Which initial investigations should be considered for a patient presenting with new-onset joint pain?

Initial investigations for new-onset joint pain should be considered based on the suspected cause and the patient's overall condition, limiting them to those likely to significantly affect treatment decisions ¹.

• Urgent Considerations: If septic arthritis is suspected, the patient should be referred immediately according to the local care pathway ².
• Suspected Gout:
  • Measure the serum urate level to help confirm a clinical diagnosis of gout (a level of 360 micromol/litre or more) ². If the serum urate level is below this during a flare and gout is strongly suspected, repeat the measurement at least two weeks after the flare has settled ².
  • If the diagnosis of gout remains uncertain or unconfirmed, consider joint aspiration and microscopy of synovial fluid ².
  • If joint aspiration cannot be performed or the diagnosis remains uncertain, imaging with X-ray, ultrasound, or dual-energy CT may be considered ².
• Suspected Rheumatoid Arthritis (RA):
  • If suspected persistent synovitis is found on clinical examination, offer a blood test for rheumatoid factor ⁷.
  • If rheumatoid factor is negative, consider measuring anti-cyclic citrullinated peptide (CCP) antibodies ⁷.
  • X-ray the hands and feet ⁷.
  • It is important that these investigations do not delay referral for specialist opinion, especially if small joints of the hands or feet are affected, more than one joint is affected, or there has been a delay of three months or longer between symptom onset and seeking medical advice ⁷.
• Acute Childhood Limp:
  • If a child aged 3–9 years is well, afebrile, mobile but limping, and symptoms have been present for less than 72 hours (or are improving), and transient synovitis is suspected, no investigations are needed if symptoms are resolving ³,⁴,⁵.
  • If there is a history of trauma or focal bony tenderness on examination and no indications for referral, arrange a same-day X-ray ³,⁴,⁵.
  • If symptoms have not resolved completely, there is uncertainty about the diagnosis, or there is persistent limp with a normal initial X-ray, referral to paediatric orthopaedics or rheumatology may be needed for further investigations such as blood tests, X-ray, and ultrasound scan ³,⁴,⁵. Children outside the 3-9 age range or with red flag symptoms/signs require admission or referral for investigation ³,⁴,⁵.
• Suspected Bone or Joint Tuberculosis (TB): Investigations may include X-ray, CT, or MRI, along with biopsy or aspiration of joint fluid for culture ⁶.