The platelet count in EDTA‐anticoagulated blood from patients with thrombocytopenia may be underestimated when measured in routine laboratories

Abstract

Spuriously low platelet counts (PCs) can be observed in normal blood samples anticoagulated with ethylenediamine tetra-acetic acid (EDTA) and, much less frequently, with citrate-tris-pyridossalphosphate (CPT), due to time-dependent in vitro platelet agglutination. Accuracy in PC determination is essential as PC is one of the parameters that usually guides treatment for thrombocytopenic patients. PCs of 93 thrombocytopenic patients were measured in EDTA-or CPT-anticoagulated blood samples immediately after sampling (t 0 ) and 90 min (t 90 ) after storage at room temperature. The presence of platelet agglutinates in blood samples was determined by examining blood smears using optical microscopy. PCs decreased at t 90 with both anticoagulants. Platelet agglutinates were present at t 90 in 27% of EDTA-samples vs. 2% of CPT-samples with decreased PCs (P < 0.001). Based on PCs in EDTA-samples, 15 patients (16%) shifted from a lower bleeding risk at t 0 to a higher bleeding risk category at t 90 (P 5 0.019), compared to 5 (5%) patients, based on PCs in CPT-samples. Therefore, time-dependent in vitro platelet agglutination in EDTA-blood samples may cause underestimation of PCs in thrombocytopenic patients, possibly leading to improper management.The accuracy of PC measurement is important for the diagnosis [1-5] and management [6][7][8][9][10][11] of patients with thrombocytopenia. Spuriously low PC is observed in 0.07-0.27% of blood samples [12][13][14] owing to the presence of antibodies that cause a time-dependent in vitro platelet agglutination. This harmless condition, termed ''pseudothrombocytopenia,'' is particularly common in blood samples collected in EDTA anticoagulant, which is used in routine laboratories for blood cell counts [12][13][14]. The use of other anticoagulants, such as citrate-tris-pyridoxalphosphate (CPT), prevents this phenomenon in some, albeit not all instances [15][16][17][18]. We hypothesized that the artifact responsible for pseudothrombocytopenia could contribute to spuriously decreased PCs also in patients with real thrombocytopenia. We assessed the effect of time elapsed since blood sampling and of the type of anticoagulant on PCs in patients with thrombocytopenia.The median PC in EDTA-anticoagulated blood samples was 58 3 10 9 /L (range, 2-143) immediately after blood sampling (t 0 ) and 55 3 10 9 /L (3-132) 90 min after storage at room temperature (t 90 ) (P 5 0.025). PC was lower in 49 patients (53%) and higher in 34 patients (38%) at t 90 , compared to t 0 (Table I). The frequency of patients with decreased PC was higher than that of patients with increased PC (p 5 0.04). At t 90 , platelet agglutinates in EDTA-blood smears were present in 27% of patients who exhibited a decrease in PC, and in one patient (3%) of those who exhibited an increase of PC (P 5 0.006) ( Table I). The median absolute decrease in PC in EDTAsamples displaying agglutinates at t 90 was 18 3 10 9 /L (10-71) vs. 3 3 10 9 /L (1-32) in those with no platelet agglutinates (P < 0.001). Based on PC in EDTA-samples at...

Learning the Ropes of Platelet Count Regulation: Inherited Thrombocytopenias

“…At the first identification of thrombocytopenia, "pseudothrombocytopenia", a relatively common artifactual phenomenon caused by platelet clumping in the test tube due to the presence of EDTA (ethylenediaminetetraacetic acid) as anticoagulant accounting for 0.07% to 0.27% of all cases of isolated thrombocytopenia, should be excluded [70].…”

In vitro variations of Mean platelet volume over time in blood samples collected in different anticoagulants from thrombocytopenic patients and healthy subjects

“…8,12,13 With the aim of reducing the pre-analytical variability associated with K3EDTAinduced platelet swelling, anticoagulants different from K3EDTA have been tested and proposed as potentially useful for assessing platelet indices. 9,14 To identify the ideal pre-analytical variables for measuring MPV, we compared its variation over time in blood samples collected in 4 different anticoagulants from the same normal subjects and patients with inherited or acquired thrombocytopenias. The mean platelet count (±SD) was 252 × 10 9 /L (±64) in blood donors and 75 × 10 9 /L (±35) in thrombocytopenic subjects.…”

Multi-anticoagulant and EDTA dependent pseudothrombocytopenia. Case reports on two pediatric patients

“…The microscopic examination can identify platelet clumping and repeated CBC tests, using a different anticoagulant, can clarify the diagnosis (8). When PLT aggregation occurs with EDTA, not only PLT counts are affected, but also WBC counts (in terms of increase) because most automated analyzers count cells by dimension, falsely recognizing the PLT clumps as being leukocytes (9-11).…”