Higher end of normal blood platelet count may indicate cancer

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Blood platelet counts at the higher end of normal suggest a high risk of cancer in men aged 60 or over, and should be investigated, according to University of Exeter research. Platelets perform a crucial function in blood, including helping blood to clot, which helps us heal wounds. However, Exeter researchers have previously found that cancer risk is significantly raised by having an abnormally high blood platelet count (more than 400 x 109/l,) a condition known as thrombocytosis. Now, they have found that cases of cancer greatly increased in older males with a platelet count on the high end of normal range (326 to 400 x 109/l), indicating that these patients should be investigated for cancer.

In a study funded by NIHR, researchers reviewed the records of nearly 300,000 patients who had platelet counts on the higher end using data from the UK’s Clinical Practice Research Datalink and the National Cancer Registration and Analysis Service. They found that the number of these patients diagnosed with cancer a year later was significantly higher if the patients had even slightly raised platelet levels. Of 68,181 male patients with levels of blood platelet on the higher end of normal, 1,869 cases of cancer were diagnosed within one year. Of these, 720 were an advanced stage.

A higher platelet count was most frequently linked to lung and colorectal cancers – both aggressive forms of cancer.

Dr Sarah Bailey, senior research fellow at the University of Exeter Medical School who led the research, said: "After finding that having a blood platelet count above normal range put people at high risk of cancer, we investigated the risk at the high end of normal. We found that men aged over 60 whose platelet count is on higher end of a normal are more likely to have an underlying cancer. Updating guidance for GPs to investigate higher platelet counts could save lives. This is particularly important in a post-COVID era; clues to help GPs identify cancer earlier are crucial to target the backlog in cancer investigation and diagnosis"

Professor Willie Hamilton, of the University of Exeter Medical School, said: "The UK lags well behind other developed countries on early cancer diagnosis. Our findings on platelet count and cancer diagnosis can help to combat that lag. It is now crucial that we roll out cancer investigation of thrombocytosis. It could save hundreds of lives."

Background: A raised platelet count (thrombocytosis) measuring >400 × 109/l is associated with high cancer incidence. It is uncertain whether platelet counts at the upper end of the normal range (high-normal: 326–400 × 109/l) are also associated with cancer.
Aim: To investigate cancer incidence following a normal platelet count in primary care.
Design and setting: A prospective cohort study was undertaken using data from the Clinical Practice Research Datalink and National Cancer Registration and Analysis Service, dating from 1 May 2005 to 30 April 2014.
Method: One-year cancer incidence was estimated for 295 312 patients with normal platelet counts (150–400 × 109/l). Patients with platelet counts >325 × 109/l were oversampled to maximise precision of estimates of cancer incidence. All patients were aged ≥40 years with no prior cancer diagnoses. The effects of age, sex, and smoking were explored. Non-melanoma skin cancers were omitted from exclusions and incidence.
Results: One-year cancer incidence increased greatly with age, male sex, and higher platelet count. Males aged ≥60 years with a high-normal count had an incidence of 4.2% (95% confidence interval [CI] = 4.0 to 4.4). The highest incidence of 6.7% (95% CI = 5.3 to 8.4) was found in males aged ≥80 years, who had platelets in the range of 376–400 × 109/l; this was 3.1 percentage points higher than the incidence for patients in the same age group with lower-normal counts of 150–325 × 109/l. Risks for all female subgroups were <3%. Patients with high-normal platelet counts were most at risk of lung and colorectal cancers and, in general, had advanced-stage cancer at diagnosis.
Conclusion: Platelet counts at the high-normal range in males aged ≥60 years may be indicative of an underlying malignancy, and referral for further investigation should be considered.

Luke TA Mounce, Willie Hamilton, Sarah ER Bailey


University of Exeter material


British Journal of General Practice abstract

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