Is the Aldosterone:Renin Ratio Truly Reproducible?

To the Editor: Rossi et al recently concluded that the aldosterone:renin ratio (ARR) is reproducible.1 However, we think that several common errors were performed in their data interpretation, as described below. In the Bland-Altman plot B (Figure 1 in Reference 1), the large differences in repeat measurements are overlooked on the basis that only 7% of points lay outside of the between-test “95% CIs,” by which they imply the Bland-Altman “limits of agreement.” These are constructed using the mean difference ±1.96 SDs, and so by definition alone, will always contain ≈95% of …