# Use the trend in routine blood counts, not a single threshold, to spot cancer

Source: https://onco.cc/ideas/idea-prev-blood-count-trend-flags/  
OnCo record `idea-prev-blood-count-trend-flags` (Idea). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

A platelet count that is normal but rising year on year, or haemoglobin drifting down, can signal cancer. Records already hold these trends; software could use them.

## Summary

Thrombocytosis and unexplained anaemia are known predictors; longitudinal within-person trends are more informative than population thresholds. Propose trend-based alerting in primary care (e.g. a 20% platelet rise over two years within the normal range), evaluated in a linked-data cohort and then an RCT.

## Fields

- Kind: Idea
- Last checked: 2026-09-08
- Hypothesis: Within-person trend flags identify at least 20% more incident cancers 6-12 months before diagnosis than threshold-based flags at the same alert rate.
- Rationale: Analogous to using individual baselines rather than population cut-offs in other fields; the data is already collected.
- Proposed test: Retrospective validation in CPRD or similar linked datasets (small cost); then a prospective pragmatic trial.
- Maturity: speculative
- Actor: data

## Sources

- Bottleneck evidence (The hardest cancers are found late): Crosby et al., Early detection of cancer (Science 2022): https://doi.org/10.1126/science.aay9040

## Connected records

- fronts: [Diagnostics & Biomarkers](https://onco.cc/fronts/diagnostics/), [Early Detection & Screening](https://onco.cc/fronts/early-detection/)
- bottlenecks: [The hardest cancers are found late](https://onco.cc/bottlenecks/b-early-detection/)
- key papers: [Early detection of cancer](https://onco.cc/key-papers/paper-crosby-science/)

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