Urate Crystal Arthropathy (Gout)

Last updated: March 13, 2026

Gout is an acute-onset, crystal-induced arthritis that is characterised by intense joint pain and swelling – typically in the first metatarsal-phalangeal joint – when monosodium urate crystals are deposited.

Definition of terms

Term	Definition
Asymptomatic hyperuricaemia	Elevated serum urate level without signs and symptoms. It can progress to gout if it is not treated.
Acute polyarticular gout	Interstitial nephritis and chronic kidney disease are caused by the deposition of urate crystals in the renal tubules.
Tophaceous gout	Chronic gout is characterised by deposition of monosodium urate crystals in soft tissue, e.g., the pinna. Tophi cause deformity and disability if they are located near joints. They can also ulcerate.
Gouty nephropathy	Interstitial nephritis and chronic kidney disease are caused by the deposition of urate crystals in the renal tubules.

Crystals in gout vs pseudogout

	Gout	Pseudogout
Crystal type	Monosodium urate	Calcium pyrophosphate
Shape	Needle shaped	Rhomboidal
Birefringence	Negatively birefringent	Positively birefringent

Risk factors
- Reduced urate excretion
  - Advanced age
  - Male sex
  - Post-menopausal
  - Renal impairment
  - Hypertension
  - metabolic syndrome
  - Diuretics
  - Antihypertensives
  - Aspirin
- Excess urate production
  - Alcohol
  - Red meet
  - Sea food
  - Sweetners
  - Genetic disorders
  - Myeloproliferative disorders and lymphoproliferative disorders
  - Psoriasis
  - Tumor-lysis syndrome
  - Drugs, e.g., warfarin and cytotoxics
Precipitating factors
- Trauma
- Surgery
- Starvation
- Infection
- Diuretics
Associated conditions
- Cardiovascular disease
- Hypertension
- Diabetes mellitus
- Chronic renal failure
Pathophysiology
- Reduced excretion or increased production of urate → monosodium urate crystal formation → deposition of crystals in joints → acute inflammatory response
- Chronic inflammation → tophi, joint damage, and chronic pain
Signs and symptoms
- Acute monoarthritis
  - Acute onset
  - Severe pain, redness, swelling, and tenderness
  - May be polyarticular
  - Podagra commonly affects the first metatarsophalangeal joint
  - Other joints include the ankle, foot, small joints of the hand, wrist, elbow, and knee
Differentials
- Septic arthritis
- Reactive arthritis
- Haemarthrosis
- Calcium pyrophosphate deposition (CPPD)
Investigation
- Synovial fluid analysis
  - Monosodium urate crystals
  - WBCs > 2000/uL
- Serum urate: measured 4 – 6 weeks after an acute gout attack.
  - Elevated
  - It may be normal during an acute attack since crystals have been deposited in the joint(s)
- Plain radiograph
  - Soft-tissue swelling in the early stages
  - ‘Punched-out’ erosions in juxta-articular bone
  - Joint spaces are preserved in the early stages
- Ultrasound to visualize tophi
  - Hyperechoic structures
- Urea, electrolytes, and creatinine to properly dose allopurinol
- Complete blood count
  - WBC count may be raised
- Fasting glucose and lipid profile, since gout is associated with metabolic syndrome
Treatment
- Rest and elevate the joint
- Ice packs
- High-dose NSAIDS +/- PPI or colchicine (first-line)
  - Colchicine is slower to work
- Oral or intramuscular steroids if NSAIDs and colchicine are contraindicated
- Continue allopurinol during the acute attack if already established
Prevention
- Weight loss and exercise
- Avoid prolonged fasting
- Reduce alcohol intake
- Reduce consumption of purine-rich meats
- Low-dose aspirin
- Urate-lowering therapy
  - Allopurinol (first-line) – prescribed 3 weeks after an acute episode since it may trigger an attack.
  - Febuxostat (second-line)
  - Rasburicase in refractory cases
Indications for urate-lowering therapy
- 1 attack in 12 months
- Tophi
- Renal disease
- Uric acid nephrolithiasis
- As prophylaxis, if the patient is receiving cytotoxics or diuretics
Complications
- Tophi
- Degenerative arthritis
- Osteoporosis
- Nephrolithiasis
- Chronic pain and incapacitation

Reference Intervals ›

Biochemistry

ACTH	P: <80 ng/L
ALT	P: 5–35 U/L
Albumin	P: 35–50 g/L
Aldosterone	P: 100–500 pmol/L
Alk. phosphatase	P: 30–130 U/L
α-Amylase	P: 0–180 IU/dL
α-Fetoprotein	S: <10 kU/L
Angiotensin II	P: 5–35 pmol/L
ADH	P: 0.9–4.6 pmol/L
AST	P: 5–35 U/L
Bicarbonate	P: 24–30 mmol/L
Bilirubin	P: 3–17 μmol/L
BNP	P: <50 ng/L
CRP	P: <10 mg/L
Calcitonin	P: <0.1 mcg/L
Calcium (ionized)	P: 1.0–1.25 mmol/L
Calcium (total)	P: 2.12–2.60 mmol/L
Chloride	P: 95–105 mmol/L
Cholesterol	P: <5.0 mmol/L
VLDL	P: 0.128–0.645 mmol/L
LDL	P: <2.0 mmol/L
HDL	P: 0.9–1.93 mmol/L
Cortisol AM	P: 450–700 nmol/L
Cortisol Midnight	P: 80–280 nmol/L
CK ♂	P: 25–195 U/L
CK ♀	P: 25–170 U/L
Creatinine	P: 70–100 μmol/L
Ferritin	P: 12–200 mcg/L
Folate	S: 2.1 mcg/L
FSH	P: 2–8 U/L ♂; >25 menopause
GGT ♂	P: 11–51 U/L
GGT ♀	P: 7–33 U/L
Glucose (fasting)	P: 3.5–5.5 mmol/L
Growth hormone	P: <20 mu/L
HbA1C (DCCT)	B: 4–6%
HbA1C (IFCC)	B: 20–42 mmol/mol
Iron ♂	S: 14–31 μmol/L
Iron ♀	S: 11–30 μmol/L
Lactate (venous)	P: 0.6–2.4 mmol/L
Lactate (arterial)	P: 0.6–1.8 mmol/L
LDH	P: 70–250 U/L
LH	P: 3–16 U/L
Magnesium	P: 0.75–1.05 mmol/L
Osmolality	P: 278–305 mosmol/kg
PTH	P: 0.8–8.5 pmol/L
Potassium	P: 3.5–5.3 mmol/L
Prolactin ♂	P: <450 U/L
Prolactin ♀	P: <600 U/L
PSA	P: 0–4 mcg/mL
Protein (total)	P: 60–80 g/L
Red cell folate	B: 0.36–1.44 μmol/L
Renin (erect)	P: 2.8–4.5 pmol/mL/h
Renin (recumbent)	P: 1.1–2.7 pmol/mL/h
Sodium	P: 135–145 mmol/L
TBG	P: 7–17 mg/L
TSH	P: 0.5–4.2 mU/L
T4	P: 70–140 nmol/L
Free T4	P: 9–22 pmol/L
TIBC	S: 54–75 μmol/L
Triglycerides	P: 0.50–2.3 mmol/L
T3	P: 1.2–3.0 nmol/L
Troponin T	P: <0.1 mcg/L
Urate ♂	P: 210–480 μmol/L
Urate ♀	P: 150–390 μmol/L
Urea	P: 2.5–6.7 mmol/L
Vitamin B12	S: 0.13–0.68 nmol/L
Vitamin D	S: 50 nmol/L

Arterial Blood Gases

pH	7.35–7.45
PaCO₂	4.7–6.0 kPa
PaO₂	>10.6 kPa
Base excess	±2 mmol/L

Urine

Cortisol (free)	<280 nmol/24h
Hydroxyindole acetic acid	16–73 μmol/24h
Hydroxymethylmandelic acid	16–48 μmol/24h
Metanephrines	0.03–0.69 μmol/mmol cr.
Osmolality	350–1000 mosmol/kg
17-Oxogenic steroids ♂	28–30 μmol/24h
17-Oxogenic steroids ♀	21–66 μmol/24h
17-Oxosteroids ♂	17–76 μmol/24h
17-Oxosteroids ♀	14–59 μmol/24h
Phosphate (inorganic)	15–50 mmol/24h
Potassium	14–120 mmol/24h
Protein	<150 mg/24h
Protein/creatinine ratio	<3 mg/mmol
Sodium	100–250 mmol/24h

Haematology

WCC	4.0–11.0 ×10⁹/L
RBC ♂	4.5–6.5 ×10¹²/L
RBC ♀	3.9–5.6 ×10¹²/L
Hb ♂	130–180 g/L
Hb ♀	115–160 g/L
PCV ♂	0.4–0.54 L/L
PCV ♀	0.37–0.47 L/L
MCV	76–96 fL
MCH	27–32 pg
MCHC	300–360 g/L
RDW	11.6–14.6%
Neutrophils	2.0–7.5 ×10⁹/L (40–75%)
Lymphocytes	1.0–4.5 ×10⁹/L (20–45%)
Eosinophils	0.04–0.44 ×10⁹/L (1–6%)
Basophils	0–0.10 ×10⁹/L (0–1%)
Monocytes	0.2–0.8 ×10⁹/L (2–10%)
Platelets	150–400 ×10⁹/L
Reticulocytes	0.8–2.0% / 25–100 ×10⁹/L
Prothrombin time	10–14 s
APTT	35–45 s

Paediatric

Pulse Rate (bpm)
Neonate	140–160
Infant <1yr	120–140
1–5 years	110–130
5–12 years	80–120
>12 years	70–100
Respiratory Rate (tachypnoea)
0–2 months	≥60/min
2–12 months	≥50/min
1–5 years	≥40/min
>5 years	≥30/min
Blood Pressure (mmHg)
Term	65/45
1 year	75/50
4 years	85/60
8 years	95/65
10 years	100/70
Weight Formulas
3–12 months	(a + 9)/2 kg
1–6 years	2a + 8 kg
>6 years	(7a − 5)/2 kg
Haemoglobin (g/dL)
Term newborn	13–20
1 month	11–18
2 months	10–15
1–2 years	10–13
>2 years	11–14
MUAC (6 months–5 years)
Obese	>17.5 cm
Normal	13.5–17.4 cm
At risk	12.5–13.4 cm
Moderate malnutrition	11.5–12.4 cm
Severe malnutrition	<11.5 cm
Developmental Milestones
Social smile	1.5 months
Head control	4 months
Sits unsupported	7 months
Crawls	10 months
Stands unsupported	10–12 months
Walks	12–13 months
Talks	18 months
CSF WBC (/mm³)
Term newborn	0–25
>2 weeks	0–5

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