Skip to main content
Chemistry LibreTexts

3.2: Glucose in urine

  • Page ID
    120724
  • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

    RELATED READING: Chapter 32 SEE URINALYSIS INFOBASE.

    Glucose does not appear in the urine of healthy individuals. In diabetics, plasma glucose concentrations can be several-fold higher than that of healthy individuals. The kidney recovers glucose filtered through the glomerulus by active reabsorbtion by the cells of the proximal tubule. However, when the glucose concentration in the glomerular filtrate exceeds about 180 mg/dL, this reabsorptive capacity is exceeded. As a consequence, some of the filtered glucose is present in final urine. In general, the higher the plasma glucose, the greater the concentration in the final urine. However, urine output is a consequence of fluid intake, thus there is a considerable variance of glucose concentration (or many other analytes) in the urine of the same individual during a 24-hour period, or between individuals. The dipstick is a rapid method of determining the presence of urinary glucose, which can be used to screen for diabetes or monitor the therapy of diabetics.

    Principle of the Method

    The dipstick uses two coupled enzymatic reactions to measure the presence of glucose. The first reaction uses the enzyme glucose oxidase to oxidize the glucose, forming gluconic acid and hydrogen peroxide. The second reaction uses the hydrogen peroxide to oxidize a dye to form a colored product, or chromogen. The colored product can be visually observed or measured by an instrument. The amount of colored product formed is proportional to the amount of glucose present in the urine.

    The reactions are as follows:

    \[\text{Glucose} + O_{2} \rightarrow \text{Gluconic acid} + H_{2} O_{2}\]

    \[H_{2} O_{2} + \text{dye} \rightarrow \text{color change}\]

    The chromogen formation is visible after a minimal amount is converted. For many dipsticks this is in the range of 75-125 mg/dL of urine. There is also a maximum color change that can be obtained with the strip reagent. This is commonly set at 2000 mg/dL.

    Reagents

    All the reagents for the reaction are embedded in the pad of the dipstick. As with all reagents stored in a dried form, their stability is affected by moisture. Therefore the reagents must be protected from moisture. In addition, careful attention must be given to the manufacturer’s shelf life, which should appear on the label of every dipstick container.

    Specimen

    Freshly voided urine is the preferred specimen. The first urine specimen of the day is considered the most desirable, because it is the most concentrated. Urine specimens are acceptable up to four hours after voiding. Refrigerated specimens are acceptable up to 24 hours after excretion.

    Procedure

    Collect the urine in an appropriate specimen container. After verifying that the strips are working (see quality control) quickly dip the strip in the urine, removing excess liquid by moving the edge of the strip against the rim of the container as you remove the strip from the container. After this initial pass to remove excess liquid, remove any remaining liquid by touching the entire edge of the strip to a gauze pad or a paper towel. There should be no visible liquid on the strip except for that on the pad.

    Results

    Start timing the reaction as soon as the strip is placed in the urine. After 30 seconds read the strip visually. Match the observed color of the pad with the chart color on the bottle of strips or with a color chart, if that is available. Record your observation. If a Clinitek or other instrument is available, place the strip in the device as soon as you dip the strip and record the printed result. If reading visually, continue reading the results after 60 seconds, 120 seconds, and 300 seconds.

    Calculations

    No calculations are necessary for the visual readings. If instrument readings are made, the calibrated instrument calculates the urinary glucose concentration. If an instrument is used, correlate the visual reading with that of the instrument.

    Quality Control

    When visual readings are taken, be certain that the reader is not color blind. Before testing a test sample, take two strips and test a positive and a negative control sample. These results should be within accepted values. Ideally, a positive and negative control should be tested along with each batch of patient specimens tested.

    Expected values

    Urine from healthy individuals should give negative results. Urine from known diabetics may give positive results depending upon the extent to which their glucose is controlled and their fluid intake.

    STUDENT REPORT

    Solution Visual Color Score Instrument Value at Set Times
    Time 30 sec. 60 sec. 300 sec.
    QC negative
    QC positive
    1 g/L
    500 mg/L
    250 mg/L
    125 mg/L
    62 mg/L
    31 mg/L
    Test sugar solution 1
    Test sugar solution 2
    Test sugar solution 3

    Discussion Questions

    1. What is the range of linearity of the visual method?
    2. What is the range of linearity of the instrument?
    3. Does the test result change with time?
    4. If the result does change with time, Why?
    5. Does the range of linearity include all healthy and disease conditions?

    This page titled 3.2: Glucose in urine is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Lawrence Kaplan & Amadeo Pesce.

    • Was this article helpful?