How can you distinguish cell death from reduced proliferation in a viability assay?

Why

Imagine two cultures start with 10,000 live cells. After 72 hours the vehicle has 80,000, but the treated sample has 12,000. The endpoint treated-to-control ratio looks small even though treated cells still slightly increased.

That is strong growth inhibition, not direct evidence of killing. Compare the treated count with its time-zero count and collect longitudinal live or dead counts, imaging or a validated membrane-integrity marker. Apoptosis markers can add mechanistic detail but may miss other modes of death and depend on sampling time.

Growth-rate-normalized dose-response metrics can reduce bias caused by different untreated division rates. ATP luminescence may shift with metabolism or compound interference, so confirm with an orthogonal modality. Interpret a concentration series using starting density, exposure time and biological replicates rather than calling every low viability value cytotoxic.