RESUMEN
OBJECTIVES: We studied the effect of a standardized breakfast or lunch before blood sampling on 77 analytes. DESIGN AND METHODS: The mean difference between assays from 20 healthy adults was calculated on blood samples taken before and after food intake. Significant differences were tested using two-tailed Student t-test and compared to the acceptable limits derived from analytical and intraindividual biological variation. RESULTS: Most of the analytes investigated were not significantly affected by food intake. Six of them were influenced by breakfast or lunch: triglycerides, glucose, creatinine, C-peptide and insulin were significantly upregulated, whereas testosterone was downregulated. Fourteen parameters were more influenced by time of sampling than by meals: nine decreased during the day (total bilirubin, BNP, myoglobin, cortisol, TSH, C-telopeptide, prolactin, ACTH, uric acid) and two increased (white blood cells, neutrophils). Three parameters showed levels that were similar at 9:00 am and 5:00 pm but their lowest level at 12:30 pm (inorganic phosphorus, osteocalcin, PTH). CONCLUSIONS: Fasting is necessary for some laboratory tests. Clinicians should be aware of variations due to sampling time before ordering non-fasting tests, and in the subsequent interpretation of results.