Primary care blood tests before cancer diagnosis: National Cancer Diagnosis Audit data

Blood tests can support the diagnostic process in patients with cancer but how often they are used is unclear.

To explore use of common blood tests before cancer diagnosis in primary care.

English National Cancer Diagnosis Audit data on 39 752 patients with cancer diagnosed in 2018.

Common blood test use (full blood count [FBC], urea and electrolytes [U&E], and liver function tests [LFTs]), variation by patient and symptom group, and associations with the primary care interval and the diagnostic interval were assessed.

At least one common blood test was used in 41% (n = 16 427/39 752) of patients subsequently diagnosed with cancer. Among tested patients, (n = 16 427), FBC was used in 95% (n = 15 540), U&E in 89% (n = 14 555), and LFTs in 76% (n = 12 414). Blood testing was less common in females (adjusted odds ratio versus males: 0.92, 95% confidence interval [CI] = 0.87 to 0.98) and Black and minority ethnic patients (0.89, 95% CI = 0.82 to 0.97 versus White), and more common in older patients (1.12, 95% CI = 1.06 to 1.18 for ≥70 years versus 50-69 years). Test use varied greatly by cancer site (melanoma 2% [ n = 55/2297]; leukaemia 84% [ n = 552/661]). Fewer patients presenting with alarm symptoms alone were tested (24% [ n = 3341/13 778]) than those with non-alarm symptoms alone (50% [ n = 8223/16 487]). Median primary care interval and diagnostic interval were longer in tested than non-tested patients (primary care interval: 10 versus 0 days; diagnostic interval: 49 versus 32 days, respectively, P<0.001 for both), including among tested patients with alarm symptoms (primary care interval: 4 versus 0 days; diagnostic interval: 41 versus 22 days).

Two-fifths of patients subsequently diagnosed with cancer have primary care blood tests as part of their diagnostic process. Given variable test use, research is needed on the clinical context in which blood tests are ordered.