In this observational cross-sectional study, we investigated predictors of orthostatic intolerance (OI) in adults reporting long COVID symptoms. Participants underwent a 3-min active stand (AS) with Finapres^® NOVA, followed by a 10-min unmedicated 70° head-up tilt test. Eighty-five participants were included (mean age 46 years, range 25-78; 74% women), of which 56 (66%) reported OI during AS (OI_AS). OI_AS seemed associated with female sex, more fatigue and depressive symptoms, and greater inability to perform activities of daily living (ADL), as well as a higher heart rate (HR) at the lowest systolic blood pressure (SBP) point before the first minute post-stand (mean HR_nadir: 88 vs. 75 bpm, P = 0.004). In a regression model also including age, sex, fatigue, depression, ADL inability, and peak HR after the nadir SBP, HR_nadir was the only OI_AS predictor (OR = 1.09, 95% CI: 1.01-1.18, P = 0.027). Twenty-two (26%) participants had initial (iOH) and 5 (6%) classical (cOH_AS) orthostatic hypotension, but neither correlated with OI_AS. Seventy-one participants proceeded to tilt, of which 28 (39%) had OI during tilt (OI_tilt). Of the 53 who had a 10-min tilt, 7 (13%) had an HR increase >30 bpm without cOH_tilt (2 to HR > 120 bpm), but six did not report OI_tilt. In conclusion, OI_AS was associated with a higher initial HR on AS, which after 1 min equalised with the non-OI_AS group. Despite these initial orthostatic HR differences, POTS was infrequent (2%). ClinicalTrials.gov Identifier: NCT05027724 (retrospectively registered on August 30, 2021).

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