Ascorbic acid interference in the measurement of serum biochemical parameters: in vivo and in vitro studies.

OBJECTIVES

To investigate the negative interference of ascorbic acid in serum biochemical tests in relation to the dose of vitamin C intake and to the time of blood collection.

DESIGN AND METHODS

Healthy volunteers (n = 18) consumed daily doses of vitamin C (0.25-4.0 g) for 1 week and serum parameters were assayed prior to the experiment and on the eighth day of consumption. Blood samples were collected 4, 12 and 24 h after vitamin C intake.

RESULTS

Serum levels of ascorbic acid increased significantly after vitamin C ingestion inhibiting urate and total bilirubin tests 4 and 12 h after intake (P < 0.01). A significant negative interference occurred up to 24 h after consumption of 4 g vitamin C for the urate test. In contrast, ingestion of vitamin C did not show interference in glucose, triglyceride and cholesterol tests. Addition of ascorbic acid to serum inhibited the urate test to a similar extent to that observed after vitamin C intake. However, after ingesting vitamin C, the interference for the bilirubin test was greater than that of the in vitro interference.

CONCLUSIONS

Commonly taken doses of supplementary vitamin C interfered negatively with the serum urate test based on the Trinder method, and with bilirubin metabolism.