REN and chronic kidney disease: Baseline NP levels may have been affected by population characteristics such as age, HF symptoms, medications (for example, diuretics and renin–angiotensin system antagonists), and other medical conditions including chronic kidney disease and atrial fibrillation.24 These covariates were not stratified for as the aim was to explore test accuracy for guideline referral thresholds, and both ESC and NICE do not currently have differing thresholds based on other factors.