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The page below is a sample from the LabCE course Chemical Screening of Urine by Reagent Strip. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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False-Positive and False-Negative Urine Glucose Results

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
  • aspirin
  • ascorbic acid > 50 mg/dL
  • levadopa
  • 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.