Uric acid’s maximum solubility in water is around 380 to 400 micromol/litre (6.4mg/dL to 6.8 mg/dL) but may be higher in serum, where it bonds to proteins, particularly albumin.[6,10]

Clinical testing reference ranges for serum uric acid levels for adults are typically between 150 - 430 micromol/litre for men and 140 - 360 micromol/litre for women in the UK. For gout diagnosis, NICE sets the serum urate level at 360 micromol/litre (6mg/dl) or more for either sex.[1]

Core symptoms and signs to suspect gout are:[1]

• rapid severe pain onset (typically overnight) with redness and swelling in one or both first metatarsophalangeal (MTP) joints at the base of the big toe, or in another joint (eg midfoot, ankle, knee, hand, wrist or elbow);
• the presence of tophi.

Other conditions to consider are:[1,13]

• septic arthritis (which requires immediate referral);
• inflammatory arthritis types;
• osteoarthritis;
• calcium pyrophosphate crystal deposits;
• bursitis;
• tenosynovitis;
• cellulitis;
• haemochromatosis (a long-term build-up of iron in the blood).

Septic arthritis should be considered in someone who is systemically unwell (whether or not with a raised temperature) with an acutely painful, hot, swollen joint.[13]

If a gout diagnosis is uncertain, it may be necessary to take a sample of the synovial fluid, or to use X-ray, ultrasound or a CT scan.[1]