No other substance excreted in the urine is known to give a positive result for glucose. False-positive results can be attributed to interfering substances in the environment where the strips are stored or used, such as hydrogen peroxide (H2O2) or bleach (hypochlorite).
False-negative results occur when elements present in the urine interfere with either the enzymatic reaction or prevent the oxidation of potassium iodide. Examples of some substances that may produce false-negative results, depending on the reagent strip that is used, include:
- large quantities of ketones
- ascorbic acid > 50 mg/dL
- 5-hydroxyindoleacetic acid
- homogentisic acid
- sodium fluoride ( a preservative)
A specific gravity higher than 1.020 may lower glucose reagent sensitivity, especially in the presence of a high (alkaline) urine pH. Exposing reagent strips to excess humidity may also reduce glucose reagent reactivity.
NOTE: Check the package insert of the reagent strips used in your laboratory for interfering substances that may affect glucose results.