hyperuricemia

hyperuricemia
Name	Hyperuricemia
Synonyms	Uric acid excess
Field	Endocrinology, Nephrology, Rheumatology
Complications	Gout, Kidney stone disease, Uric acid nephropathy
Causes	Purine metabolism disorders, Chronic kidney disease, Lesch–Nyhan syndrome
Risks	Obesity, Hypertension, Metabolic syndrome
Diagnosis	Blood test, Uric acid
Treatment	Xanthine oxidase inhibitor, Uricase, Febuxostat
Medication	Allopurinol, Probenecid

hyperuricemia. Hyperuricemia is a biochemical condition characterized by an elevated level of uric acid in the blood. It is a key risk factor for the development of gout, a painful form of inflammatory arthritis, and is associated with various other metabolic and renal disorders. The condition arises from an imbalance between the production and excretion of uric acid, often influenced by genetic factors, diet, and comorbid diseases.

Definition and diagnosis

Diagnosis is primarily established through a blood test measuring serum uric acid concentration, with levels exceeding 6.8 mg/dL generally considered diagnostic. The American College of Rheumatology provides guidelines for interpretation, particularly in the context of gout. Differential diagnosis involves ruling out other causes of arthritis, such as septic arthritis or calcium pyrophosphate deposition disease. Laboratory assessment may also include a 24-hour urine collection to determine if the condition is due to overproduction or underexcretion of uric acid, a distinction critical for guiding therapy.

Causes and risk factors

Primary causes often involve inborn errors of purine metabolism, such as deficiencies in the enzyme hypoxanthine-guanine phosphoribosyltransferase seen in Lesch–Nyhan syndrome. Secondary causes are numerous and include increased cell turnover from conditions like myeloproliferative disorders or tumor lysis syndrome. Major risk factors encompass dietary habits high in fructose and purine-rich foods like organ meats, heavy alcohol consumption, particularly beer, and the use of medications such as diuretics and cyclosporine. Comorbidities like obesity, hypertension, type 2 diabetes, and chronic kidney disease are strongly associated, often as part of metabolic syndrome.

Pathophysiology

Uric acid is the end product of purine metabolism in humans, catalyzed by the enzyme xanthine oxidase. Hyperuricemia results from either overproduction, underexcretion by the kidneys, or a combination of both. Renal handling involves complex processes of glomerular filtration, reabsorption, and secretion primarily in the proximal tubule, influenced by transporters like URAT1. Solubility limits are critical; when serum levels exceed saturation, monosodium urate crystals can precipitate in joints, leading to gout, or in the renal interstitium, causing urate nephropathy. The inflammatory response to these crystals involves activation of the NLRP3 inflammasome and release of interleukin-1β.

Clinical manifestations

Many individuals are asymptomatic, identified only on routine testing. The most recognized clinical manifestation is acute gouty arthritis, typically affecting the first metatarsophalangeal joint. Chronic tophaceous gout can lead to joint destruction and visible tophi. Renal complications include kidney stone disease, specifically uric acid stones, and chronic urate nephropathy. An extreme manifestation is tumor lysis syndrome, which can cause acute uric acid nephropathy and acute kidney injury. Associations with cardiovascular disease, including hypertension and congestive heart failure, are also well-documented.

Management and treatment

Management strategies depend on the underlying cause and clinical presentation. First-line pharmacologic therapy for chronic management often involves xanthine oxidase inhibitors like allopurinol or febuxostat. For patients with underexcretion, uricosuric agents such as probenecid or lesinurad may be used. In severe or refractory cases, uricase enzymes like pegloticase are employed. Acute gout attacks are treated with nonsteroidal anti-inflammatory drugs, colchicine, or corticosteroids. Lifestyle modifications, including weight loss, reducing intake of high-fructose corn syrup and alcohol, and managing comorbidities like hypertension with losartan, are cornerstone recommendations.

Epidemiology

The prevalence of hyperuricemia varies globally, influenced by dietary patterns and genetic factors. High rates are reported in developed nations such as the United States and New Zealand, particularly among populations with high rates of obesity and metabolic syndrome. Incidence increases with age and is higher in males than in females, though rates in postmenopausal women approach those of men. Certain ethnic groups, including individuals of Pacific Islander and Māori descent, show a higher predisposition. The global burden is rising, paralleling trends in diabetes mellitus and chronic kidney disease.

Category:Metabolic disorders Category:Rheumatology Category:Nephrology