‘I’m fishing really’. Inflammatory marker testing in primary care: a qualitative study.

Problem

Millions of inflammatory marker tests (CRP, plasma viscosity and ESR) are performed in the UK annually and rates of testing are rising. It is not known whether it is appropriate to order so many inflammatory markers and what should be done with abnormal results. Most research into inflammatory markers looks at diagnosis of specific diseases and comes from secondary care and qualitative studies are lacking. We aimed to explore the real life complexity of test ordering through qualitative interviews with GPs and nurse practitioners.

Approach

We undertook qualitative interviews with twenty-six GPs and nurse practitioners. Clinicians reviewed recent cases of inflammatory marker testing in their pathology inbox, with a topic guide used to provide prompts. Interviews were audio-recorded and transcribed. Analysis was conducted by two researchers using a grounded theory approach.

Findings

Clinicians use inflammatory markers as part of the diagnostic workup for specific diseases or for monitoring disease activity. A third use is as a screening/triage tool to differentiate between the presence or absence of disease.

"I'm fishing really. So it's, a lot of our work is early presentation of undifferentiated disease and I get, essentially buying time I get very strongly reassured, rightly or wrongly, by negative inflammatory markers." Male GP partner, 7 years’ experience.

Normal or significantly elevated inflammatory markers are seen as helpful but mildly raised inflammatory markers in the context of non-specific symptoms are difficult to interpret. Clinicians describe a tension between not wanting to ‘miss anything’ and, on the other hand, being wary of picking up borderline abnormalities which can lead to cascades of further tests. Diagnostic uncertainty is a common reason for inflammatory marker testing, aiming to reassure, however paradoxically inconclusive results can generate a cycle of uncertainty and anxiety.

Consequences

Clinicians should consider potential pitfalls of inflammatory marker testing and think about how they will use the results before requesting the tests. Further research is required to help clinicians interpret raised inflammatory markers in primary care. Previous studies usually start with a single disease and estimate the probability of a raised inflammatory marker. However, clinicians start with a test result and need evidence to help them predict the probability of a wide range of possible diseases.

The issues raised may be relevant to other tests which can be used as tests of exclusion for patients with non-specific symptoms, and raises wider issues about laboratory testing in primary care.