Please note: This information will be published on CPRD's website as part of its transparency policy
Platelets are involved in blood clotting. The normal range is 150 - 400 x 109/l, and a platelet count of over 400 x 109/l is known as thrombocytosis. Thrombocytosis was recently found to indicate increased risk of cancer: our previous CPRD-based study found that 11.6% of men and 6.2% of women were diagnosed with cancer within one year of having a blood test showing thrombocytosis.
UK guidance for diagnosing cancer in primary care advises GPs to refer patients for further investigation for suspected cancer if their symptoms suggest a 3% or greater risk of cancer. The risk of cancer far exceeds 3% for patients with thrombocytosis, suggesting that those with a platelet count at the upper end of the normal range may also be at increased risk.
The present study aims to:
1. Investigate the risk of cancer in patients with a high-normal platelet count.
2. Explore which cancers patients with high-normal counts are most at risk of, and the cancer staging at diagnosis.
3. Determine the platelet count at which patients exceed a 3% risk of cancer
We will do this by examining electronic medical records of patients with a platelet count in the normal range, and cancer registry records.
Thrombocytosis is a newly discovered risk marker of cancer. A recent study found that the one year cancer incidence was 11.6% (95% CI 11.0 - 12.3) in male patients with thrombocytosis and 6.2% (95% CI 5.9 - 6.5) in female patients with thrombocytosis.(1) The incidence of cancer exceeded 3% even at the lowest part of the abnormal range (platelet count of 400-424). These figures far exceed the 3% threshold set by NICE for rapid investigation of suspected cancer.(2) These points suggest that some patients with a platelet count in the upper end of the normal range may have an underlying malignancy associated with their higher platelet count.
The present study aims to investigate the risk of cancer in patients with a platelet count at the upper end of the normal range. It will utilise CPRD records linked to National Cancer Registry and Office of National Statistics data, using a prospective cohort study design. A stratified analysis will examine the one year incidence of cancer by platelet count group for patients in the high-normal range (326 - 350 x 109/l, 351 - 375 x 109/l, 376 - 400 x 109/l), and a comparison group in the remaining range of a normal count (150 - 325 x 109/l). The comparison group will enable us to account for any artefactual effect of having had a blood test. The analysis will be stratified by age and gender, as both of these are associated with developing cancer. Platelet count will also be examined as a continuous variable. The types of cancer most commonly diagnosed in these groups will be estimated, as well as the stage of disease. Further analyses will examine the platelet count level at which the risk of cancer exceeds the 3% threshold set by NICE.
Cancer diagnosis
- Cancer incidence
Luke Mounce - Chief Investigator - University of Exeter
Luke Mounce - Corresponding Applicant - University of Exeter
Gary Abel - Collaborator - University of Exeter
Sarah Bailey - Collaborator - University of Exeter
William Hamilton - Collaborator - University of Exeter
NCRAS Cancer Registration Data;ONS Death Registration Data