Diabetes Mellitus:- Part 5 – Glucose in Urine (Glucosuria), Glycosuria, Benedict’s solution

Glucose in Urine (Glucosuria)

What sample of Glucose in Urine (Glucosuria) is needed?

1. The test sample is urine.
2. The best sample is after 2 to 3 hours of the meal.

What are the Indications for Glucose in Urine (Glucosuria)?

1. To diagnose diabetes mellitus.
2. To monitor diabetes mellitus.
3. To evaluate the effectiveness of the therapy.
4. To diagnose gestational diabetes.
5. It is part of a routine urine examination.

What are the precautions for Glucose in Urine (Glucosuria)?

1. Can see false-positive tests when any substance is present in the urine, which can reduce the copper in the clinitest strips.
2. It can detect false positive tests in the presence of other sugars, such as galactose, fructose, and lactose.
3. Drugs that can cause false positive tests include acetylsalicylic acid, Ascorbic acid, cephalothin, chloral hydrate, streptomycin, sulphonamides, and aminosalicylic acid.
4. Contamination from the oxidizing agents or bleach.
5. Improper storage of the urine strips.
6. Drugs giving false-negative results are levodopa, phenazopyridine, and ascorbic acid with clinitest strips.
7. Multistix detects ≥50 mg/dL; if the amount is less, it will be negative.
8. Sodium fluoride causes enzyme inhibition.
9. Refrigerated specimens give decreased enzyme activity.
10. Some drugs increase glucose in the urine, like diuretics (thiazides), estrogens, isoniazid, lithium, nalidixic acid, nicotinic acid, chloramphenicol, chloral hydrate, cephalosporin, and aminosalicylic acid.

How will you define Glucose in Urine (Glucosuria)?

• Glycosuria is the presence of reducing substances (glucose, galactose, lactose, and fructose) in the urine.
• Glucosuria is the presence of glucose in the urine. This is specific to the diagnosis of diabetes mellitus. Glucosuria may be associated with hyperglycemia and, in some cases, may occur without hyperglycemia.

How will you discuss the pathophysiology of Glucose in Urine (Glucosuria)?

1. Examination of urine for glucose is rapid, noninvasive, and inexpensive for screening urine.
   1. A large number of urine samples can be tested.
2. The glomeruli filter glucose, and all of the glucose is reabsorbed by the proximal convoluted tubules.
3. When glucose exceeds the renal threshold level (greater than 180 mg/dL) of the tubules, glucose appears in the urine, a condition known as glucosuria. https://labpedia.net/gestational-diabetes-mellitus-oral-gtt/.
4. Tubular absorption is an active process to maintain the body’s glucose level.
5. The renal threshold for glucose is 160 to 180 mg/dL.
   1. After the renal threshold values, glucose appears in the urine.
6. This test is neither sensitive nor specific for the control of diabetes because it does not detect glucose levels below 180 mg/dL.

What are the reducing substances in the urine?

1. Lactose.
2. Fructose.
3. Galactose.
4. Maltose.
5. Arabinose.
6. Xylose.
7. Ribose.

What Other reducing substances are found in the urine?

1. Uric acid.
   1. Creatinine.
   2. Cysteine.
2. Ketone bodies.
   1. Oxalic acid.
   2. Glucuronic acid.
   3. Hippuric acid.
   4. Homogentisic acid.
3. Drugs are:
   1. Ascorbic acid.
   2. Isoniazid.
   3. Salicylates.
   4. Formaldehyde.

What is the normal value of glucose in the urine?

Source 2

1. Normally, sugar (glucose ) is absent in the urine.
   1. Random specimen = Negative
2. 24-hours specimen = <0.5 g/day (<2.78 mmol/day).
3. Glucose appears in the urine when a blood glucose level of 180 mg/dL or more (crosses the renal threshold).
4. Its concentration in the urine correlates with the blood glucose level.

What are the Procedures for reducing substances in the urine?

Benedict’s solution method:

What is the principle of Benedict’s reaction?

1. It is a reaction that is a qualitative method and is very common.
2. It contains cupric ions complexed to citrate in an alkaline medium.
3. Reducing substances convert cupric to cuprous ions.
   1. It forms yellow cuprous hydroxide or red cuprous oxide.
4. This procedure will detect various sugars, including glucose.

1. CuSO4 (cupric sulphate) = 17.3 grams
2.  Sodium citrate (Na₃C₆H₅O₇-2H₂O) = 173 grams
3. Sodium carbonate (Na₂CO₃) = 100 grams
4. Distle water = 1000 mL

How will you prepare the Benedict solution?

1. Dissolve cupric sulfate in 100 mL of hot water.
2. Now, dissolve sodium citrate and sodium carbonate in 800 mL of hot water separately. Let it cool.
3. Mix solutions 1 and 2 and make up to 1000 ml of water.
4. Benedict’s reagent is ready and stable.

How will you perform the Benedict’s solution method?

1. This can also be done using Benedict’s solution.
2. Take 2.5 mL of Benedict’s solution (add 5 mL of Benedict’s solution).
3. Add 0.2 ml of urine (or 0.5 mL of urine or 10 drops of urine).
4. Place the tubes in a heat block (or a water bath) for 5 minutes, or heat them directly to 100 °C.
5. Allow to cool to room temperature.
6. Examine the color of each tube and the precipitate that forms.
7. Different colors develop according to the quantity of sugar in the urine.
8. Greenish-brown when there is a large quantity (>2 g/dL).

Another way to do Benedict’s reaction:

1. Benedict’s solution is 5 mL.
2. Urine  0.4 mL (8 drops).
3. Mix and keep in a boiling water bath for 5 minutes.

How will you perform the Benedict’s reaction using the tablet method?

1. Five drops of urine are mixed with 10 drops of water.
   1. Then add the tablet as known clinitest.
2. The procedure for Benedict’s reaction with the tablet (Clinitest) is shown in the following diagram.
   1. Also, run the negative control.

Reporting the result:

1. It can be reported as plus + signs, from 1+ to 4+.
2. It can report a percentage of 1% to 2 %. This reporting is more accurate.

What are the specific methods for glucosuria?

1. This method, which utilizes different strips such as Clinistix, Diastix, and Chemstrip, is available.
2. In all the above strips, the glucose-specific enzyme glucose oxidase is used.
3. This is more specific for glucose than Benedict’s method.
   1. This test is considered positive when the glucose concentration is 100 mg/dL or higher.

What is the sensitivity of the commercially available Discs?

1. Multistix = 75 to 125 mg/dL
2. Diastix  =  75 to 125 mg/dL
3. Chemstrip = 40 mg/dL in 90% of the specimen.

What are the drawbacks of the strips?

1. Urine strips primarily detect glucose, so there is a chance for false-negative results due to interfering chemicals in the urine.
2. False-positive results are seen in the following:
   1. If the detergents contaminate the container.
   2. In very dilute urine, traces may be seen due to sensitivity at low specific gravity.
   3. If the strips are exposed to air due to improper storage.
3. False-negative results are seen in the following:
   1. It is seen in the intake of vitamin C (ascorbic acid) and tetracyclines.
   2. In cases where there are high ketone bodies (≥40 mg/dL) and low glucose levels (75 to 125 mg/dL).
   3. Sodium fluoride inhibits the enzyme reaction; therefore, it should not be used in urine as a preservative.
   4. If urine is refrigerated, it may yield false-negative results due to decreased enzyme activity; therefore, bring the urine to room temperature.

Describe the quantitative method for Glucose in Urine (Glycosuria):

• This method uses hexokinase or glucose dehydrogenase procedures.

What are the causes of Increased glucose in urine?

1. Diabetes mellitus.
2. Renal glycosuria.
3. Hereditary defects in the metabolism of other reducing substances like galactose, pentose, and fructose.
4. Pregnancy.
5. Liver diseases.
6. Pancreatic diseases.
7. Thyrotoxicosis.
8. Cushing’s syndrome.
9. Acromegaly.
10. Brain injuries.
11. Shock.
12. Fanconi’s syndrome (Tubular defect).
13. Advanced renal tubular diseases.
14. Nephrotoxic chemicals like carbon monoxide, lead, and mercury.

What are the causes of false-negative results?

1. Mostly seen due to drugs.
   1. Ascorbic acid.
   2. Levodopa.
   3. Phenothiazine.

How will you compare Benedict’s reaction and the Oxidase method?

Questions and answers:

• Please see more details on Fasting Blood Glucose.