The authors of a new study are cautioning GPs not to use inflammatory marker to rule out underlying disease.
The research, published in the British Journal of General Practice, aimed to identify the value of inflammatory marker testing in primary care as a non-specific marker to rule out underlying disease.
The cohort study included 160,000 patients with inflammatory marker testing in 2014, and 40,000 untested age, sex and practice-matched controls. Data were drawn from the Clinical Practice Research Datalink. Patients who had received a diagnosis of cancer, autoimmune conditions or chronic infections in the two years before testing were excluded, as were patients with an acute infection in the 30 days before the index date.
The inflammatory markers considered were C-reactive protein (CRP), erythrocyte sedimentation rate (ESR) and plasma viscosity (PV).
The primary outcome was incidence of relevant disease (infections, autoimmune conditions and cancers) among those with raised versus normal inflammatory markers and untested controls. Process outcomes included rates of GP consultations, blood tests and referrals in the six months after testing.
The overall incidence of disease following a raised inflammatory marker was 15 per cent. The most common cause of raised inflammatory marker was infection (6.3%), followed by autoimmune conditions (5.6%) and cancers (3.7%).
Inflammatory markers had an overall sensitivity of less than 50 per cent for the primary outcome of any relevant disease.
For 1000 inflammatory marker tests performed, the authors estimated 236 false positives, resulting in an additional 710 GP appointments, 229 phlebotomy appointments and 24 referrals in the following six months.
The authors advised GPs that inflammatory markers have poor sensitivity and should not be used as a rule-out test, particularly given the frequency of false positives.