A cheap tablet that blocks clot-forming blood cells. It lowers heart attacks and clot-driven strokes in people with already narrowed arteries, less so in those without, cuts repeat vein clots, and lowers bowel cancer after at least five years. Against this: more gut and brain bleeding, slow iron loss, and an unexplained rise in deaths when started after seventy. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Haemoglobin | 135–160 g/L (men), 120–150 g/L (women) | Detects chronic occult blood loss |
| Ferritin | 50–150 µg/L | Iron stores deplete before haemoglobin falls |
| Platelet count | 200–350 × 10⁹/L | Thrombocytopenia makes aspirin unsafe |
| Faecal immunochemical test | Negative | Detects occult bleeding and the lesion it may mask |
| Serum uric acid | 210–360 µmol/L (3.5–6.0 mg/dL) | Aspirin blocks urate secretion; can precipitate gout |
| Estimated glomerular filtration rate | Above 60 mL/min/1.73 m², stable year to year | Falling filtration raises bleeding risk |
| Blood pressure | Below 120/80 mmHg | Main modifiable driver of brain bleeding on aspirin |
| High-sensitivity C-reactive protein | Below 1.0 mg/L | Inflammatory risk enlarges expected benefit |
| Lipoprotein(a) | Below 75 nmol/L (30 mg/dL) | Identifies the clot-prone phenotype most likely to benefit |
| Coronary artery calcium score | 0 under age 60; above 60 track change from prior scan | Best single discriminator of who gains more than they lose |
| Helicobacter pylori stool antigen | Negative | Colonisation multiplies ulcer-bleeding risk on aspirin |
Cadence: Full blood count and ferritin at 3 and 12 months, then every 1–2 years; blood pressure every 6 months; kidney function and faecal immunochemical test annually.