Overview.
Joint pain (arthralgia) is one of the most common reasons for medical consultation. The critical clinical question is whether pain is inflammatory (autoimmune, crystal, infectious) or mechanical (osteoarthritis, injury). Blood tests transform this assessment — CRP and ESR detect systemic inflammation, uric acid identifies gout, rheumatoid factor and anti-CCP diagnose rheumatoid arthritis, and ANA screens for systemic autoimmune conditions. The right labs prevent years of misdiagnosis.
Inflammatory joint pain typically presents with morning stiffness lasting >30 minutes, joint swelling, warmth, and improvement with activity. Mechanical joint pain (osteoarthritis) is worse with activity, better with rest, and has brief morning stiffness (<15 minutes). This distinction drives the lab workup and treatment approach.
Prevalence: Joint pain affects ~30% of adults at any given time. Osteoarthritis is the most common cause overall. Rheumatoid arthritis affects ~1% of adults. Gout affects ~4% of adults (rising). Autoimmune arthritis is more common in women; gout is more common in men.
What to test.
First-line tests
- CRP — Distinguishes inflammatory from mechanical joint pain. Elevated CRP (>10 mg/L) with joint symptoms strongly suggests inflammatory arthritis, infection, or crystal disease. Normal CRP with joint pain supports osteoarthritis.
- ESR — Slower to change than CRP but captures chronic inflammation. Useful for monitoring disease activity in rheumatoid arthritis and polymyalgia rheumatica. Very high ESR (>100) suggests infection, malignancy, or giant cell arteritis.
- Uric Acid — Elevated uric acid (>6.8 mg/dL) is necessary for gout diagnosis but does not confirm a flare (levels can be normal during acute gout). Chronic hyperuricaemia is the underlying cause.
- CBC — Elevated white cells suggest infection or active inflammation. Anaemia of chronic disease accompanies many autoimmune arthritides. Thrombocytosis (elevated platelets) indicates active inflammation.
Second-line tests
- Rheumatoid Factor (RF) — Positive in 70-80% of rheumatoid arthritis. However, not specific — also positive in infections, other autoimmune diseases, and 5-10% of healthy elderly. Always order with anti-CCP for specificity.
- Anti-CCP (Anti-Cyclic Citrullinated Peptide) — Highly specific for rheumatoid arthritis (~95% specificity). RF-negative but anti-CCP-positive patients still have RA. Can be positive years before symptoms develop. More prognostically informative than RF.
- ANA (Antinuclear Antibody) — Screens for systemic autoimmune conditions: lupus (SLE), Sjögren's, systemic sclerosis. Positive in 95% of SLE. However, ANA is non-specific — positive in ~15% of healthy women. Only order if clinical features suggest systemic autoimmunity.
- Vitamin D — Vitamin D deficiency causes musculoskeletal pain that mimics inflammatory arthritis. It also worsens autoimmune disease activity. Cheap to test and treat.
Specialized tests
- HLA-B27 — Genetic marker present in 85-90% of ankylosing spondylitis and 50-70% of reactive arthritis. Consider in young adults with inflammatory back pain, sacroiliac tenderness, or enthesitis.
- Ferritin — Very high ferritin (>1000 ng/mL) with joint pain raises haemochromatosis suspicion — iron overload causing arthropathy. Check transferrin saturation if ferritin is markedly elevated.
Common causes.
- Osteoarthritis — Joint pain worse with activity, better with rest. Brief morning stiffness (<15 min). Affects weight-bearing joints (knees, hips) and hand DIP joints.
- Rheumatoid Arthritis — Symmetrical small joint swelling (MCP, PIP joints of hands; MTP joints of feet). Morning stiffness >30 minutes. Fatigue.
- Gout — Sudden severe pain, redness, swelling in a single joint — classically the big toe (podagra). Attacks last 7-10 days. Can affect ankles, knees, wrists.
Diagnostic patterns.
- Symmetrical small joint swelling + positive anti-CCP + elevated CRP — likely Rheumatoid arthritis. Next step: Rheumatology referral urgently; early DMARD therapy improves long-term outcomes
- Acute monoarthritis (big toe/ankle) + elevated uric acid + elevated CRP — likely Gout. Next step: Colchicine or NSAID for acute flare; discuss urate-lowering therapy if recurrent (allopurinol)
- Joint pain + positive ANA + rash + mouth ulcers + cytopenia — likely Systemic lupus erythematosus (SLE). Next step: Anti-dsDNA, complement levels (C3/C4), rheumatology referral
- Weight-bearing joint pain + normal inflammatory markers + age >50 — likely Osteoarthritis. Next step: X-ray confirmation; weight management, physiotherapy, analgesics
- Back pain + morning stiffness >30 min + HLA-B27 positive + young adult — likely Ankylosing spondylitis / axial spondyloarthritis. Next step: MRI sacroiliac joints; rheumatology referral
Lifestyle.
Non-medical causes
- Overuse or repetitive strain injury
- Post-exercise soreness (DOMS)
- Poor posture or ergonomics
- Deconditioning / sedentary lifestyle
- Weight-related mechanical stress on joints
- Previous injury (post-traumatic arthropathy)
Considerations
- Weight loss: every 1 kg lost reduces knee joint load by 4 kg
- Regular low-impact exercise (swimming, cycling, walking) strengthens supporting muscles
- Anti-inflammatory diet (Mediterranean pattern) may reduce inflammatory markers
- Vitamin D repletion if deficient
- Physical therapy for targeted joint strengthening
- Ergonomic workplace assessment for hand/wrist symptoms
FAQs.
What's the difference between inflammatory and mechanical joint pain?
Inflammatory: morning stiffness >30 minutes, swelling/warmth, improves with movement, elevated CRP/ESR. Mechanical: worse with activity, better with rest, brief morning stiffness (<15 min), normal blood markers. This distinction is the single most important clinical question — it determines the entire workup and treatment.
Should I get ANA testing for my joint pain?
Only if you have features suggesting systemic autoimmune disease — joint pain PLUS rash, mouth ulcers, hair loss, photosensitivity, kidney issues, or blood abnormalities. ANA is positive in ~15% of healthy women, so testing without clinical suspicion leads to unnecessary anxiety and further testing. It should not be a screening test for joint pain.
My uric acid is high but I've never had gout — should I treat it?
Asymptomatic hyperuricaemia (elevated uric acid without gout attacks) does not routinely require urate-lowering medication. However, it increases risk for future gout and is associated with cardiovascular and kidney disease. Lifestyle modification (reduce alcohol, purine-rich foods, fructose) is reasonable. Medication is typically started after the second gout attack or with complications.