Correlation between activity level of renin-angiotensin-aldosterone system and perfusion index in children with postural tachycardia syndrome

Objective To investigate the correlation between Renin-Angiotensin-Aldosterone System (RAAS) activity and Perfusion Index (PI) in children with Postural tachycardia syndrome (POTS). The diagnostic value of angiotensin II in predicting hypoperfusion in children with POTS was evaluated. Methods Thirty children with POTS diagnosed by Head-Up Tilt Test (HUTT) in the First Affiliated Hospital of Shihezi University from August 2024 to April 2025 were selected as the POTS group, and 30 healthy children in the same period were selected as the control group. The levels of renin, angiotensin I, angiotensin II and aldosterone were measured in the 60° tilt position, and the PI value was monitored by pulse oximeter. Spearman correlation analysis was used to evaluate the correlation between angiotensin II and PI. Receiver Operating Characteristic (ROC) was used to evaluate the diagnostic efficacy of angiotensin II in predicting hypoperfusion. Results The level of angiotensin II in POTS group was significantly higher than that in control group (P = 0.016), and the value of PI was significantly lower than that in control group (P = 0.029). There were no significant differences in the levels of renin, angiotensin I and aldosterone between POTS group and control group. There was a moderate negative correlation between angiotensin II and PI (ρ = -0.389, P = 0.034). ROC curve analysis showed that the area under the curve (AUC) of angiotensin II for predicting hypoperfusion was 0.76, the best cut-off value was 131.06 pg/mL, the sensitivity was 64.29%, and the specificity was 87.5%. Conclusions Angiotensin II level has a certain predictive value for hypoperfusion in children with POTS, and there is a significant negative correlation between angiotensin II level and perfusion index. The combined evaluation of RAAS system activity and PI is expected to be an auxiliary method for noninvasive evaluation of hemodynamic status in POTS. Clinical trial number: not applicable