Multiple Methods for Platelet Enumeration: Observation of a Newly Introduced Bias

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Abstract
After the introduction of Coulter S-Cal™, a bias became apparent between platelet counts obtained from instruments calibrated with this material and those obtained from a Clay Adams Ultra-Flo®. Statistical methods were used to compare platelet counts obtained from the Coulter S-Plus IV®, Ortho ELT-800®, Clay Adams Ultra-Flo 100®, and phase microscopy. At a P value of 0.01, paired t analysis revealed statistically significant biases between the Ultra-Flo and each of the other methods. Significant biases were also found between phase microscopy and each of the other methods, although these were of a smaller magnitude. The results indicate the necessity for users of multiple platelet counting methods to conduct comprehensive interinstrument evaluations, particularly when altering methods of calibration.