Isolated case of platelet satellitism around white blood cells and phagocytosis by neutrophils and monocytes.

INTRODUCTION: Rarely, platelets can interact with other blood elements, forming platelet aggregates. This paper presents an isolated case of platelet satellitism around neutrophils, lymphocytes and monocytes with platelet phagocytosis by both neutrophils and monocytes. CASE
PRESENTATION: The subject was an 89-year-old woman with breast cancer on anti-estrogenic hormone cancer therapy. Whole blood sample collected in a tube with EDTA (Ethylenediaminetetra-acetic acid) anticoagulant was analysed within 4 hours, using an XN haematology analyser (Sysmex). The CBC (complete blood count) presented the following results: WBC (White blood cell) 4.0 x 109/L, RBC (Red blood cell) 3.58 x 1012/L, haemoglobin 116 g/L, haematocrit 34.9%, MCV (Mean corpuscular volume) 97.5 fL, MCH (Mean corpuscular haemoglobin) 32.5 pg, MCHC (Mean corpuscular haemoglobin concentration) 33.2 g ⁄dL, RDW (Red blood cell distribution width) 14.6% and PLT (Platelet) 136.
CONCLUSION: This manuscript describes the platelet satellitism around neutrophils, lymphocytes and monocytes and the interesting, very rare and singular phenomenon of platelet phagocytosis by not only neutrophils but also monocytes.

Ethylenediaminetetra-acetic acid

White blood cell

Red blood cell

Mean corpuscular volume

Mean corpuscular haemoglobin

Mean corpuscular haemoglobin concentration

Red blood cell distribution width

Platelet

Gamma-glutamyltransferase

High-density lipoprotein

Low-density lipoprotein

Introduction

Rarely, platelets can interact with neutrophil polymorphs, forming platelet aggregates around the cytoplasm, an uncommon phenomenon called ‘platelet satellitism’ (PS). PS is an in vitro artifact thrombocytopenia due to the EDTA anticoagulant used for the collection of peripheral whole blood at room temperature. Although automated haematology analysers have evolved greatly, increasing the reproducibility and accuracy of platelet counts, they may not completely resolve pseudothrombocytopenia, which may mislead the clinician into unnecessary investigations and treatment [1]. To remedy this spurious cause of thrombocytopenia, a morphological review of the peripheral blood smear should be performed in all patients with thrombocytopenia. PS usually occurs around neutrophil granulocytes and only in extremely rare cases are platelets phagocytosed by neutrophils, forming rosettes around lymphocytes and monocytes as observed only in patients with neoplastic lymphocytes [2,3]. This paper presents an isolated case of platelet satellitism around neutrophils, lymphocytes and monocytes with platelet phagocytosis by both neutrophils and monocytes.

Case presentation

An 89-year-old woman with breast cancer and on anti-estrogenic hormone cancer therapy had a home collection and the whole blood sample collected in a tube with EDTA anticoagulant was analysed within 4 hours at the Clinical Chemistry Analysis Laboratory of the San Donato Hospital in Arezzo using an XN haematology analyser (Sysmex). The patient agreed to use the anonymised clinical data for research purposes. The complete blood count (CBC) presented the following results: WBC 4.0 x 109/L (reference interval 4.0-10.0), RBC 3.58 x 1012/L (reference interval 3.80-5.20), haemoglobin 116 g/L (reference interval 117-160), haematocrit 34.9% (reference interval 35.0-46.0), MCV 97.5 fL (reference interval 80.0-97.0), MCH 32.5 pg (reference interval 26.0-34.0), MCHC 33.2 g/dL (reference interval 32.0-36.0), RDW 14.6% (reference interval 11.6-13.7) and PLT 136 (reference interval 140.0-440.0). Other blood tests showed aspartate aminotransferase (AST) 32 U/L (reference interval 2-31), alanine aminotransferase (ALT) 38 U/L (reference interval 2-34), gamma GT 5 U/L (reference interval 9-40), total bilirubin 0.29 mg/dL (reference interval 0.50-1.20) with direct bilirubin 0.15 mg/dL (reference interval 0.00-0.25) and indirect bilirubin 0.14 mg/dL (reference interval 0.00-1.00), urea 0.86 g/L (reference interval 0.17-0.49), creatinine 1.51 mg/dL (reference interval 0.51-0.95), glomerular filtration rate (CKD-EPI) 30.4 mL/min/1.73mq (reference cut-off ≥60), uric acid 7.0 mg/dL (reference interval 2.0-6.6), calcium 8.5 mg/dL (reference interval 8.4-10.6), sodium 136 mmol/L (reference interval 136-146), potassium 5.0 mmol/L (reference interval 3.5- 5.2), total cholesterol 142 mg/dL (desirable cut-off <200), HDL cholesterol 86 mg/dL (desirable cut-off ≥60), LDL cholesterol 41 mg/dL (desirable cut-off ≥115), triglycerides 96 mg/dL (desirable cut-off <150), total protein 4.6 g/dL (reference interval 6.6-8.3), C reactive protein 0.2 mg/dL (reference interval 0.00-0.50), iron 55 μg/dL (reference interval 40-140), carcinoembryonic antigen 6.1 μg/L (reference interval 0.0-5.0), 25-hydroxy-vitamin D 15 nmol/L (<25 severe deficiency), thyrotropin (TSH) 8.12 mUI/L (reference interval 0.27-4.20), free thyroxine (FT4) 5.1 pmol/L (reference interval 12.00-22.00), and free triiodothyronine (FT3) 0.4 pmol/L (reference interval 3.1-6.8). In the chemical-physical examination of the urine, all parameters were normal except for the relative density of 1.014 kg/L (reference interval 1.016-1.024) and the leukocyte esterase value of 250 cells/μL (reference interval: absent), while in the microscopic examination of the urine, the presence of bacteria (reference interval: absent) and WBC 40 cells/μL (reference cut-off <15), squamous epithelial cells 8 cells/μL (reference cut-off <20) and hyaline cylinders 2 elements/μL (reference cut-off <2) was observed. Following the execution of a complete blood count (CBC), a microscopic review of the peripheral blood smear was performed for essentially two reasons: both for the suspicion of pseudothrombocytopenia, given the number of platelets discordant with the previous value and the rules of instrumental block of the sample for the verification of thrombocytopenia and the reflex of execution of (PLT-F) platelets in fluorescence; and due to instrumental alarms referring to the WBC differential fluorescence (WDF) scattergram such as ‘Lymphopenia’, ‘Positive Diff’, and ‘Positive Morph’ with superimposition of the neutrophil cluster with that of eosinophils (Fig. 1). A May-Grünwald stained peripheral blood smear review revealed platelet rosettes/satellitism around neutrophils (Fig. 2 a), lymphocytes (Fig. 2 c, d) and monocytes, with a noticeable finding of some phagocytosed platelets in the cytoplasm of neutrophils (Fig. 2 b), but especially within monocytes (Fig. 2 e, f, g).

Fig. 1

WBC differential fluorescence (WDF) instrumental scattergram following the execution of the complete blood count (CBC).

Fig. 2

Digital microscopy images. Platelet satellitism around neutrophils (a), lymphocytes (c, d) and phagocytosed platelets by neutrophils (b) and monocytes (e, f, g).

Discussion/conclusion

This paper describes platelet satellitism around the three types of cells, i.e. neutrophils, lymphocytes and monocytes, and the interesting and rare finding of platelet phagocytosis both the neutrophils and monocytes.

Platelet satellitism has been reported at any age; most of individuals are asymptomatic, and in various clinical states, such as pregnancy, autoimmune disorder, Behcet's disease, thromboembolism, chronic liver disease [4] and malignant disorders like mantle cell lymphoma [5]. There have been previous reports of platelet satellitism around neoplastic lymphoid cells [6], large granular lymphocytes [7] and monocyte-monocyte adhesion, satellitism and phagocytosis of platelets by monocytes without neutrophils being involved [3]. Although platelet satellitism is a rare cause of spurious thrombocytopenia, the haematologist should be aware of this in vitro phenomenon, which may be the underlying cause of pseudothrombocytopenia [4] in order to avoid unnecessary further investigation. Thus, recognition of this in vitro phenomenon re-emphasises the necessity to execute the traditional and reliable peripheral blood film examination [8].

Platelet satellitism was first described in 1963 by Field and MacLeod as an incidental finding observed in the workup of thrombocytopenia caused in vitro by EDTA anticoagulation of blood at room temperature. It has described in blood samples collected in EDTA only and not in anticoagulants like heparin, citrate, acid-citrate dextrose and ammonium oxalate [8]. In 1986, von dem Borne [9] introduced the idea of cryptantigens or hidden antigens; according to an immunological mechanism, these antigens occur exclusively on platelets, particularly on the membrane glycoprotein IIb/IIIa complex. These cryptantigens are normally not exposed on circulating platelets, but eventually exposed only when the platelet membrane pass through a conformational change as a result of Ca2+ ion removal by the chelator EDTA [10]. Immunoglobulin G autoantibodies are directed against the binding complex formed between glycoprotein IIb/IIIa of the platelet membrane and the neutrophil Fc gamma receptor. A non-immunologic mechanism has also been proposed, which claims that thrombospondin, or some other alpha‐granule protein, is expressed on the platelet surface, facilitating adhesion to neutrophils in response to different processes [1].

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or. not-for-profit sectors.

Declarations of competing interest

None.