Monosodiumurat

Monosodium urate is the sodium salt of uric acid and the principal form in which urate occurs in human fluids. It consists of the urate anion (C5H3N4O3−) associated with a sodium counterion and can crystallize as hydrates in biological systems. Uric acid is the end product of purine metabolism in humans, and serum urate is normally regulated by renal excretion. When production exceeds excretion, serum urate can rise above its solubility limit (about 6.8 mg/dL at body temperature), leading to precipitation of monosodium urate crystals in joints and soft tissues.

Clinical significance arises mainly in gout. Monosodium urate crystals are needle-shaped and, under polarized light, are strongly negatively birefringent, appearing yellow when aligned parallel to the slow axis and blue when perpendicular. Crystals trigger acute inflammatory arthritis and can form tophi in chronic disease. They may also contribute to uric acid nephrolithiasis.

Diagnosis is typically by identifying MSU crystals in synovial fluid or tophus sent for polarized light microscopy. Differentiation from other crystal arthropathies, such as calcium pyrophosphate deposition disease, relies on crystal morphology and birefringence.

Management aims to control flares and reduce urate levels. Acute gout is treated with NSAIDs, colchicine, or corticosteroids. Long-term management uses urate-lowering therapy (for example, allopurinol or febuxostat) or uricosuric agents in suitable patients, with the goal of maintaining serum urate below the crystallization threshold to prevent new crystal formation and promote dissolution of existing deposits.