Question
CASE \#1 A 52-year-old man submitted a urine specimen during his routine physical examination. QUESTIONS: 1. Which of the urinalysis test results are questionable and don’t balance with all three portions of the urinalysis? 2. What are three possible causes for the discrepant results? 3. What is the renal threshold for glucose? 4. Explain the discrepancy between the glucose oxidase method and the Clinitest. 5. List the sugars measured by each method and any interfering substances. 6. Describe a situation in which the results of the Clinitest would be positive, but the reagent strip test results would be negative. Presence of Glucose and Blood in the Urine Essay Paper
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Step 1/2
- The presence of glucose and blood in the urine, but the absence of significant ketones and elevated specific gravity, are questionable results that don’t balance with all three portions of the urinalysis.
- Three possible causes of the discrepant results are:
- Diabetes mellitus: Elevated blood glucose levels may exceed the renal threshold for glucose reabsorption, resulting in glucosuria. However, the absence of significant ketones and low specific gravity suggests that the patient may have well-controlled diabetes or another cause for glucose in the urine.
- Renal disease: Impaired renal function may lead to proteinuria, hematuria, and reduced urine concentrating ability, resulting in a low specific gravity. However, the presence of epithelial cells, casts, and bacteria in the urine also suggests an infection or inflammation of the urinary tract.
- Medications or diet: Some medications or foods may interfere with the urinalysis results, such as ascorbic acid (vitamin C), which can produce false-negative results for nitrites and leukocyte esterase, or acetylsalicylic acid (aspirin), which can cause transient proteinuria and hematuria.
Step 2/2
3. The renal threshold for glucose is typically 180 mg/dL or 10 mmol/L, which means that if the blood glucose concentration exceeds this level, glucose will spill into the urine and cause glucosuria. However, the renal threshold can vary depending on the patient’s age, renal function, and other factors.
4. The discrepancy between the glucose oxidase method and the Clinitest is due to the different principles of the two tests. The glucose oxidase method uses an enzyme to specifically react with glucose and produce a color change proportional to the glucose concentration. In contrast, the Clinitest uses copper ions to oxidize any reducing substances, such as glucose, fructose, galactose, and lactose, and produce a color change that is not specific to glucose. Therefore, the Clinitest may give false-positive results if other reducing substances are present in the urine, such as in patients with galactosemia or pentosuria.
5. The glucose oxidase method measures only glucose and is not affected by other reducing substances or ascorbic acid. The Clinitest measures all reducing substances, including glucose, fructose, galactose, and lactose, and can be affected by ascorbic acid or high doses of salicylates.
6. A situation in which the results of the Clinitest would be positive, but the reagent strip test results would be negative is if the patient has galactosemia, a rare genetic disorder that affects the metabolism of galactose. In galactosemia, galactose accumulates in the blood and urine, and may be detected by the Clinitest as a false-positive reducing substance. However, galactose does not interfere with the glucose oxidase method or the reagent strip test for glucose.
Final answer
- The presence of glucose and blood in the urine, but the absence of significant ketones and elevated specific gravity, are questionable results that don’t balance with all three portions of the urinalysis.
- Three possible causes of the discrepant results are:
- Diabetes mellitus: Elevated blood glucose levels may exceed the renal threshold for glucose reabsorption, resulting in glucosuria. However, the absence of significant ketones and low specific gravity suggests that the patient may have well-controlled diabetes or another cause for glucose in the urine.
- Renal disease: Impaired renal function may lead to proteinuria, hematuria, and reduced urine concentrating ability, resulting in a low specific gravity. However, the presence of epithelial cells, casts, and bacteria in the urine also suggests an infection or inflammation of the urinary tract.
- Medications or diet: Some medications or foods may interfere with the urinalysis results, such as ascorbic acid (vitamin C), which can produce false-negative results for nitrites and leukocyte esterase, or acetylsalicylic acid (aspirin), which can cause transient proteinuria and hematuria.
3. The renal threshold for glucose is typically 180 mg/dL or 10 mmol/L, which means that if the blood glucose concentration exceeds this level, glucose will spill into the urine and cause glucosuria. However, the renal threshold can vary depending on the patient’s age, renal function, and other factors.
4. The discrepancy between the glucose oxidase method and the Clinitest is due to the different principles of the two tests. The glucose oxidase method uses an enzyme to specifically react with glucose and produce a color change proportional to the glucose concentration. In contrast, the Clinitest uses copper ions to oxidize any reducing substances, such as glucose, fructose, galactose, and lactose, and produce a color change that is not specific to glucose. Therefore, the Clinitest may give false-positive results if other reducing substances are present in the urine, such as in patients with galactosemia or pentosuria.
5. The glucose oxidase method measures only glucose and is not affected by other reducing substances or ascorbic acid. The Clinitest measures all reducing substances, including glucose, fructose, galactose, and lactose, and can be affected by ascorbic acid or high doses of salicylates.
6. A situation in which the results of the Clinitest would be positive, but the reagent strip test results would be negative is if the patient has galactosemia, a rare genetic disorder that affects the metabolism of galactose. In galactosemia, galactose accumulates in the blood and urine, and may be detected by the Clinitest as a false-positive reducing substance. However, galactose does not interfere with the glucose oxidase method or the reagent strip test for glucose. Presence of Glucose and Blood in the Urine Essay Paper