Summary note on staging for COVID-19.

This list is not definitive. Just heuristics.

Many authors draw the mild/moderate division around where the patient will soon need oxygen support, SpO2 nearing 90-92% on room air.

Others take a less aggressive stance.

I use the former. https://twitter.com/__ice9/status/1330342402289258497

The less aggressive usually draw the moderate/severe line based on need for oxygen support. However, this labels most hospital cases severe, losing granularity. Some add a 'critical' category to compensate, but this is an overloaded term.

In discussions here, I draw the moderate/severe line around onset of hypoxemia on high-flow oxygen, often onset of pulmonary microthrombosis and soon rising D-dimer, with a high risk of ARDS and DAD but not quite there yet. This matches my reading of the literature.

This thread is mostly for context in later discussions, as the issue seems to arise fairly often.