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Introduction ⬇

Glucose is present in glomerular filtrate and is reabsorbed by the proximal convoluted tubule. If the blood glucose level exceeds the reabsorption capacity of the tubules, glucose will appear in the urine. Tubular reabsorption of glucose is by active transport in response to the body’s need to maintain an adequate concentration of glucose. The blood level at which tubular reabsorption stops is termed the renal threshold, which for glucose is between 160 and 180 mg/dL (9–10 mmol/L).

  1. Reduction tests

    1. These are based on reduction of cupric ions by glucose. When the compounds are added to urine, a heat reaction takes place. This results in precipitation and a change in the color of the urine if glucose is present.

    2. These tests are nonspecific for glucose because the reaction can also be caused by other reducing substances in the urine, including:

      1. Creatinine, uric acid, ascorbic acid

      2. Other sugars such as galactose, lactose, fructose, pentose, and maltose

    3. These tests have a lower sensitivity than enzyme tests.

  2. Enzyme tests

    1. These tests are based on interaction between glucose oxidase (an enzyme) and glucose. When dipped into urine, the enzyme-impregnated strip changes color according to the amount of glucose in the urine. The manufacturer’s color chart provides a basis for comparison of colors between the sample and the manufacturer’s control.

    2. These tests are specific for glucose only.

Normal Findings ⬆ ⬇

Random specimen: negative

24-hour specimen: ≤0.15 g/24 hr

Procedure ⬆ ⬇

  1. Use a freshly voided specimen.

  2. Follow directions on the test container exactly. Timing must be exact; the color reaction must be compared with the closest matching control color on the manufacturer’s color chart to ascertain accurate results.

  3. Record the results on the patient’s record.

  4. Refrigerate or ice the entire urine sample during collection if a 24-hour urine specimen is also ordered. See Table 3.3 for proper preservative.

Clinical Alert

  1. Urine glucose >1000 mg/dL (>55 mmol/L) (4+) is a critical value.

  2. Determine exactly what drugs the patient is taking and whether the metabolites of these drugs can affect the urine glucose results. Frequent updating in regard to the effects of drugs on blood glucose levels is necessary in light of the many new drugs introduced and prescribed.

  3. Test results may be reported as “plus” (+) or as percentages. Percentages are more accurate.

  4. When screening for galactose (galactosuria) in infants, the reduction test must be used. The enzyme test does not react with galactose.

  5. Newborns should always be tested by both methods (reduction and enzymatic).

Clinical Implications ⬆ ⬇

  1. Increased glucose occurs with:

    1. DM

    2. Endocrine disorders (thyrotoxicosis, Cushing syndrome, acromegaly)

    3. Liver and pancreatic disease

    4. Central nervous system disorders (brain injury, stroke)

    5. Impaired tubular reabsorption

      1. Fanconi syndrome

      2. Advanced renal tubular disease

    6. Pregnancy with possible latent diabetes (gestational diabetes)

  2. Increase of other sugars (react only with reduction tests, not dipstick tests)

    1. Lactose—pregnancy, lactation, lactose intolerance

    2. Galactose—hereditary galactosuria (severe enzyme deficiency in infants; must be treated promptly)

    3. Xylose—excessive ingestion of fruit

    4. Fructose—hereditary fructose intolerance, hepatic disorders

    5. Pentose—certain drug therapies and rare hereditary conditions

Clinical Alert

Urine glucose >1000 mg/dL (>55 mmol/L)test blood glucose, notify healthcare provider, and begin appropriate treatment

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain purpose of test, procedure for urine collection, the double-voiding technique, and interfering factors.

    1. For a random specimen: discard the first voided morning specimen and then void 30–45 minutes later for the test specimen. This second specimen reflects the immediate state of glucosuria more accurately because the first morning specimen consists of urine that has been present in the bladder for several hours.

    2. Advise the patient not to drink liquids between the first and second voiding so as not to dilute the glucose present in the specimen.

    3. A urine glucose test combined with a blood glucose test gives a more complete assessment of diabetes.

  2. Instruct the patient about the 24-hour urine collection procedure when applicable (see Long-Term, Timed Urine Specimen [2-Hour, 24-Hour]).

  3. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient regarding abnormal findings.

  2. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆

  1. Interfering factors for reduction test (false-positive results)

    1. Presence of non–sugar-reducing substances such as ascorbic acid, homogentisic acid, creatinine

    2. Tyrosine

    3. Nalidixic acid, cephalosporins, probenecid, and penicillin

    4. Large amounts of urine protein (slows reaction)

  2. Interfering factors for dipstick enzyme tests

    1. Ascorbic acid (in large amounts) may cause a false-negative result.

    2. Large amounts of ketones may cause a false-negative result.

    3. Peroxide or strong oxidizing agents may cause a false-positive result.

  3. Stress, excitement, myocardial infarction, testing after a heavy meal, and testing soon after the administration of intravenous glucose may all cause false-positive results, most frequently trace reactions.

  4. Contamination of the urine sample with bleach or hydrogen peroxide may invalidate results.

  5. False-negative results may occur if urine is left to sit at room temperature for an extended period, owing to the rapid glycolysis of glucose.

  6. High SG depresses color development; low SG intensifies it. see Appendix E for other drugs that affect test outcomes.