Cranfield, Benjamin; (2023) Primary care blood tests: Understanding how we can support GP decision-making for patients presenting with new symptoms of possible cancer. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Background: Appropriately suspecting the diagnosis of cancer is often challenging. Half of all patients subsequently diagnosed with cancer present with non-specific symptoms, and for those patients diagnostic strategies to aid GP decision-making are limited. Recent evidence indicates that common blood tests may have diagnostic utility for predicting cancer, where their diagnostic utility relies on their effective use. Aim: The purpose of this PhD is to generate evidence that identifies the correlates of the use of common blood tests for suspected cancer in primary care as a first step in identifying the potential for their optimal use. To facilitate this, the research objectives are to better understand: • How often common blood tests are used in patients subsequently diagnosed with cancer and how patient characteristics and symptom types predict greater or lower use • The key factors (other than the clinical presentation per se) that influence blood test use in patients presenting with possible cancer symptoms. Method: 1. Using a quantitative approach and using data from the National Cancer Diagnosis Audit, I explored variation in common blood test use in English general practice for patients subsequently diagnosed with cancer and examined different patient and clinical factors associated with the diagnostic process. I further explored variation in blood test use by presenting symptoms in a subsequent quantitative analysis of nine primary care blood tests. 2. Using a qualitative approach I explored non-clinical presentation influences on GP’s use of blood tests for suspected cancer. Social cognitive theory using the Situativity Perspective Framework guided the development of semi-structured interview schedules to elicit GP perceptions about contextual elements of blood testing. Thematic analysis allowed for an in-depth assessment of the blood testing process, illuminating external barriers to testing that previously have received relatively less attention than those arising during patient and GP interactions. Results: Certain patient groups and cancer sites are associated with greater or lower use of blood tests. Symptom categories, and individual presenting symptoms are associated with large variability in general use of blood testing, and that of individual blood tests. The findings indicate both the possible higher than expected use of blood tests in patients with alarm symptoms, and their possible under-use in those presenting with symptoms of lower specificity. A range of contextual barriers other than GPs knowledge in response to specific clinical presentations have been identified as influencing decisions about the use of blood tests, including the organisation of the phlebotomy service and patient expectations for blood tests. There is scepticism among GPs about the usefulness of point-of-care blood tests that are analogues to those currently commonly used. Implications: This PhD generated evidence to help translate the promising evidence supporting the diagnostic utility of common blood test use for early cancer diagnosis. The research identifies patient groups in whom blood tests may be underused (and others where over-testing may be occurring); it highlights the importance of optimising the total testing process for blood testing and identifies the need for further research into mitigating barriers to blood test use. Through addressing logistical and practical barriers to blood testing, GPs may be better supported in making greater use of blood tests as a diagnostic strategy for patients who present with non-specific symptoms.

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