satellitosis, much less than in EDTA, has been observed with other anticoagulants and in non-anticoagulated blood as well.
3. What is the clinical significance?
   
   Platelet satellitism has been seen in any age; although some patients may be asymptomatic, the finding has been reported in a variety of clinical conditions, such as pregnancy, autoimmune disorders, Behcet’s disease, and thromboembolism. The amount of satellitosis has no association with the severity of clinical disease. Patients have been followed that have shown persistence of platelet satellitism for 15
   to 20 years.
   The danger in NOT identifying this phenomenon, is the inaccurate reporting of a spurious pseudothrombocytopenia. This can result in undue diagnostic testing, cancellation of surgery, unnecessary surgery (splenectomy), or even platelet Transfusion!
   
4. Is this patient's platelet count accurate?
   
   Probably not, depending on the delay of testing from time of specimen collection. Satellitosis occurs greatest at room temperature or colder, maximizing at 60 minutes. The effects may even be eliminated if samples are kept at 37 degrees C (keep warm from time of draw and deliver immediately to hematology for testing).
   
5. What will be the Sysmex flagging?
   
   The Sysmex sees this “cell” with the attached platelets as a normal neutrophil or Monocyte. No specific flagging will always be seen; it is possible to see transient Morphology flags (IG or PLT CLUMPS), but will not be consistent. So, it is possible to report out a “normal” platelet count and not be aware of the platelet satellitosis that is present.
   
   Your biggest “hint” to picking this up in an otherwise normal CBC would be if you see a significant fluctuation in the platelet count from draw to draw and/or you have a Delta flag in Cerner on your PLT. Check previous results for shifts or trends; depending again on delay in time of testing from time of collection and specimen temperature, each “satelliting”platelet count can give a unique result.
   
6. How can I obtain an accurate platelet count?
   Ideally, if the patient is known to demonstrate this phenomenon, collecting a specimen in citrate and correcting for the 9:1 blood:anticoagulant ratio (i.e. multiply citrate PLT by 1.1) will give an accurate count; ofcourse; review a PB smear of the citrate specimen to make sure the phenomenon is absent.
   
   If the patient has already been drawn, try warming the specimen at 37oC for 15 minutes and retesting immediately, while still warm. The platelets may detach from the neutrophils. Another option is to find another anticoagulated tube drawn on the patient at the same time that is NOT EDTA and has not been centrifuged. Confirm results by reviewing a stained PB smear of that anticoagulant. A manual fingerstick PLT count on a hemocytometer can also be done if the specimen is taken directly from the finger into the unopette pipet and then placed into the unopette reservoir. Remember to make a PB smear from the fingerstick as well to confirm the manual PLT count. (Usually it is easier on the patient and more accurate to redraw the patient venously for a citrated specimen.)
   For an outpatient, alert the physician to the finding and the inaccuracy of the PLT count. He may just need a qualitative PLT result (i.e. “adequate”) and this can be reported of your estimate confirms such. But, in cases of strong satellitism, it may be difficult to verify the adequacy of the PLT count. Always consult your hematology lead and/or pathologist for assistance. And let the physician know of the phenomenon and that the patient may present with this over a period of time.
   
7. To get an accurate platelet count, can I vortex the EDTA and/or do a manual hemocytometer platelet count?
   
   NO, vortexing the EDTA will introduce microbubbles that could be counted as PLTs. This would increase the PLT count but not necessarily verify accuracy.
   You will see the same platelet satellitism in the hemocytometer when doing the count from the EDTA tube; the platelets will not disassociate from the neutrophils in the unopette reservoir.
   
   
8. What other phenomenon can I see when satellitism is present?
   
   It is a rare event, but it is possible to see phagocytosis of platelets by the neutrophils or monocytes as well. It is also possible to see the phagocytosis without the satellitism. So, the bottom line is to very carefully and thoroughly review your PB smear For ALL abnormal findings when questioning an analyzer flag (remember, flagging can be more sensitive than specific, so look at everything) and when verifying a delta failure and/or a very abnormal result.

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