Haematologica vo l. 84(7): J uly 1999 Haematologica 1999; 84: 655 t he i rrepl aceabl e imag e Anticoagulant pseudothrombocytopenia with platelet satellitism MONICA MORSELLI , G IUSEPPE L ONGO, G ORETTA BONACORSI , L EONARDO P OTENZA, G IOVANNI E MILIA, GIUSEPPE T ORELLI De partment of Medical Sciences , Section of Internal Medicine, Oncology and Hae matology, Univ ersity of Modena and Reggio Emilia, Italy Correspondence: Giuseppe Longo, Dipartimento di Scienze Mediche, Oncologiche e Radiologiche, Sezione di Medicina Interna, via Del Poz- zo 71, 41100 Modena, Italy. Phone: international +39-059-422782 – Fax: int ernational +3 9-05 9-4 245 49 – E- mail: longo@ unimo.i t aware that some thrombocytopenias of uncertain etiology may be artifactual in particular conditions; spurious thrombocytopenia due to EDTA-induced pl atelet s atell it ism is an e x ample of s uch a phenomenon. References 1. S hahab N, E va ns ML. P latelet s atellit ism. N E ngl J Med 1998; 338:591. 2. P eters MJ , Heyderman RS , Klein NJ . Plat elet satellitism. N Engl JMed 1998; 339:131-2. 3. S hahab N, E vans ML. P lat ele t satelli t ism. Authors R eply. N E ngl JM e d 1998; 339:131-2. 4. Bizz aro N, Gol dschmeding R, von dem Borne AE . Platelet satellitism is Fc RIII (CD16) receptor-medi- ated. Am JClin Pathol 1995;103:740-4. 5. Christopoul os C, Mat t ock C. P lat e let s atelliti sm and -granule proteins. JClin Pathol 1991;44:788-9. T here has been a discussion recently in the liter- ature about platelet-leukocyte interactions in vivo and their well recognized importance in modulating inflammation and hemostasis. Occa- sionally, and only under particular conditions, plat e lets may int e ract wi th polymorphonuclea r neu- tr ophil s forming complex e s that may le ad t o a spurious thr ombocy tope nia. 1-3 We obse rve d a 35-ye ar old healthy man in whom repeated routine laboratory tests showed a mild thrombocytopenia (70- 90,000 / mm 3 ). The blood film revealed scattered platelet rosetting around polymorphonuclear neu- t rophil s ; t he phenome non was e vide nt onl y whe n the blood was treate d wi t h EDT A as a nt icoagulant and incubated at room temperature (Figure 1). A blood ca pil lary ﬁlm pe rfor me d wi thout E DTA did not rev e al platelet satellitism and the direct count using capil- lary blood with ammonium oxalate was normal. Of int ere s t , pl atele t s atellit ism with p olymorphonuclea r eosinophils or basophils, was never observed (Figure 2) . Ros e t t ing was not e vide nt whe n cit rat e or heparin was used. Platelet phagocytosis by monocytes was sometimes seen. In this case, the in vitro interaction between platelets, neutrophils and EDTA was the likely cause of the spurious thrombocytopenia. The me chanis m of plat e let sate llitism is not com- pletely understood. Ig autoantibodies dir e ct agains t the gly coprot e in I Ib/ IIIA complex of t he plate lets a nd the Fc ( ) receptor III (Fc RIII) of neutrophils have been implicated. EDTA at low temperature might alter the conformation of platelet glycoproteins and ne ut rophi ls F c rec e pt or by che lati on o f calc ium ions. Bridge for mati on betwee n plat e lets a nd neutrophil s may t ake place t hrough t he binding of t he F ab fr ag - me nt t o t he IIb/ IIIa pl atele t glycoprot ein and the F c fragment to the Fc RIII of the PMNs. Alternatively, but less likely, autoantibodies may recognize the s ame epi t ope in t he t wo struct ures. 4 A non-immuno- logic mechanism has also been proposed involving thrombospondin (or other -granule proteins such as P-selectin) that, when an activation stimulus is present, is rapidly expressed on platelet surface favor- ing adhesion to neutrophils. 5 Physicians should be Figure 1. Platelet satellitism around 2 neutrophils. Figure 2. Platelet satellitism around the neutrophil but not around the eosinophil.

Platelet Satellitisim

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Haematologica vol. 84(7): July 1999

Haematologica 1999; 84:655 the irreplaceable image

Anticoagulant pseudothrombocytopenia with platelet satellitismMONICA MORSELLI, GIUSEPPE LONGO, GORETTA BONACORSI, LEONARDO POTENZA, GIOVANNI EMILIA,

GIUSEPPE TORELLI

Department of Medical Sciences, Section of Internal Medicine, Oncology and Haematology, University of Modena and Reggio Emilia, Italy

Correspondence: Giuseppe Longo, Dipartimento di Scienze Mediche,Oncologiche e Radiologiche, Sezione di Medicina Interna, via Del Poz- zo 71, 41100 Modena, Italy. Phone: international +39-059-422782 – Fax: international +39-059-424549 – E-mail: [email protected] t

aware that some thrombocytopenias of uncertainetiology may be artifactual in particular conditions;spurious thrombocytopenia due to EDTA-inducedplatelet satellit ism is an example of such a phe-nomenon.

References

1. Shahab N, Evans ML. Platelet satellit ism. N Engl JMed 1998; 338:591.

2. Peters MJ, Heyderman RS, Klein NJ. Platelet satel-litism. N Engl JMed 1998; 339:131-2.

3. Shahab N, Evans ML. Platelet satelli tism. AuthorsReply. N Engl JMed 1998; 339:131-2.

4. Bizzaro N, Goldschmeding R, von dem Borne AE.Platelet satellitism is Fc RIII (CD16) receptor-medi-ated. Am JClin Pathol 1995;103:740-4.

5. Christopoulos C, Mattock C. Platelet satellitism and-granule proteins. JClin Pathol 1991;44:788-9.

There has been a discussion recently in the liter-ature about platelet-leukocyte interactions in

vivo and their well recognized importance inmodulating inflammation and hemostasis. Occa-sionally, and only under particular conditions,platelets may interact with polymorphonuclear neu-trophils forming complexes that may lead to a spuri-ous thrombocytopenia.1-3 We observed a 35-year oldhealthy man in whom repeated routine laboratorytests showed a mild thrombocytopenia (70-90,000/mm3). The blood film revealed scatteredplatelet rosetting around polymorphonuclear neu-trophils; the phenomenon was evident only when theblood was treated with EDTA as anticoagulant andincubated at room temperature (Figure 1). A bloodcapillary film performed without EDTA did not revealplatelet satellitism and the direct count using capil-lary blood with ammonium oxalate was normal. Ofinterest, platelet satellit ism with polymorphonucleareosinophils or basophils, was never observed (Figure2). Rosetting was not evident when citrate or heparinwas used. Platelet phagocytosis by monocytes wassometimes seen. In this case, the in vitro interactionbetween platelets, neutrophils and EDTA was thelikely cause of the spurious thrombocytopenia.

The mechanism of platelet satellitism is not com-pletely understood. Ig autoantibodies direct againstthe glycoprotein IIb/ IIIA complex of the platelets andthe Fc () receptor III (FcRIII) of neutrophils havebeen implicated. EDTA at low temperature mightalter the conformation of platelet glycoproteins andneutrophils Fc receptor by chelation of calcium ions.Bridge formation between platelets and neutrophilsmay take place through the binding of the Fab frag-ment to the IIb/ IIIa platelet glycoprotein and the Fcfragment to the FcRIII of the PMNs. Alternatively,but less likely, autoantibodies may recognize thesame epitope in the two structures.4 A non-immuno-logic mechanism has also been proposed involvingthrombospondin (or other -granule proteins suchas P-selectin) that, when an activation stimulus ispresent, is rapidly expressed on platelet surface favor-ing adhesion to neutrophils.5 Physicians should be

Figure 1. Platelet satellitism around 2 neutrophils.

Figure 2. Platelet satellitism around the neutrophil but notaround the eosinophil.