Guide to blood tests in rheumatology
· Please perform both ESR and CRP if querying rheumatological conditions as discrepancy can be useful information.
· Beware CRP rises with increasing BMI
· ESR rises with age and anaemia
· Normal inflammatory markers can be seen in inflammatory arthritis. If clinical suspicion remains high despite normal blood tests then refer (this is especially true in psoriatic arthritis).
· ESR is more useful than CRP for diagnosing and monitoring PMR/Temporal arteritis.
· Can be positive in 5-20% normal population, especially at low titres (11-30).
· 70% of patients with RA will have positive RhF and 90% of patients with Sjorgens.
· RhF can be negative in Rheumatoid arthritis so if strong clinical suspicion still refer.
Anti-CCP ( Anticycylic citrullinated peptide)
· More specific for RA but can only be requested by secondary care
ANA ( Antinuclear antbodies)
· Only check if Autoimmune disease is suspected, ie. Symptoms include inflammatory arthritis, myalgias, rashes, mouth ulcers, recurrent serositis (pericarditis and pleurisy), and sicca symptoms (dry eyes and mouth).
· Prevalence of ANA in healthy people (3-30%), with higher levels in women and with increasing age.
· Even at high titres (>1:160), a positive ANA result alone does not indicate Autoimmune disease.
· Other conditions associated with positive ANA, include viral infections and cancers.
· Raised levels associated with gout
· Levels can be normal in gout especially at the time of acute attack
Arthritis Research UK- Approach to polyarthralgia ,2012; Gout 2016
American college of Rheumatology, Patient information-2015