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Laboratory Tests and Ancillaries
Specific investigations for confirmation of gouty arthritis include the following:
Synovial Fluid Analysis
Gout_Diagnostics 1
The demonstration of monosodium urate crystals in synovial fluid or tophus aspirates gives a definitive diagnosis of gout. Monosodium urate crystals are needle-shaped, and they exhibit strong birefringence under polarized light. It is recommended to search for monosodium urate crystals in all synovial fluid samples obtained from undiagnosed inflamed joints. Identification of monosodium urate crystals from asymptomatic joints may allow definite diagnosis in intercritical periods wherein patients are free of symptoms.
Serum Urate Levels
Gout_Diagnostics 2
Hyperuricemia is defined as a serum urate level >6.8 mg/dL (>0.40 mmol/L). The definition of hyperuricemia may vary between countries. Although hyperuricemia is the most important risk factor for gout, the presence of it alone is not diagnostic of gout. Many patients with hyperuricemia do not develop gout. During acute attacks, serum urate levels may be normal in about 10% of cases. It will be best to measure serum urate levels 2-3 weeks after an attack.
Additional Laboratory Exams to Detect the Presence of Associated Comorbidities in Patients with Gout
Upon detection of associated risk factors and comorbidities, the following should be addressed as an important part of the management of gout: Complete blood count to exclude infection, lymphoproliferative or myeloproliferative disorders; serum creatinine/urea to exclude renal disease leading to hyperuricemia or to detect renal disease secondary to urate nephropathy or nephrolithiasis; blood glucose to detect the presence of diabetes/insulin resistance; lipid profile to detect hypertriglyceridemia and low high-density lipoprotein (HDL) cholesterol; and a urinalysis showing the presence of blood and/or protein may suggest renal disorders.
Imaging
Plain Radiography/Skeletal X-ray
Gout_Diagnostics 3
The skeletal X-ray is usually normal in acute gouty arthritis, although there may be reversible soft tissue swelling around the involved joint. In chronic tophaceous gout, typical radiographic findings include erosions with sclerotic margins and overhanging edges of bones or calcification in some tophi. The presence of a thin, overhanging, calcified edge is highly suggestive of gout. The joint space is usually preserved until late stages of the disease.
Ultrasonography (US)
Gout_Diagnostics 4
Ultrasonography can detect crystals deposited on cartilaginous surfaces as well as tophaceous material and typical erosions. Monosodium urate crystals may appear as a “double contour sign” meaning there are deposits on superficial articular cartilage or as “snow storm appearance” denoting the presence within the synovial fluid of monosodium urate crystals.
Dual-Energy Computed Tomography (CT)
Dual-energy computed tomography allows the visualization of tophi or urate deposits in the articular and periarticular locations and can distinguish urate from calcium deposition.
Magnetic Resonance Imaging (MRI)
Magnetic resonance imaging findings are not specific for the diagnosis of gout but allow early detection of tophi and bone erosion. This is a method of determining the extent of disease in tophaceous gout and may provide information regarding the patterns of deposition and spread of monosodium urate crystals.