Uric Acid Test Overview

Uric Acid Test

• Uric acid is the end product of purine metabolism in the liver, containing adenine and guanine. It's also present in RNA and DNA. A high turnover occurs in the bone marrow and the gastrointestinal tract.
• In the blood, uric acid exists as monosodium salt. The total pool in the body is about 1200 mg, with approximately 600 mg formed and lost daily.
• GMP converts to guanosine, then to guanine, to xanthine, then to uric acid.
• AMP converts to adenosine, then to inosine, hypoxanthine, xanthine, and finally uric acid.
• Uric acid is excreted in the urine. About 75% is excreted in urine, 25% is destroyed by bacteria.
• Serum/plasma is stable for 3-5 days at 4°C. EDTA and fluoride interfere with the uricase method.
• Urine samples should be collected for 24 hours, not refrigerated, and made alkaline with NaOH.
• Severe exercise increases uric acid levels.
• Uric acid levels are used to diagnose gout, recurrent urinary stones, leukemia, and renal failure.
• Uric acid levels can also be used to monitor some cancer treatments, as rapid cell turnover can elevate uric acid levels.

Uric Acid Levels

• Normal serum uric acid levels are 3.5-7.2 mg/dL.
• Average values are slightly higher in males (by ~1 mg/dL) than in females.
• Blood uric acid levels depend on the synthesis rate in the liver and excretion rate by the kidneys.
• Excessive cell breakdown, nucleic acid catabolism and failure to excrete due to renal failure can increase uric acid levels.

Hyperuricemia (High Uric Acid)

• Causes include acute and chronic nephritis, urinary obstruction, high purine diet, diabetic ketoacidosis, malignant tumors, and certain genetic inborn errors (like Lesch-Nyhan syndrome, where hypoxanthine-guanine phosphoribosyl transferase is deficient).
• Von Gierke disease leads to acidosis because lactate competes with urate excretion.

Hypouricemia (Low Uric Acid)

• Causes include proximal renal damage, certain drugs (e.g., salicylates, allopurinol), Wilson disease, Fanconi syndrome, acromegaly, celiac disease, and xanthine oxidase deficiency.

Gout Diagnosis

• Physical Exam
• Medical History
• Blood test for uric acid
• Synovial fluid analysis (looks for needle-shaped crystals)
• Imaging tests
• Rule out other health conditions
• Increased uric acid levels in the blood (especially during attacks).
• Leukocytosis and increased ESR (an indication of inflammation).
• The presence of needle-shaped crystals in synovial fluid.

Crystals of Uric Acid

• Uric acid crystals precipitate in tissues below normal temperatures.
• Uric acid precipitation happens when its concentration in the blood exceeds 80 mg/dL. Tissues such as soft tissues in joints, urethra, and kidneys can all be affected.