ous leukocytosis in complete blood counts (CBC) performed with routine hematology analyzers [2â4]. Clinical needs and current analytical goals demand ...
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Laboratory Hematology 4:225–226 © 1998 Carden Jennings Publishing Co., Ltd.
#98-15 Lippi
Official Publication
LETTER TO THE EDITOR
Accurate platelet count avoiding platelet clumping G. LIPPI,1 R. FACCHINETTI2 1 2
Istituto di Chimica e Microscopia Clinica, Università degli Studi di Verona, Verona, Italy Laboratorio di Chimica Clinica e di Ematologia, Ospedale Civile Maggiore, Azienda Ospedaliera di Verona, Verona, Italy
In a previous article, Bowen et al. reported sensitivity and specificity of instrument flags for platelet clumping on Abbott CELLDYN 4000 and Coulter STKS hematology analyzers [1]. Platelet clumps in vitro usually induce pseudothrombocytopenia and spurious leukocytosis in complete blood counts (CBC) performed with routine hematology analyzers [2–4]. Clinical needs and current analytical goals demand accurate and precise platelet and leukocyte counting to avoid inappropriate therapeutic decisions. Bowen et al. confirmed true or false platelet instrumental counts by review of microscopic smears; however, this procedure is inadequate to obtain accurate platelet counts, particularly in the presence of true platelet clumps [1]. Some expedients were proposed to prevent platelet clumping in vitro, mainly based on the use of alternative non-EDTA anticoagulated whole blood [3]; however, those solutions are usually unsuitable for CBC. We earlier proposed an anticoagulant-antiaggregant mixture (citrate–pyridoxal phosphate–Tris or CPT) that proved effective in preventing platelet clumps, thus allowing accurate CBC on most hematology analyzers [5–7]. Recently, platelet counts were found to be higher in CPT-treated samples compared with EDTA-anticoagulated whole blood using the Abbott CELL-DYN 3500 automated hematology analyzer [8]. This observation is really not unexpected, as it is conceivable that the platelet count obtained in normal samples of CPT-anticoagulated blood may be more accurate than suboptimal blood collection techniques in which traumatic venipuncture or delayed mixing with EDTA often might induce spontaneous platelet clumping in vitro. Possible mechanisms justifying the pyridoxal-5-phosphate–dependent inhibition of both platelet reaction and aggregation were earlier postulated by Lam et al. [9]. To corroborate those findings, we investigated platelet function after 5-
FIGURE 1. Representative closure times of apertures in membranes coated with collagen and ADP (a1, a2) or collagen and epinephrine (b1, b2) by normal platelets collected from healthy donors with (a2, b2) or without (a1, b1) 1.0 mmol/L pyridoxal-5-phosphate.
Address correspondence to Giuseppe Lippi, MD, Istituto di Chimica e Microscopia Clinica, Ospedale Policlinico, Via delle Menegone, 10, 37100 Verona, Italy. Received 29 June 1998; accepted 30 June 1998
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minutes preincubation of citrated whole blood with pyridoxal-5phosphate, using a novel system for rapid and accurate determination of platelet function in vitro (PFA-100, Dade Behring) [10]. After the preincubation with pyridoxal-5-phosphate, platelet aggregation was triggered by membranes coated with collagen and ADP or collagen and ephinephrine. As a result, a large delayed closure time of capillary aperture by platelet aggregates was recorded (Fig. 1; G. L. and R. F., unpublished data). Taken together, this evidence suggests that samples with instrumental flags for platelet clumps in EDTA-anticoagulated samples should be reanalyzed after blood collection by employing alternative anticoagulants, preferably those suitable for CBC. If platelet clumps are known or suspected, however, blood collection and CBC should be resolutely and immediately performed after collection of the blood with alternative anticoagulation by CPT.
REFERENCES 1 BOWEN KL, PROCOPIO N, WYSTEPEK E, GLAZIER J, MATTSON JC: Platelet clumps and leukocyte counts: A comparison between the Abbott CELLDYN 4000 and Coulter STKS. Lab Hematol 4:7, 1998 2 SOLANKI D, BLACKBURN B: Spurious leukocytosis and thrombocytopenia. JAMA 250:2514, 1983
3 LOMBARTS A, DE KIEVIET W: Recognition and prevention of pseudothrombocytopenia and concomitant pseudoleukocytosis. Am J Clin Pathol 89:816, 1983 4 SAVAGE R: Pseudoleukocytosis due to EDTA-induced platelet clumping. Am J Clin Pathol 81:317, 1984 5 LIPPI U, SCHINELLA M, MODENA N, NICOLI M, LIPPI G: Advantages of a new anticoagulant in routine hematology on the Counter S-Plus STKR analayzer. Am J Clin Pathol 93:760, 1990 6 LIPPI U, SCHINELLA M, NICOLI M, MODENA N, LIPPI G: EDTA-induced platelet aggregation can be avoided by a new anticoagulant also suitable for automated complete blood count. Haematologica 75:38, 1990 7 L IPPI G, G UIDI G, N ICOLI M: Platelet count in EDTA-dependent pseudothrombocytopenia. Eur J Haematol 56:112, 1996 8 PAPARO C, TAGINI E, MEDA R, SCOTT CS, NAVARO O: Improved stability of leukocytes in aged samples: Investigation of an alternative anticoagulant strategy in hematology for use with the Abbott CELL-DYN CD 3500 hematology analyzer. Eur J Lab Med 6:16, 1998 9 LAM SCT, HARFENIST EJ, PACHAM MA, MUSTARD JF: Investigation of possible mechanisms of pyridoxal-5-phosphate inhibition of platelet reactions. Thromb Res 20:645, 1980 10 HARRISON P, ROBINSON M, PASI J, SAVIDGE I, MACKIE I, MACHIN S: A reliable high shear test of platelet function: The PFA-100™. Lab Hematol 4:115, 1998
