Gobburu (2009) points out that biomarkers can act as surrogates for drug development decisions without having to be surrogates for regulatory approval. The scientific concerns of surrogacy remain the same but the degree of accuracy / risk-reward will be different.

Changes in fasting plasma glucose or international normalized ratio (INR) are good surrogates for dose selection but not for regulatory approval.

Caveat: A lot has changed since 2009 since we expect many more tools for evaluating drugs go through a qualification process now.