Proficiency Testing of Platelet Counting in Ontario

Abstract

Proficiency testing results provide data for interlaboratory comparisons. The Laboratory Proficiency Testing Program of Ontario, Canada, has tested platelet counting for a decade and other hematology parameters for 15 years. Despite the fact that all testing programs are compromised by the type of testing material used, for platelet count testing, conclusions are possible. The data indicate that most laboratories in Ontario have greater difficulty performing reproducible platelet counting as compared with other components of hematologic cytometry. A major contributor to this shortfall is the method used by the laboratory. It was not a surprise that manual counting had a high coefficient of variation. Unexpectedly, the semiautomated methods used in the mid-1980s also displayed a high coefficient of variation.

Evaluation of low platelet counts by optical, impedance, and CD61‐immunoplatelet methods: estimation of possible inappropriate platelet transfusion

“…12 Of the available methods for determining the PLT count, the IMP principle is still the most commonly used, even though it is unable to provide consistently accurate PLT counts in the lower thrombocytopenic range (<20 ¥ 10 9 /L). 1,13,14 This is because of a progressive loss of linearity, an increasing influence of background noise and sample debris below 20 ¥ 10 9 /L, and a decreasing statistical confidence owing to the few events actually counted. 15 The accuracy and reliability of IMP PLT counts are also affected by sample interference such as red blood cell or white blood cell fragments, which typically lead to overestimates of the true PLT count.…”

Evaluation of the platelet counting by Abbott CELL‐DYN® SAPPHIRE™ haematology analyser compared with flow cytometry

“…Impedance platelet counts are essentially derived from particle counts within defined ranges and take no account of other structural or morphological changes; in contrast, optical methods, which show wider instrument-specific variations in terms of scatter angle measurements, are likely to be affected by both morphological and volume changes. Several limitations of conventional counting methods in general and impedance methods in particular, are recognised (Lohmann, Crawford & Wood, 1992;Dickerhoff & Von Ruecker, 1995;Koh, Kabutomori & Hishiyama, 1996;Harrison et al, 2000) and the potential sample interference that can potentially compromise the accuracy of a platelet count is considerably high. Commonly this interference results from the presence of sample particles with a similar size or optical characteristics to platelets that cannot be sufficiently discriminated from platelets.…”

Automated CD61 immunoplatelet analysis of thrombocytopenic samples

“…Among the most important factors that mitigate against implementation of a reduced trigger point for platelet transfusion are the recognized limitations of conventional counting methods in general and impedance methods in particular (Lohmann et al , 1992; Dickerhoff & von Ruecker, 1995; Koh et al , 1996; Harrison et al , 2000). The confidence and reliability of impedance platelet counts progressively diminish below a count of 20 × 10 9 /l, and the frequency of potential sample interferences that can potentially compromise the accuracy of a platelet count is considerably higher in patient populations with thrombocytopenia.…”

“…Current platelet transfusion practice is inherently based on an assumption that platelet counts reported by haematology analysers have some degree of accuracy, although there are a number of reasons why this may not always be true in the context of thrombocytopenia. Of the available methods for determining the platelet count, the impedance principle is still the most commonly used, even though it is unable to provide consistently accurate platelet counts in the lower thrombocytopenic range (< 20 × 10 9 /l) (Lohmann et al , 1992; Dickerhoff & von Ruecker, 1995; Koh et al , 1996). This is because of a progressive loss of linearity, an increasing influence of background noise and sample debris below 20 × 10 9 /l, and a decreasing statistical confidence owing to the few events actually counted.…”