Improving the Clinical Utility of Platelet Count for Cancer Detection in Primary Care: A Cohort Study in England, Canada, and Australia.

Simple Summary: The platelet count is an established marker of cancer. In healthy populations, platelet count varies by age and sex; despite that variation, a single reference range is used. This study aimed to identify age- and sex-specific upper thresholds for platelet count at which cancer should be considered in primary care, using audits of primary care-based clinical data in England, Canada, and Australia. Across all three cohorts, there was a clear upwards trend in cancer incidence with increasing platelet count for both sexes and at all age groups. The appropriate threshold will vary by country and will depend on local healthcare needs and priorities. As colorectal and lung cancers predominate, initial investigation may target these sites. Further investigation, depending on the patient's symptoms, could be CT imaging, endoscopy, or CA125. The platelet count, a component of the full blood count, has been identified as a useful diagnostic marker for cancer in primary care. The reference range for the platelet count is 150 to 400 or 450 × 109/L; this range does not account for natural variation in platelet count by age and sex. This study used three primary care cohorts from England, Canada, and Australia. Patients aged 40 years and over with a full blood count were included and stratified by age (in 10-year bands), sex, (male/female), and platelet count group. Cancer incidence within one year of the test date was estimated from linked registry data. In all three countries, there was a clear upwards trend in cancer incidence with increasing platelet count for both sexes and at all age groups. Lung and colorectal were the most common sites. These results have important implications for the international application of this work; analysis of local health datasets will be crucial to determining appropriate thresholds. Appropriate upper thresholds will depend on local populations, healthcare needs, and priorities. Further research is needed to assess the likely impact of new recommendations on the healthcare system, on cancer outcomes, and patient benefit. [ABSTRACT FROM AUTHOR]