Orthostatic hypotension is a bit of a tough issue, given that we think of it as a binary diagnosis (yes this patient is orthostatic, or no they are not), when in fact its syndrome is very much dependent on continuous variables. That's not to say that orthostasis is an exception in this regard, as we do this quite frequently. Picking the best spot on the ROC curve to maximize your test characteristics seems like a common thing we do.
Today, we discussed a very rare cause of orthostatic hypotension, that being carcinomatosis/paraneoplastic autonomic neuropathy. This is a common problem however, and so we should approach it with as much precision as we can muster. Precision comes from evidence, whether that be personal (anecdotal) or from the literature (observational/experimental), but the evidence we have to guide diagnostics around orthostatic hypotension is pretty thin, and mostly around hypovolemia associated orthostatic hypotension, rather than other causes. So, I will discuss orthostasis as it is relevant to hypovolemia.
Really, there are three things to think about when diagnosing orthostatic hypotension: 1) postural symptoms, 2) blood pressure, and 3) heart rate. In descending order, the most helpful vital sign abnormalities when suspecting hypovolemia-related orthostasis are as follows: 1) supine hypotension/tachycardia, 2) postural sustained increase in HR by >30 bpm or severe postural dizziness, 3) postural decrease in SBP by >20mmHg associated with any dizziness. Severe postural dizziness is essential dizziness that precludes completion of the test.
Some practical tips: a) your MA/nurse may not check HR with the BP at each vital sign check, but this is necessary, and b) supine-->sitting vital sign changes are much, much less useful than supine-->standing.