Background Laboratory testing is an integral diagnostic tool, contributing to 70% of diagnoses in the NHS today. Its use has been steadily increasing despite estimates that ≤40% of blood tests ordered are unnecessary. Understanding blood-testing patterns is a fundamental step to tackling overuse.

Aim To characterise the volume, type, and per patient frequency (PPF) of venous blood testing reported in general practice in North West London, 2016–2018.

Method Following ethics clearance, aggregate data of blood tests reported in general practice in North West London between 2016 and 2018 were extracted from the Discover database. Non-venous blood test codes and codes not used within the designated time period were excluded. Codes reporting the same analyte were aggregated. Overall volume and PPF were calculated per analyte.

Results Three hundred and thirty-six individual analytes were reported and grouped into 35 recognised panels or groupings. Blood testing increased by 16.5% over the 3-year period. Full blood count, urea and electrolytes, liver function tests, and lipid profile accounted for 80.4% of all venous blood tests. Requests for HbA1c increased by 52.8% and non-HDL cholesterol by 148.7%, whereas glucose decreased by 13.3% and urea by 15.7%. The PPF remained unchanged over the 3-year period at 1.29 blood tests per person per year. The coagulation assay had the highest PPF at 3.0.

Conclusion Routine general practice data revealed important trends in blood testing. Trends uncovered can inform innovative and targeted solutions to reduce unnecessary blood testing.