DIURNAL CHANGE OF BLOOD-COUNT ANALYTES IN NORMAL SUBJECTS

Short-term, within one 24-hour day (diurnal period) within-person chan ges of the principal blood count analytes in healthy subjects were stu died at three major institutions. The results from each test site were indistinguishable and were therefore combined to make a database of 9 6 healthy subjects. Analytical imprecision of each analyte was subtrac ted from the total observed variation to give true diurnal change. Eac h analyte showed characteristic changes. As would be expected, cellula r properties of erythrocytes, such as MCV (mean cell volume) and MCH ( mean cell hemoglobin) showed negligible change. The red cell count, he matocrit, and hemoglobin showed changes that were consistent with flui d balance change. Total white cell count and some differential count c omponents showed major changes that raised questions of the confidence limits of clinical decision levels and the validity of commonly used reference intervals. Platelet count changes were typically less than a nalytic imprecision, suggesting the need for improvement in this aspec t of analyzer performance.