Pseudothrombocytopenia: Manifestation of a New Type of Platelet Agglutinin

Abstract

Spuriously low electronic platelet counts were obtained on blood collected in EDTA from six patients. Platelet numbers on blood smears and electronic counts performed on blood collected in other anticoagulants were normal. Plasma or sera from these patients agglutinated homologous, as well as autologous platelets, in the presence of EDTA or DTPA, but agglutination did not occur in blood or platelet-rich plasma anticoagulated with heparin, oxalate, or citrate. Agglutination in the presence of EDTA was not inhibited by heparin, α-tocopherol, or N-ethylmaleimide, but was inhibitied by excess EDTA or divalent cation. The agglutinin was temperature independent in five of the six patients and had the physical and immunologic characteristics of a gamma globulin. The clinical significance and mechanism of EDTA-dependent agglutination of platelets is unknown.

Spurious counts and spurious results on haematology analysers: a review. Part I: platelets

“…Abnormal PLT from myeloproliferative diseases have been shown to be much more sensitive than normal ones to clumping in presence of EDTA (Norberg & Nilsson, 1987). Agglutinins were shown to be IgG, IgM, or IgA in 33-50%, 10-63%, and 4-40% of cases, respectively (Watkins & Shulman, 1970;Shreiner & Bell, 1973;Onder, Weisntein & Hoyer, 1980;Pegels et al, 1982;Imai et al, 1983;van Vliet, Kappers-Klunne & Abels, 1986;Casonato et al, 1994;Bizzaro & Brandalise, 1995;van der Meer et al, 2002). Agglutinins react more strongly at room temperature or below (« cold » agglutinins), but some are temperature independent or react even better at 37°C.…”

“…Ethylenediamine tetra-acetic acid (EDTA)-dependent pseudothrombocytopenia (EDP) is an in vitro phenomenon caused by specific proteins from the samples that react with PLT only in EDTA-anticoagulated blood and produce PLT clumps (Gowland et al, 1969;Watkins & Shulman, 1970;Shreiner & Bell, 1973;Berkman et al, 1991;Bizzaro & Brandalise, 1995) (Figure 1a). HA do not enumerate PLT from the large clumps and the number printed corresponds to that from a mixture of small clumps and unaggregated PLT, leading to PLT counts as low as 20 · 10 9 /l, whereas the accurate number is within normal ranges (Cohen et al, 2000).…”

“…HA do not enumerate PLT from the large clumps and the number printed corresponds to that from a mixture of small clumps and unaggregated PLT, leading to PLT counts as low as 20 · 10 9 /l, whereas the accurate number is within normal ranges (Cohen et al, 2000). Anticoagulants other than EDTA (citrate, oxalate and heparin) are also concerned in several reports (Watkins & Shulman, 1970;Shreiner & Bell, 1973;Onder, Weinstein & Hoyer, 1980;Pegels et al, 1982;Savage, 1984;Payne, 1985;Lombarts & de Kieviet, 1988;Cunningham & Brandt, 1992;Bizzaro, 1995). As thrombocytopenia discovered in a patient may induce several procedures including unnecessary bone marrow aspiration or/and PLT transfusion, recognition of this phenomenon is important (Payne & Pierre, 1984;Vicari, Banfi & Bonini, 1988;Foresti et al, 1990;Berkman et al, 1991;Bizzaro & Brandalise, 1995;Cohen et al, 2000).…”

“…But, in the latter instance, PLT aggregates may be generated in vivo and enumerated on HA if the relevant blood samples are anticoagulated with sodium citrate (Shimizu et al, 2003). The first important observation concerning the mechanism of aggregation in EDP was that serum or EDTA-plasma not only induced agglutination of PLT from the patient but also induced agglutination of EDTA-PLT from nearly all normal individuals (Watkins & Shulman, 1970;Shreiner & Bell, 1973;Veenhoven et al, 1979;Onder, Weinstein & Hoyer, 1980;van der Lelie, van der Plas-Van Dalen & von dem Borne, 1984), with the exception of PLT from patients with Glanzmann's disease, suggesting that the fibrinogen receptor, Glycoprotein (GP) alpha IIb beta IIIa (GPIIb/IIIa), was involved in EDP (Pegels et al, 1982;Casonato et al, 1994;Ryo et al, 1994;Bizzaro, 1995;Schrezenmeier et al, 1995). Indirect evidence is shown with artifactual pseudothrombocytopenia that develops frequently in patients following exposure to PLT GPIIb/IIIa receptor antagonists (Christopoulos & Machin, 1994;Stiegler et al, 2000).…”

Effect of prewarming EDTA blood samples to 37°C on platelet count measured by Sysmex XT‐2000iV in dogs, cats, and horses

“…Agglutination has been reported to be associated with the c globulin fraction and was inhibited by both anti-IgG and anti-IgM antisera. 3 Several studies have evaluated the use of various substances which decrease platelet clumping in feline blood such as prostaglandin E1 and CTAD (citrate, theophylline, adenosine, and dipyridamole). 4,5 Similar compounds have also been evaluated in human patients.…”