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Guide to blood tests in rheumatology

Inflammatory markers

·         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.

 

Rheumatoid Factor

·         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.

Uric acid

·         Raised levels associated with gout

·         Levels can be normal in gout especially at the time of acute attack

 

References

Arthritis Research UK- Approach to polyarthralgia ,2012; Gout 2016

American college of Rheumatology, Patient information-2015