Evaluation of total leukocytes count by flow cytometry with Beckman Coulter® DXH900 in the presence of platelet aggregates.

The Beckman Coulter® DXH900 uses the impedance method to measure the total leukocytes count. In presence of platelet aggregates, the device identifies the structural changes and associates an alarm with the leukocytes result. The aim of this study was to evaluate the influence of platelet aggregates using the principle of flow cytometry as a second assessment of the white blood cell count. Total leukocytes count was evaluated in 49 specimens with presence of platelet aggregates and 32 without anomaly. The differences between total leukocyte count by the two automatic methods (impedance and flow cytometry) and the microscopic method were compared. Without platelet aggregates, the median values were 5.6 (microscopic cell count), 5.4 (impedance) and 5.4 (flow cytometry) and no discordance was observed. In presence of platelet aggregates, the median values were 5.6, 6.4 and 5.1 respectively. The graphical analysis with the allowable total error range of ± 25.7% showed substantial analytical discrepancies (15/49) using impedance method while the flow cytometry method revealed minor disagreements (3/49). Analytical discordances versus WBC reference ranges showed 88% agreement and a substantial Kappa coefficient of 0.70 by impedance, while the flow cytometry method had 94% agreement and a perfect Kappa coefficient of 0.83. The formation of platelet aggregates increased the total leukocyte count performed DXH900 impedance method. Our study has shown that DXH 900 flow cytometry method may be an alternative to exclude the presence of pseudoleukocytosis. In case flags are generated, the microscopic method may be needed for the confirmation of WBC count.

Study of haemolysis interference limit on serum potassium assay on Roche® Cobas 8000 and evaluation of corrected potassium.

Roche Diagnostics® decided a more restrictive haemolysis index (≤20 HI) for approval the release of serum potassium results. This study examined the risk of overestimating serum potassium results related to the HI according to the Ricos total error (±5.6%) and evaluated the approach of Martinez-Morillo and Alvarez to determine a corrected potassium. According to Ricos' criteria, our study showed compliant potassium results with HI less than or equal to 75. Between 90 and 100 HI, the results did not show a significant overestimation. The equation to obtain Kcorrected was: Kmeasured - (0.004 × HI). The use of corrective formulas for adjusting results of potassium could help the laboratory to identify patients at increased risk and to repeat the test as soon as possible.

Quality planning and control strategy for AQT90 flex Radiometer® in point of care testing.

In the context of point of care testing (PoCT) and ISO 22870, internal quality control (IQC) is a crucial part of PoCT accreditation processes. Quality Control materials shall be periodically examined with a frequency that is based on the robustness of the analytical procedure and the risk of harm to the patient from an erroneous result. We propose to apply the statistical quality control (SQC) procedure to develop an individualized QC plan for AQT90 flex instrument used in PoCT. The robustness is determined by the sigma-metric and analytical goal represented by an allowable total error (TEa) is evaluated using a Varela graphic tool. A Sigma-metric SQC run size nomogram for estimating the number of patient samples between IQC events. According to the calculated robustness we can distinguish 3 groups of parameters: HCG and CRP with large sample size per event, D-Dimer and Procalcitonin with an average sample size per event and Myoglobin. NT-proBNP. and Troponin T with a limited sample size per event. In PoCT, the SQC strategy can promote more effective, and not necessarily more frequent, IQC.