Correlation Between Activity Level of Renin-Angiotensin-Aldosterone System and Perfusion Index in Children with Postural Tachycardia Syndrome

To evaluate the relationship between Renin-Angiotensin-Aldosterone System (RAAS) activity and Perfusion Index (PI) in children with Postural Tachycardia Syndrome (POTS), and to assess the diagnostic performance of Angiotensin II (AngII) and PI for POTS status. A total of 65 children with POTS and 65 age- and sex-matched healthy controls were enrolled. Plasma renin, angiotensin I (AngI), AngII, and aldosterone were quantified via enzyme-linked immunosorbent assay, and PI was measured using a pulse oximetry-based monitor during head-up tilt testing. Statistical analyses included Receiver Operating Characteristic (ROC) curve analysis of AngII and PI for POTS status, binary logistic regression, and Pearson correlation. Compared to controls, children with POTS demonstrated a significantly lower PI (4.64 ± 1.54 vs 6.19 ± 1.64%; adjusted < 0.005) and higher AngII levels (114.07 ± 7.69 vs 109.20 ± 10.44 pg/mL; adjusted = 0.012). ROC analysis indicated that PI had a stronger diagnostic value (AUC = 0.753, 95% CI: 0.670-0.836) than AngII (AUC = 0.654, 95% CI: 0.559-0.749) in identifying POTS. In logistic regression, only PI remained an innt predictor of POTS (Odds Ratio = 0.577, 95% CI: 0.442-0.755, < 0.001). A significant inverse correlation was observed between AngII and PI (r = -0.459, < 0.001). PI is a valuable, noninvasive clinical marker for POTS in children, demonstrating superior diagnostic utility compared to AngII. While elevated AngII retains clinical significance by reflecting underlying pathophysiology and disease severity, its independent predictive value is limited. The combined assessment of PI and AngII may enhance the pathophysiological understanding and management strategies for pediatric POTS.