High incidence of significant urinary ascorbic acid concentrations in a west coast population--implications for routine urinalysis.
Examination of 4379 routine urinalysis specimens with dipsticks sensitive to ascorbic acid showed that 22.8% were positive specimens. The mean urinary vitamin C concentration in this population was 2120 mumol/L. There was a high rate of false-negative dipstick results for hemoglobin in patients with vitamin C in the urine. The highest false-negative rates were observed in urine samples containing less than 50 erythrocytes per high-power field. In further experiments when volunteers consumed supplemental oral USP vitamin C at doses of 100, 250, 500, and 1000 mg or vitamin C-containing fruit juices, even the lowest doses of oral vitamin C or juice resulted in sufficient urinary vitamin C to produce false-negative dipstick results in hemoglobin and glucose testing. To prevent potentially dangerous false-negative results, screening urinalysis protocols relying only on dipstick testing should include a check for urinary vitamin C or use a dipstick that is not subject to vitamin C interference.
Brigden
M L
ML
Island Medical Laboratories, Victoria, BC, Canada.
Edgell
D
D
McPherson
M
M
Leadbeater
A
A
Hoag
G
G
D001205:Ascorbic Acid / Q000008:administration & dosage / Q000652:urine*; D005188:False Negative Reactions; D006029:Glycosuria / Q000652:urine; D006456:Hemoglobinuria / Q000652:urine; D006801:Humans; D011934:Reagent Strips; D016482:Urinalysis / Q000592:standards*
D011934:Reagent Strips; D001205:Ascorbic Acid