BMJ Open · Oct 26, 2026

Cancer incidence following platelet count and C-reactive protein testing across ethnic groups in English primary care: a cohort study of 5 million patients

By Barlow M, Down L, Mounce LTA et al.

OBJECTIVES: To investigate whether the association between platelet count or C-reactive protein (CRP) results and 1-year cancer incidence varies by patient ethnicity. DESIGN: Cohort study using routinely collected health records from the Clinical Practice Research Datalink Aurum, Hospital Episode Statistics Admitted Patient Care and National Cancer Registration and Analysis Service. SETTING: English primary care, with linkage to secondary care records and national cancer registry data. PARTICIPANTS: Patients aged 40 years or older with a recorded ethnicity, no previous malignancy, and a platelet count or CRP test recorded between 1 January 2010 and 31 December 2017. Ethnicity was categorised as white, Asian, black, other or mixed. PRIMARY AND SECONDARY OUTCOME MEASURES: The primary outcome measures were 1-year cancer incidence following platelet count or CRP testing and variation in the association by ethnicity. Secondary outcome measures were 1-year site-specific cancer incidence and stage at diagnosis. RESULTS: The study included 4 901 450 patients with a platelet count record and 811 559 with a CRP record. One-year cancer incidence was highest among white patients and lowest among Asian patients. Following a normal platelet count, 1-year cancer incidence was 1.3% (95% CI 1.3 to 1.3%) for white patients and 0.63% (0.60 to 0.66%) for Asian patients; following thrombocytosis, incidence increased to 3.9% (3.8 to 4.0%) and 1.8% (1.5 to 2.1%), respectively. After a normal CRP result, cancer incidence was 1.5% (1.4 to 1.5%) for white patients and 0.81% (0.73 to 0.90%) for Asian patients, rising to 3.6% (3.5 to 3.7%) and 1.9% (1.7 to 2.2%) for a high CRP result, respectively. No significant interactions were found between ethnicity, blood test result and overall cancer diagnosis, and similar ORs were observed across all ethnic groups. However, for colorectal cancer, black patients with abnormal results showed higher ORs compared with white patients, relative to a normal result. The OR for thrombocytosis was 11.1 (7.8 to 15.6) for black patients versus 5.7 (5.4 to 6.0) for white patients (interaction p value<0.001), and for raised CRP was 4.1 (2.6 to 6.6) for black patients versus 2.5 (2.3 to 2.7) for white patients (interaction p value=0.043). CONCLUSIONS: This large primary care study provides reassurance that thrombocytosis and raised CRP appear to have broadly consistent associations with 1-year cancer incidence across ethnic groups in UK primary care.

doi.org/10.1136/bmjopen-2026-120128Open accessPubMed 42933828Biomarkers