CASE REPORT |
https://doi.org/10.5005/jp-journals-11003-0123 |
Platelet Satellitism: A Rare In Vitro Phenomenon Causing Spurious Thrombocytopenia
Department of Pathology, Army College of Medical Sciences, Delhi, India
Corresponding Author: Sharmila Dudani, Department of Pathology, Army College of Medical Sciences, Delhi, India, Phone: +91 9811778156, e-mail: drsdudani@hotmail.com
Received on: 25 April 2023; Accepted on: 16 May 2023; Published on: 28 June 2023
ABSTRACT
Platelet satellitism is the adherence of platelets around leukocytes (mainly neutrophils, but occasionally seen around lymphocytes and monocytes). It is a rare and important in vitro cause of spurious thrombocytopenia and may lead to unnecessary further investigations in patients. It usually occurs with ethylenediaminetetraacetic acid (EDTA) anticoagulated blood and is not seen with other anticoagulants. It may be seen in a variety of diseases as well as in normal individuals. Both immunological and nonimmunological mechanisms are believed to play a role. Platelet morphology and function are usually normal. We report a case of a 34-year-old female who underwent a complete blood count (CBC) as a part of a routine health checkup. As platelet satellitism was recognized on examining the peripheral smears, it highlights the importance of the same for confirmation.
How to cite this article: Dudani S. Platelet Satellitism: A Rare In Vitro Phenomenon Causing Spurious Thrombocytopenia. J Med Acad 2023;6(1):31-32.
Source of support: Nil
Conflict of interest: None
Patient consent statement: The author(s) have obtained written informed consent from the patient for publication of the case report details and related images.
Keywords: Ethylenediaminetetraacetic acid, Thrombocytopenia, White blood cells
INTRODUCTION
Platelet satellitism is a rare, unusual, and interesting in vitro phenomenon seen in peripheral blood smears prepared from EDTA-anticoagulated blood, wherein platelets are seen adherent to the surface of neutrophils, imparting a rosette-like appearance around neutrophils, known as “platelet satellitism.”1 Platelet morphology and function are normal. The reason for this is not completely understood, but immune and nonimmune mechanisms are believed to play a role.2,3
As blood samples for routine hematological investigations, including platelet counts, are collected in lavender-top vacutainers containing EDTA as an anticoagulant, awareness of this phenomenon and its recognition is important to avoid the misdiagnosis of thrombocytopenia by the clinician, which may lead to unnecessary further investigations for the patient or delay in surgical treatment. We report a case of a 34-year-old female whose blood sample was collected for a routine health checkup.
CASE DESCRIPTION
A 34-year-old female had basic laboratory investigations done during a routine health checkup. Blood was collected by venipuncture during home collection by a trained phlebotomist using a closed vacutainer system in lavender-capped EDTA vacutainers. The sample was transported to the laboratory in an icebox at 4°C and analyzed within 4 hours of collection in a fully automated five-part cell counter, per the manufacturer’s instructions (Horiba Yumizen 1500, Japan). CBC findings were as follows: hemoglobin—10.6 gm%; red blood cell count—3.62 × 106/mm3; hematocrit test—32%; mean corpuscular volume—88.3 fL; mean corpuscular hemoglobin—29.3 pg%; mean cell hemoglobin concentration—33 gm%; and white blood cells count—3.42 × 103/mm3. The differential count showed neutrophils—60.8%; lymphocytes—29.9%; eosinophils—0.8%; monocytes—8.5%, platelet count—102 × 103/mm; mean platelet volume—12.6 fL; plateletcrit—0.129%; and platelet distribution width—29 fL. As the CBC report showed thrombocytopenia, a reflex peripheral smear was prepared and stained manually with Leishman stain and observed under a light microscope (Olympus Magnus MLX Plus), which revealed platelet adherence on the surface of neutrophils (Fig. 1). It was not observed on the surface of lymphocytes, eosinophils, or monocytes. Platelet morphology appeared normal on the peripheral smear. The patient did not suffer from any ailment (either acute or chronic) and did not report any drug intake except for multivitamin supplements. Repeat samples in a different vacutainer could not be collected.
Fig. 1: Platelets seen adherent around the surface of a neutrophil in the form of a rosette Leishman stain, 40X
DISCUSSION
Platelet satellitism was first described by Field and Macleod in 1963, and since then, approximately only 100 cases have been described in the literature.4 It has been described exclusively in tripotassium-EDTA mixed blood, not when direct smears are made, or when other anticoagulants like double oxalate, sodium citrate, heparin, or acid citrate dextrose are used.5 The addition of 20 mg/mL of kanamycin to EDTA-anticoagulated blood has shown dispersion of platelets.6 Though platelet satellitism has been frequently described to occur around neutrophils, it has also been observed around basophils, eosinophils, lymphocytes, and monocytes,7 platelet function is usually normal.
Platelet satellitism has been observed in patients with urinary tract infections, vasculitis, mantle cell lymphoma, lupus, thrombocytopenic purpura, chronic alcoholism, cryofibrinogenemia, squamous cell and hepatocellular carcinoma, pregnancy, and even in healthy individuals.8 Though the mechanism of platelet satellitism is not fully understood, both immunological and nonimmunological mechanisms appear to play a role. It is believed that autoantibodies directed against the following antigenic proteins, namely, the glycoprotein IIb/IIIa complex on the platelet and neutrophil FcgRIII receptor may play a role. These autoantibodies are present naturally in some individuals. It is also postulated that EDTA anticoagulant may expose some cryptic epitopes which are otherwise sequestered. Alternatively, thrombospondin or P-selectin is expressed on the platelet surface, favoring adhesion to neutrophils through a nonimmunological mechanism.8 It is unknown if any drug intake can cause this phenomenon.
Though the platelets appear to be only adherent on the surface of neutrophils, Lorubbio and Ognibene reported platelet satellitism around neutrophils, lymphocytes (both normal and even atypical), and monocytes and the phagocytosis of platelets by neutrophils and monocytes.9 The phenomenon is largely temporary; it has occasionally been reported in an elderly patient hospitalized for urinary tract infection, even 3 weeks after discharge.8 Platelet satellitism, when observed under electron microscopy, revealed varied associations between the two cells. In most instances, focal areas of contact between the apposing limiting plasma membranes of the platelet and neutrophils were seen. Occasionally, contact occurred via a pseudopod from the neutrophil, whereas in other instances, it involved a short process coming out from the platelets. Rarely, platelets appeared to be completely or partially enclosed within the phagocytic vacuoles of a neutrophil.10
The awareness and recognition of this phenomenon are important as it highlights the importance of the age-old practice of examining peripheral blood smears in the era of automation.
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