Impact of Fasting on Complete Blood Count Assayed in Capillary Blood Samples

Background: To determine the effect of food intake on complete blood count (CBC) results. Method: We analyzed the CBC in whole capillary blood specimens collected from 33 adult volunteers into microtubes between 8: 00 AM and 11: 00 AM. Blood specimens were drawn from patients who had been fasting 12 hours and then 1 and 2 hours after consumption of a light meal containing carbohydrates, protein, and lipids. All measurements were performed using the hematologic analyzer Sysmex XN-1000. Results: The red blood cell count, hemoglobin concentration, hematocrit level, and platelet count decreased 2 hours after meal consumption (P =.007, P =.008, P =.003, and P =.03, respectively). The lymphocyte number decreased after the first and second hour following meal consumption (P =.004 and P =.001); the number of neutrophils had increased 1 and 2 hours after food intake (P =.003 and P =.006, respectively). Conclusions: Food consumption impacts CBC results. To ensure the consistency, quality, and repeatability of CBC analysis, blood should be drawn from fasting patients.