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Introduction ⬇

Some types of tablet, tape, and dipstick tests are available for UA outside the laboratory setting. They can be used and read directly by patients and healthcare providers.

Similar in appearance to pieces of blotter paper on a plastic strip, dipsticks actually function as miniature laboratories. Chemically impregnated reagent strips provide quick determinations of pH, protein, glucose, ketones (acetone or acetoacetic acid), bilirubin, hemoglobin (blood), nitrite, leukocyte esterase, urobilinogen, and specific gravity (SG). The dipstick is impregnated with chemicals that react with specific substances in the urine to produce color-coded visual results. The depth of color produced relates to the concentration of the substance in the urine. Color controls provided with the dipstick are compared against the actual color produced by the urine sample. The reaction times of the impregnated chemicals are standardized for each category of dipstick; it is vital that color changes be matched to the control chart at the correct elapsed time after each stick is dipped into the urine specimen. Instructions that accompany each type of dipstick outline the procedure. When more than one type of test is incorporated on a single stick (e.g., pH, protein, and glucose), the chemical reagents for each test are separated by a water-impermeable barrier made of plastic so that results do not become altered (Table 3.1). In addition to dipsticks, reagent strips, tablets, and treated slides for special determinations such as bacteria, phenylketonuria (PKU), mucopolysaccharides, salicylate, and cystinuria are available for UA.

Procedure ⬆ ⬇

  1. Use a fresh urine sample within 1 hour of collection or a sample that has been refrigerated; if refrigerated, bring to room temperature and mix specimen.

  2. Read or review directions for use of the reagent. Confirm the reagent is not expired. Periodically check for changes in procedure.

  3. Dip a reagent strip into well-mixed urine and then remove it, blot, and compare each reagent area on the dipstick with the corresponding color control chart within the established time frame. Correlate color comparisons as closely as possible using good lighting.

Interfering Factors ⬆

  1. If the dipstick is kept in the urine sample too long, the impregnated chemicals in the strip might be dissolved and could produce inaccurate readings and values.

  2. If the reagent chemicals on the impregnated pad become mixed, the readings will be inaccurate. To avoid this, blot off excess urine after withdrawing the dipstick from the sample.

Clinical Alert

  1. Precise timing is essential. If the test is not timed correctly, color changes may produce invalid or false results.

  2. When not in use, the container of dipsticks should be kept tightly closed and stored in a cool, dry environment. If the reagents absorb moisture from the air before they are used, they will not produce accurate results. A desiccant comes with the reagents and should be kept in the container.

  3. Quality control protocols must be followed:

    1. The expiration date must be honored even if there is no detectable deterioration of strips.

    2. Bottles must be discarded 6 months after opening, regardless of expiration date.

    3. Known positive and negative (abnormal and normal) controls must be run for each new bottle of reagent strips when it is opened and whenever there is a question of deterioration.