Background: Multiple myeloma is a haematological cancer characterised by numerous non-specific symptoms leading to diagnostic delay in a large proportion of patients.
Aim: To identify which blood tests are useful in suggesting or excluding a diagnosis of myeloma.
Design and setting: A matched case-control study set in UK primary care using routinely collected data from the Clinical Practice Research Datalink.
Method: Symptom prevalence and blood tests were analysed up to 5 years before diagnosis in 2703 cases and 12 157 matched controls. Likelihood ratios (LR) were used to classify tests or their combinations as useful rule-in tests (LR+ = ≥5), or rule-out tests (LR- = ≤0.2).
Results: Raised plasma viscosity (PV) had an LR+ = 2.0, 95% confidence interval [CI] = 1.7 to 2.3; erythrocyte sedimentation rate (ESR) 1.9, 95% CI = 1.7 to 2.0; and C-reactive protein (CRP) 1.2, 95% CI = 1.1 to 1.4. A normal haemoglobin had an LR- = 0.42, 95% CI = 0.39 to 0.45; calcium LR- = 0.81, 95% CI = 0.78 to 0.83; and creatinine LR- = 0.80, 95% CI = 0.77 to 0.83. The test combination with the lowest LR- was all normal haemoglobin with calcium and PV, which had an LR- = 0.06, 95% CI = 0.02 to 0.18, though the LR- for normal haemoglobin and PV together was 0.12 (95% CI = 0.07 to 0.23).
Conclusion: Plasma viscosity and ESR are better for both ruling in and ruling out the disease compared with C-reactive protein. A combination of a normal ESR or PV and normal haemoglobin is a simple rule-out approach for patients currently being tested in primary care.
Keywords: blood; case–control studies; diagnosis; inflammatory; multiple myeloma; primary care.
© British Journal of General Practice 2018.