Urine, uric acid Quantitative (24 hrs Urine Sample), Uricosuria

Sample

1. This test is done in the urine.
2. Collect urine for 24 hours.
   1. Discard the first sample (empty the urinary bladder), then collect all urine samples until 24 hours are completed.
   2. Also, add the last sample (empty the urinary bladder) to the container.
3. Do not refrigerate the urine; add NaOH (10 mL) to keep the urine alkaline.
   1. The urine will be stable at 22 °C to 24 °C for three days if there is no bacterial growth.

Indications

1. To find if kidney stones are due to high uric acid levels in the body.
2. Evaluates uric acid metabolism in gout.

It helps to evaluate the effect of uricosuric drugs.

Precautions

1. Some drugs increase the uric acid level like:
   1. Salicylates.
   2. Diuretics.
   3. Vitamin C.
   4. Cytotoxic drugs are used to treat cancers (leukemias and lymphomas).
   5. Strenuous exercise.
   6. Diet high in purines.
2. Allopurinol decreases the uric acid level.

Pathophysiology

1. Uric acid is the major product of catabolism of :
   1. Purine Nucleosides.
   2. Adenosine.
   3. Guanosine.
2. Nucleic acid precursors are purines, adenosine, and guanosine.
3. Dietary nucleic acid forms purines directly converted to uric acid.

4. Endogenous nucleic acid forms purines; these are excreted as uric acid into the urine.
5. Uric acid is readily filtered through the glomerulus.

6. Uric acid is absorbed + excreted by the kidney; only 6 to 12% of filtrate is uric acid in urine.
   1. The majority of the uric acid is excreted by the kidney and a small amount by the intestinal tract.
   2. Normally 1/3 of uric acid formed is degraded in the intestine by bacteria.
7. Excess of the uric acid is related to dietary intake of purines or endogenous uric acid production.
8. Uric acid exists in the more soluble form at a pH of > 5.75.
   1. Uric acid is undissociated at a pH of < 5.75.
9. Most uric acid is excreted in the urine, and the rest passes out in the stool.

7. Clinically hyperuricemia may lead to gout.
   1. This is also called gouty arthritis.
   2. It appears in large toe, feet, ankles, knee, and elbow are common sites.
   3. There is severe pain in the joints.
   4. There is the stiffness of the joints.
   5. There are limited movements of the joints.
   6. Joints are deformed.
   7. There are redness and swelling of the joints.
   8. There may be uric acid deposits called gouty tophi.
   9. There are more chances for the formation of uric renal stones.

Normal

Source 1

Diet	mg/day
The average on a normal diet	250 to 750 (1.48 to 4.43 mmol/day)
Purine free diet
Male	<420 0r (<2.48 mmol/day)
Female	Slightly lower
Low purine
Male	<480
Female	<480
High purine	<1000  ( <5.90 mmol/day)

Source 2

• Urine = 250 to 750 mg/24 hours   or
  • 1.48 to 4.43 mmol/24 hours

Another sources

• Men = 250 to 800 mg /24 hours
• Women = 250 to 750 mg /24 hours
• With purine free diet = <400 mg / 24 hours.
• With high purine diet = <1000 mg / 24 hours.

Raised urine uric acid level (Uricosuria) is seen in:

1. Gout.
2. Renal calculi.
3. Cancers (widespread disease).
4. Chronic myelogenous leukemia.
5. Multiple myelomas.
6. Viral hepatitis.
7. High – purine diet.
8. Wilson’s disease.
9. Sickle cell anemia.
10. Polycythemia vera.

Decreased urine uric acid level seen in:

1. Long-term alcohol abuse.
2. Chronic glomerulonephritis (chronic kidney disease).
3. Lead poisoning.
4. Xanthinuria.
5. Folic acid deficiency.
6. Cytotoxic drugs.
7. Eclampsia.
8. Acidosis (ketotic or lactic).
   

   Normal urine picture:

   Physical features	Chemical features	Microscopic findings
   Color = Pale yellow or amber Appearance = Clear to slightly hazy pH = 4.5 to 8.0 Specific gravity = 1.015 to 1.025	Blood = Negative Glucose = Negative Ketones= Negative Protein = Negative Bilirubin = Negative Urobilinogen = Negative (±) Leucocyte esterase = Negative Nitrite for bacteria = Negative	RBCs = Rare or Negative WBC = Rare or Negative Epithelial cells = Few Cast = Negative (Occasional hyaline) Crystal = Negative (Depends upon the pH of the urine) Bacteria = Negative

    

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