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Questions and Answers
What is the end product of purine metabolism in the liver?
What is the end product of purine metabolism in the liver?
Uric acid
Uric acid is present in RNA and DNA.
Uric acid is present in RNA and DNA.
True
A high turnover of nucleoproteins (purine, pyrimidine) occurs primarily in the brain and lungs.
A high turnover of nucleoproteins (purine, pyrimidine) occurs primarily in the brain and lungs.
False
In plasma, uric acid is present as what type of salt?
In plasma, uric acid is present as what type of salt?
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What is the approximate pool of uric acid in the body?
What is the approximate pool of uric acid in the body?
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About how much uric acid is formed daily in the body?
About how much uric acid is formed daily in the body?
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Which of the following are the primary locations where uric acid is excreted?
Which of the following are the primary locations where uric acid is excreted?
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Match the following compounds to their respective metabolic pathways:
Match the following compounds to their respective metabolic pathways:
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What is the process by which uric acid is filtered in the kidneys?
What is the process by which uric acid is filtered in the kidneys?
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Approximately what percentage of uric acid is reabsorbed in the proximal tubule of the kidney?
Approximately what percentage of uric acid is reabsorbed in the proximal tubule of the kidney?
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What is the primary mechanism by which uric acid is excreted from the body?
What is the primary mechanism by which uric acid is excreted from the body?
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The amount of uric acid excreted via the gastrointestinal tract is significantly greater than the amount excreted via the urine.
The amount of uric acid excreted via the gastrointestinal tract is significantly greater than the amount excreted via the urine.
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What type of sample can be used for a uric acid test?
What type of sample can be used for a uric acid test?
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How long is serum or plasma stable for at 4 degrees Celsius?
How long is serum or plasma stable for at 4 degrees Celsius?
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Which substances can cause positive interference with the uricase method used for uric acid testing?
Which substances can cause positive interference with the uricase method used for uric acid testing?
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A 24-hour urine sample for uric acid testing should be refrigerated.
A 24-hour urine sample for uric acid testing should be refrigerated.
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What is the recommended addition to a 24-hour urine sample to keep it alkaline?
What is the recommended addition to a 24-hour urine sample to keep it alkaline?
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Strenuous exercise has no significant impact on uric acid levels.
Strenuous exercise has no significant impact on uric acid levels.
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Which of the following conditions is a primary indication for a uric acid test?
Which of the following conditions is a primary indication for a uric acid test?
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A uric acid test can be helpful in assessing recurrent urinary stone formation.
A uric acid test can be helpful in assessing recurrent urinary stone formation.
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Uric acid testing is only recommended in adults and not in children.
Uric acid testing is only recommended in adults and not in children.
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What are the main reasons for an increased level of uric acid in the blood?
What are the main reasons for an increased level of uric acid in the blood?
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What is the normal range for uric acid concentration in serum?
What is the normal range for uric acid concentration in serum?
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Uric acid levels are always higher in females compared to males.
Uric acid levels are always higher in females compared to males.
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What factors primarily determine the blood level of uric acid?
What factors primarily determine the blood level of uric acid?
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Which of these conditions is NOT a cause of hyperuricemia?
Which of these conditions is NOT a cause of hyperuricemia?
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Which of these is NOT a cause of hypouricemia?
Which of these is NOT a cause of hypouricemia?
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Study Notes
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.
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Description
This quiz covers the essentials of uric acid, including its metabolism, formation, excretion, and clinical significance. Understand the role of uric acid in diagnosing conditions like gout and renal failure. Perfect for students studying biochemistry or clinical pathology.
