Biochemistry: Determination of Uric Acid in Serum

Uric Acid

• Uric acid is produced by the breakdown of purines, which are nitrogen-containing compounds found in the body in substances such as nucleic acids (DNA, RNA).
• Uric acid formation occurs in the liver.

Foods High in Purines

• Red meat, liver, seafood (especially salmon, shrimp, and sardines)
• Food and drinks with high fructose corn syrup, spinach, mushrooms, green peas, beans, and wheat germ
• Alcohol

Excretion of Uric Acid

• Most uric acid is removed by the kidneys
• The remainder is excreted in the stools

Increased Uric Acid Levels

• Can accumulate in the body and cause gout
• Can lead to kidney disease, as a result of deposition in the kidneys or kidney stone formation
• Can be due to either increased production, decreased elimination, or a combination of both

Symptoms of Gout

• Arthritis that causes pain, swelling, and redness in the joints
• Fatigue
• Renal issues, including kidney stones, weight loss, joint heaviness or sensitivity

Uric Acid Test

• Helps diagnose and monitor treatment of gout
• Checks to see if kidney stones may be caused by high uric acid levels in the body
• Checks to see if medicine that increases or decreases uric acid levels is working
• Checks uric acid levels in people who are taking chemotherapy or radiation therapy

Assay Principle

• Determined by enzymatic, colorimetric method with uricase and 4-aminoantipyrine
• The intensity of the color produced is directly proportional to uric acid concentration
• Measured by increasing absorbance at 500-550 nm

Procedure

• Assay conditions: wavelength 500-550 nm, cuvette 1 cm light path, temperature 37°C or 15-25°C
• Sample: serum or plasma without any preparation, fasting for 4 hours is better
• Mix and incubate for 5 min at 37°C or 10 min at room temperature
• Read absorbance of samples and standard against the blank

Calculation

• Total Protein concentration: expected value is 3.4-7.0 mg/dl for males and 2.4-6.0 mg/dl for females

Hyperuricemia

• Causes: purine-rich diet, obesity or metabolic syndrome, hypothyroidism, certain medicines, excessive alcohol intake, genetics or familial, kidney disease, certain type of cancers

Treatment

• Manage symptoms of acute attacks
• Take one or more of the following medicine:
  • Nonsteroidal anti-inflammatory drugs (NSAIDs) such as ketoprofen
  • Colchicine prevents gout attacks
  • Corticosteroids
• Prevent recurrent attacks:
  • Uricosuric agents increase elimination of uric acid by the kidneys
  • Allopurinol decreases production of uric acid by the body