Screening for primary aldosteronism: The “PA” Shiny app

Primary aldosteronism (PA) is the most frequent cause of secondary hypertension and is characterised by excess of aldosterone despite suppressed renin.^1,2 Prevalence estimates for PA range from 3.2 to 12.7% in patients with hypertension in primary care. ³ Patients with PA have worse cardiovascular outcomes than patients with blood pressure-matched essential hypertension. ⁴ Targeted treatment with adrenalectomy for unilateral disease, or mineralocorticoid receptor antagonist for bilateral disease, improves blood pressure and ameliorates the cardiovascular risks associated with aldosterone excess. ⁵ Early detection of PA in the primary care settings is therefore crucial. ² Plasma aldosterone-renin ratio (ARR) is currently the recommended screening test. ⁶

Commonly used antihypertensive medications, hypokalaemia and reduced kidney function may all affect the ARR and reduce the accuracy of screening.^6,7 Ideally, interfering drugs should be replaced with non-interfering antihypertensive agents.^6,7 ARR results must be carefully interpreted in the setting of interfering medications. ⁷

In a recent qualitative study exploring why Australian primary care physicians screen for PA, the findings suggest that knowledge gaps, practical limitations of the ARR, and errors in diagnostic reasoning were challenges of routine PA screening. ² Most of these practical barriers could be addressed by “relatively simple educational and practice modifications to increase PA screening rates and optimise detection for the most common cause of secondary hypertension in primary care”. ²

Shiny is an R package that makes it easy to build interactive web apps straight from R. ⁸ We developed pilot Shiny apps to assist clinicians in preparing the patient for ARR and to guide the interpretation of ARR. For the first app on patient preparation for ARR (https://aldosterone-to-renin-ratio.shinyapps.io/ARR_Preparation/), a list of medications is available for user selection. This leads to specific advice on the selected medication and, if required, a table of medications that do not affect screening, and how to use them. In the second app on interpreting ARR (https://aldosterone-to-renin-ratio.shinyapps.io/ARR_Interpretation/), the user enters a value for serum potassium, eGFR, aldosterone/renin ratio and selects an aldosterone assay used at the pathology provider. A list of medications is once again available for user selection. Depending on the laboratory values, aldosterone assay and medications, the relevant comment appears. The ARR thresholds are based on current practice at laboratories in Australia.

The apps are a guide only and do not substitute for clinical judgment or specialist advice. The apps can be refined as newer medications become available or following updates of professional guidelines. We aware of online applications such as MDCalc ⁹ and QxMD, ¹⁰ but to the best of our knowledge, these pilot Shiny apps are the first apps to assist in screening for PA, including preparing for and interpreting plasma ARR. While there are existing detailed resources on ARR preparation and interpretation, the apps are unique in that they provide busy clinicians with almost instant guidance on how to approach ARR. Prospective studies involving clinicians are required to determine if the apps increase screening rates and lead to better health outcome for patients subsequently treated for PA. Similar apps can be developed for conditions such as Cushing’s syndrome and adrenal insufficiency.