BACKGROUND: Ascorbic acid, when present in biological samples, can produce a negative interference in several biochemical tests that use redox indicator systems. OBJECTIVES: We evaluated the ascorbic acid interference on serum biochemical tests in relation to the dose of vitamin C ingested and to the time of blood collection, and compared these results with in vitro interference. METHODS: Healthy volunteers (n =18) consumed increasing and successive doses of vitamin C (0.25 to 4g/day) for one week. Biochemical analytes were measured before and after each dose consumption. Serum samples were obtained 4, 12 and 24 h after vitamin C ingestion. Ascorbic acid was added in vitro to the human serum and the biochemical analytes were assayed up to 24 h after addition. RESULTS AND DISCUSSION: Serum ascorbic acid increased significantly after vitamin C ingestion, inhibiting the assays for urate and total bilirubin up to 24 h after ingestion (p < 0,01). In contrast, the ingested vitamin C did not interfere on the glucose, cholesterol, and triglycerides tests. In vitro ascorbic acid inhibited the reactions for all studied tests, proportional to the ascorbic acid amount and inversely proportional to the analyte concentrations. The urate test had in vitro interference only, whereas for bilirubin there were in vitro and, mainly, in vivo interference. CONCLUSION: To avoid false-negative results of serum urate and bilirubin we recommend the suspension of vitamin C intake at least 48 horas before blood collection.
Ascorbic acid; Laboratory interference; Serum analytes; Trinder's reaction
