Unit Converter
Uric Acid
(End Product of Purine Metabolism - Key Marker for Gout, Kidney Function & Metabolic Syndrome)
Synonyms
- Serum urate
- UA
- Uric acid
- Monosodium urate (crystal form)
- Plasma urate
- Blood uric acid
Units of Measurement
- mmol/L
- µmol/L
- mg/dL
- mg/100 mL
- mg%
- mg/L
- µg/mL
Unit Conversions
Molecular Weight of Uric Acid = 168.11 g/mol
mmol/L ↔ mg/dL
1 mmol/L=16.8 mg/dL1\ \text{mmol/L} = 16.8\ \text{mg/dL}1 mmol/L=16.8 mg/dL 1 mg/dL=0.0595 mmol/L1\ \text{mg/dL} = 0.0595\ \text{mmol/L}1 mg/dL=0.0595 mmol/L
µmol/L ↔ mg/L
1 µmol/L=0.168 mg/L1\ \text{µmol/L} = 0.168\ \text{mg/L}1 µmol/L=0.168 mg/L 1 mg/L=5.95 µmol/L1\ \text{mg/L} = 5.95\ \text{µmol/L}1 mg/L=5.95 µmol/L
mg/100 mL = mg/dL = mg%
µg/mL ↔ mg/L
1 µg/mL=1 mg/L1\ \text{µg/mL} = 1\ \text{mg/L}1 µg/mL=1 mg/L
Description
Uric acid is the final oxidation product of purine metabolism in humans. Unlike most mammals, humans lack the enzyme uricase, which converts uric acid → allantoin.
Therefore, uric acid accumulates and circulates in blood as urate.
Excess uric acid leads to:
- Gout
- Kidney stones (uric acid nephrolithiasis)
- Cardiometabolic disease risk
- Renal dysfunction (urate nephropathy)
It is filtered, reabsorbed, secreted, and reabsorbed again in the proximal tubule, making its level sensitive to renal function.
Physiological Role
Even though considered a "waste" product, uric acid has roles:
- Potent antioxidant in plasma
- Helps scavenge free radicals
- Marker of purine turnover
- Influenced by diet, metabolism, and kidney handling
Clinical Significance
ELEVATED URIC ACID
Defined as:
- >7.0 mg/dL (0.42 mmol/L) in men
- >6.0 mg/dL (0.36 mmol/L) in women
Major Causes
1. Overproduction of Purines
- High purine diet: red meat, seafood, organ meats
- Alcohol (especially beer)
- Hematologic malignancies (tumor lysis)
- Psoriasis
- Myeloproliferative disorders
- Genetic enzyme defects (PRPP synthetase overactivity)
2. Underexcretion of Uric Acid
- Chronic kidney disease
- Dehydration
- Diuretics (thiazides, loop diuretics)
- Cyclosporine, tacrolimus
- Metabolic syndrome
- Lead nephropathy
- Hypertension
3. Mixed Mechanisms
- Tumor lysis syndrome
- Rhabdomyolysis
- Alcohol use
- Obesity
- Starvation, keto diets
Clinical Consequences
- Gout (monosodium urate crystal deposition)
- Tophi formation
- Uric acid kidney stones
- Acute urate nephropathy (especially in tumor lysis)
- Non-alcoholic fatty liver disease / insulin resistance
LOW URIC ACID
Less common; defined as <2.0 mg/dL (0.12 mmol/L).
Causes
- SIADH
- Severe liver disease
- Fanconi syndrome / proximal tubular dysfunction
- Wilson disease
- Xanthinuria (genetic uric acid deficiency)
- Malnutrition
- Very low purine intake
- Drugs: allopurinol, febuxostat, rasburicase, high-dose salicylates
Reference Intervals
(Tietz 8E + Mayo + ARUP + ACR Gout Guidelines)
Serum Uric Acid
- Men: 3.5 – 7.2 mg/dL (0.21 – 0.43 mmol/L)
- Women: 2.6 – 6.0 mg/dL (0.15 – 0.36 mmol/L)
Children
Lower values than adults.
Critical Values
- >13 mg/dL (0.77 mmol/L) in men
- >10 mg/dL (0.60 mmol/L) in women → high risk of renal complications.
Diagnostic Uses
1. Diagnosis & Monitoring of Gout
- Elevated urate with symptoms → gout
- Asymptomatic hyperuricemia does not always require treatment
2. Renal Function Assessment
Kidney excretion major determinant of uric acid levels.
3. Tumor Lysis Syndrome Monitoring
Rapid cell turnover → dangerous hyperuricemia.
4. Kidney Stone Risk Stratification
Uric acid lithogenicity increases with:
- Acidic urine
- High uric acid load
5. Metabolic Syndrome & CV Risk
High urate strongly associated with:
- Hypertension
- Obesity
- Insulin resistance
- NAFLD/MASLD
6. Pregnancy
Low uric acid → normal
High uric acid → risk of preeclampsia
Analytical Notes
- Enzymatic uricase-based assay is standard.
- Avoid hemolysis; purines released from RBCs may raise uric acid.
- Fasting sample preferred (diet strongly affects levels).
- Alcohol intake temporarily elevates urate.
Clinical Pearls
- Most hyperuricemia is due to underexcretion, not overproduction.
- A normal uric acid level does NOT exclude gout - 30% of acute gout attacks occur with normal urate.
- Uric acid rises earlier than creatinine in dehydration.
- Vitamin C and dairy intake help lower urate naturally.
- Uric acid stones dissolve in alkaline urine (pH > 6.0).
Interesting Fact
Humans lost the uricase gene during evolution, which may have helped survival by increasing antioxidant protection - but now predisposes modern populations to gout and metabolic disease.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Uric Acid
- American College of Rheumatology (ACR) Gout Guidelines
- KDIGO Kidney Disease Guidelines
- Mayo Clinic Laboratories - Uric Acid
- ARUP Consult - Metabolic / Renal Chemistry
- NIH / MedlinePlus - Uric Acid Test