Researchers found that abnormal results from commonly used blood tests may substantially improve the detection of underlying cancer in patients presenting with abdominal pain or bloating. The findings suggested that considering information from these blood tests in addition to the presenting symptoms, age, and sex could help identify more patients who should receive urgent cancer referrals.

In a population-based cohort study, published in PLOS Medicine, the researchers recruited 477,870 patients aged 30 years and older from England who presented to genera practice with new onset abdominal pain (n = 425,549) or abdominal bloating (n = 52,321) between 2007 and 2016. Led by Meena Rafiq, PhD, of the University College London, they analyzed data from the UK Clinical Practice Research Datalink linked to the National Cancer Registry, Hospital Episode Statistics, and Index of Multiple Deprivation. 

Among the key findings were:

• 2.2% of patients with either abdominal pain or bloating were diagnosed with cancer within 12 months. Risk exceeded the 3% threshold used by NICE for urgent referral in male and female patients older than 60 years.
• In patients aged 30 to 59 years, several blood test abnormalities increased the cancer risk above 3%, including raised inflammatory markers, low albumin, high platelets, and anemia.
• Compared with assessing cancer risk based only on symptoms, age, and sex, also considering blood test results in patients with abdominal bloating would generate 63 extra urgent referrals per 1,000 patients and identify 3 additional patients with cancer (16% increase in yield).

The researchers examined the positive predictive value (PPV) of 19 blood test abnormalities for cancer, stratifying by age and sex. The most strongly predictive were low albumin, high platelets, high prostate-specific antigen in male patients, and high CA125 in female patients. Two-thirds of the symptomatic patients had concurrent blood tests. Those with abnormal results had higher 12-month cancer incidence than the untested groups (e.g. 2.7% vs 1.5% for abdominal pain).

In female patients aged 50 to 59 years with abdominal bloating, cancer risk increased from 1.6% to 10% with raised ferritin, 9% with low albumin, 8% with raised platelets, 6% with raised inflammatory markers, and 4% with anemia. Across all ages, multiple abnormalities in blood counts, liver and kidney function, and tumor markers conferred a posttest risk of cancer ≥ 3%.

Negative predictive value, sensitivity, specificity, and likelihood ratios were also reported. Rankings of PPVs by cancer site for each abnormality were provided to guide the investigation, with a diverse range of cancer types associated with these symptoms. The most common sites were the colon, ovary, prostate, and pancreas.

The researchers noted potential health system implications of increased phlebotomy and specialist service demand. Clinical decision support tools may assist clinicians with identifying relevant abnormalities. Study limitations included relying on coded symptoms and potential variation if blood test rates differed between settings.

"Commonly used primary care blood test results can improve the detection of underlying cancer in patients consulting with nonspecific abdominal symptoms," concluded the study authors. The findings may inform updates to referral guidelines and investigation strategies for earlier cancer diagnoses.

Full disclosures are available in the study.