The diagnostic utility of inflammatory markers in primary care

: a mixed methods study

Abstract

Inflammatory markers are non-specific blood tests including C-reactive protein (CRP), erythrocyte sedimentation rate (ESR) and plasma viscosity (PV). These tests are commonly used by general practitioners (GPs) as an aid to the diagnosis and monitoring of inflammatory conditions including infections, autoimmune conditions, and cancers. Previous research into inflammatory markers has mostly been based in secondary care and explored relationships with single disease outcomes. This means it is less useful for GPs, who often use inflammatory markers in patients with undifferentiated symptoms who have multiple possible disease outcomes. There is also a lack of information about how GPs communicate the rationale for testing and the meaning of results with patients. My research addresses these evidence gaps.
Firstly, I conducted a series of quantitative studies using electronic health records of nearly 200,000 patients from the Clinical Practice Research Datalink (CPRD). The aim was to determine the epidemiology and diagnostic utility of inflammatory marker tests in primary care for relevant disease: defined as any infection, autoimmune disease or cancer. Secondly, I conducted a qualitative study, completing a total of 80 interviews with patients before and after receiving inflammatory marker results, and with the GPs who requested these tests. The aim was to explore the meaning of inflammatory markers for doctors and patients.
I have shown that, contrary to GPs perceptions, inflammatory markers are not a useful ‘rule-out’ test: in fact they miss around half of relevant disease in primary care. Testing more than one inflammatory marker simultaneously does not increase diagnostic accuracy. Although these tests are often used for reassurance, patients with ongoing symptoms perceived that normal results were unhelpful. I identified a lack of shared understanding and multiple barriers to shared decision-making. Results will be of interest to patients, GPs and commissioners wanting to optimise inflammatory marker testing in primary care.

Date of Award	28 Sep 2021
Original language	English
Awarding Institution	The University of Bristol
Supervisor	Jonathan P Banks (Supervisor), Penny F Whiting (Supervisor), William Hamilton (Supervisor) & Chris Salisbury (Supervisor)