Rapidly quantifiable blood-based biomarkers of pain, sampled in...

Rapidly quantifiable blood-based biomarkers of pain, sampled in a non-invasive manner and analyzable using a locally held device (i.e. in an aged-care facility) are DECADES away. If they ever eventuate, the cost will be extremely prohibitive. If the cost is not prohibitive, pain, as defined by your cited article is "a subjective experience", meaning that there are innumerable factors that determine the severity of pain someone experiences that cannot be explained by biology alone. Meaning that blood-based biomarkers will still have measurement error, measurement error that subjective assessments of pain experience (captured by facial expressions and other behaviours) will partly explain. Therefore, the best measurement of pain will be multidomain.

I swore to myself that I wouldn't engage with you on this topic, because you're clearly not here to share ideas and communicate effectively, but here we are. You're oblivious.