Ascorbic acid (vitamin C) can appear in urine due to:
- Dietary Intake: High consumption of vitamin C-rich foods (e.g., citrus fruits, berries, peppers) or supplements can lead to excess ascorbic acid that the body doesn’t use, which is then excreted through the urine.
- Vitamin C Supplementation: Individuals taking vitamin C supplements, especially in high doses, may have ascorbic acid spill over into their urine because the body excretes the excess amount that it cannot absorb or store.
Since ascorbic acid is water-soluble, any surplus in the bloodstream is filtered by the kidneys and excreted in urine.
The detection of ascorbic acid (vitamin C) in urinalysis is significant because it can interfere with the accuracy of certain urine test results. Specifically, ascorbic acid can act as a reducing agent and cause false-negative results in the following tests:
- Glucose: Ascorbic acid can reduce the ability of urine dipsticks to detect glucose, leading to underestimation or a false negative in patients with glucosuria, like those with diabetes.
- Hemoglobin/blood: High levels of ascorbic acid can mask the presence of blood in the urine, which may lead to missed diagnoses of hematuria (blood in urine) from various causes, such as infections, trauma, or kidney issues.
- Bilirubin: Ascorbic acid can interfere with bilirubin detection, potentially leading to undetected liver dysfunction or bile duct blockages.
- Nitrite: It may cause a false-negative result in nitrite tests, which are used to screen for urinary tract infections (UTIs).
Thus, when high levels of ascorbic acid are detected, it’s important to be cautious about the reliability of these specific urine test results. Some modern urinalysis strips account for ascorbic acid interference by including a correction factor or additional tests to minimize this issue.
