Research methods
Surrogate endpoints vs clinical outcomes
Why HbA1c, body weight, MRI-PDFF and eGFR slope are surrogate endpoints and why MACE, kidney failure, hospitalisation and mortality are clinical outcomes.
Many trials use surrogates to demonstrate efficacy; outcome trials test whether those surrogates translate into clinically meaningful events.
What is a surrogate endpoint
A surrogate endpoint is a measurable biomarker or physiologic variable expected to predict a clinical outcome. HbA1c predicts diabetes complications; body-weight reduction predicts cardiometabolic improvement; MRI-PDFF predicts steatohepatitis trajectory; eGFR slope predicts kidney failure.
When surrogates and outcomes diverge
Surrogate-outcome relationships are population-derived and probabilistic, not deterministic. A treatment can improve a surrogate without improving the corresponding clinical outcome (and occasionally vice versa). This is why outcome trials remain the regulatory standard for outcome claims.
Practical reading
When a trial reports a surrogate result, ask: is there an outcome trial confirming the corresponding clinical benefit? For semaglutide and SELECT, that question has a clear answer for MACE-3 in the studied population; for many other comparisons it does not yet.
Key takeaways
- Surrogates are not outcomes.
- Surrogate-outcome relationships are probabilistic, not guaranteed.
- Outcome trials are the right standard for outcome claims.
- Formal statistical training.
- Individual treatment, prescribing or dosing advice.
- Permission to skip the original publication of any trial cited.
Sources are tagged by class. Regulatory documents, peer-reviewed publications and trial registry records are preferred. Manufacturer disclosures and conference material are accepted where peer-reviewed publication is not yet available; preprints are flagged.