Estimation of the Lower Limits of Manual and Automated Platelet Counting

Abstract

Most evaluators of automated or manual methods for platelet counting focus on characteristics such as imprecision, linearity, and carry over. The limits of the analytical procedure are usually not assessed. The limits of the different techniques are neither discussed in the literature nor do manufacturers of analytical systems supply these data.A new procedure is presented to assess the performance of the manual as well as the automated platelet count. This procedure allows, with defined statistical confidence (eg, 95%), the determination of (1) the limit of platelet detection (LD) at which signals of platelets can be discriminated from the system noise; (2) the lower limit of quantification (LLQ), at which a certain imprecision is not surpassed; and (3) the The determination of the number of leukocytes, erythrocytes, and platelets in blood is of great importance in many diagnostic processes. Two analytical procedures are commonly used for blood cell counting: the manual and the automated count. Manual methods for cell counting are known to be time consuming and tedious. 1It is common knowledge that manual cell counting is burdened with high imprecision.2 Nevertheless, these techniques are still used as routine methods in the laboratories of many practitioners or if low or high cell count ranges or atypical cells are present also in specialized hematology laboratories.The introduction of electronic cell counters permit a more precise enumeration of erythrocytes, leukocytes, and platelets and has reduced these drawbacks significantly. Coefficients of variation (CV) <3% can be obtained. 3 The precision and accuracy of electronic cell counters is better compared to manual counting mainly because a much higher number of cells is counted.2 This fact might lead to the assumption that this superior performance can be observed over the entire measuring range. Few authors have stressed the fact that this assumption is valid only for a limited measuring interval. 4 In the past, neither the LD nor the LLQ have been determined. When describing the analytical performance of an instrument, manufacturers of cell counters and evaluators of new instruments pay much attention to international committee recommendations.5 These include issues such as linearity, imprecision, and carry over, 67 but only a few authors ask what the limits of cell counting are at various platelet count levels. 6,8 At low platelet numbers, because fewer cells are counted, observed CVs are expected to be increased and even the use of automated cell counters may be inappropriate.5 For very high cell numbers, it is mainly the inaccuracy of the cell count that has to be critically evaluated. It is common practice to use manual counting methods if platelet numbers are low. The decision to use manual rather than electronic counting is based more on subjective impressions than on a solid statistical basis. In 1986, Hackney and coworkers 9 pointed out that there is a need for improvement in instrument and kit evaluations and stated that in contrast to clinical c...

Initial performance evaluation of the UniCel® DxH 800 Coulter® cellular analysis system

“…Generation of the flag requires verification by another method (either manual chamber count or FCM), with the manual chamber count carrying a high coefficient of variation and FCM being impractical or unavailable for many laboratories. (Hanseler, Fehr & Keller, 1996; Harrison et al , 2000). The DxH 800 boasts a significant increase in the amount of information (256 channels) collected on each sample.…”

Platelet Transfusion Therapy

“…In addition, although contemporary blood cell counters are quite accurate at low platelet counts, small variations in count can result from limitations of the technology, and the decision to transfuse should therefore be based on the clinical situation and the pattern of recent platelet counts as well as the absolute platelet count at a given moment. 50 …”

Is automated platelet counting still a problem in thrombocytopenic blood?

“…Hanseler et al 11 using the H1 counter, claimed that for counts of less than 30,000 platelets per µL, the automated counting should be replaced by the manual chamber procedure. Our data obtained with thrombocytopenic patients also suggest the same for the onedimensional STKS, H1 and T-890 counters.…”

“…[1][2][3][4][5] However, automated counting is still very controversial in the case of samples from thrombocytopenic or other patients in which other small particles could generate electrical or optical signals that are similar to platelets, such as debris and red cell fragments. 4,[6][7][8][9][10][11] Most counters nowadays employ the principle of electrical impedance or optical signals for counting the platelets in peripheral blood, using the particle volume for counting them. 12 On the other hand, the presence of large platelets beyond the upper threshold may lead to underestimation of the platelet counts.…”