Errors in Counting Platelets in Hemodialysis ...

The classical method for counting platelets (Thrombocytes) is use of two types of microscopy: Burcker Turk chambers (hemacytometer) and slides with peripheral blood smears. In the last ten years, a new method, flow cytometry with application of the impedance principle has been developed for CBC and counting of platelets. Scope: The current studies sought to compare the results of platelet counts from the optic microscope with the values obtained by use of flow cytometry and the impedance principle in samples obtained from patients before and after undergoing hemodialysis. Methods: Three methods were used to assess platelet counts of hemodialysis patients: optical microscopy, peripheral blood smear and use of the cytometry principle with impedance principale (VIC) by Coulter HNX hematological analysis. The study was performed on 90 patients, 55 men and 35 women, ages 35-65 years (mean age 50), hospitalized over a 3 month period. The patients were analyzed once monthly, all at the same day, before and after dialysis. The samples were assessed for platelet count by statistical parameters: [SD =(Xi- Xm)2 /n – 1; Acuracy: (%Diff = X average – X target/ X mean x 100, with normal value until + − 25) and Z score( Z = X average-Xtarget/SD, with normal value until +-2, R>0.95%), for average platelets 150-400 x10³/µl, 95% CI.]. Results: The comparison between the platelet counts on the Coulter HMX (mean value X‾ = 233 x 10³µl; p=0.028; SD=2; % Diff=0.90; Z score = - 0.30) and by optical microscopy (X‾ = 250 x 10³µl; p=0.029; SD= 2.6; %Diff = -3.6; Z score =0.40) yielded similar values in a control group (120 male and female healthy subjects, ages 25-55 years( mean age 40). A similarity between results for the methods was also found for the platelet counts of hemodialysis patients assessed using the Coulter HMX (Pre-dialysis, mean value X‾=230 x 10³µl; p=0.024; SD=3.45; % Diff = -4.53; Z score =2.5) and post-dialysis, (mean value X‾= 245 x 10³µl; p=0.034; SD=2.1; %Diff = 6.34; Z score = 0.10). However, differences were observed by use of optical microscopy in pre-dialysis, (mean value X‾=261 x 10³µl; p = 0.020; SD=7.1; %Diff= 5.90; Z score=3.90) and post-dialysis, (mean value X‾ 167 x 10³µl; p = 0.6; SD=4.2; %Diff= -7.10; Z score= -2.90).. The performance of the devices was assessed by Z score = < 1 = optic performance; 1 < Z < 2 = good performance; 2 < Z 3 = unsatisfactory performance. The platelet count determined on the peripheral blood smear was used to complement data from the quantitative methods and provided morphological information. Conclusion: The methods used to assess platelet counts of hemodialysis patients, optical microscopy, peripheral blood smear and use of the cytometry principle with impedance principale (VIC) have had appropriated results with samples from normal subjects but the accuracy of the automatic method ensures a high quality count of hemodialysis patients.