Should we test for primary aldosteronism (PA)?
NOTE: These blog posts are written from the perspective of a GP colleague who still seems to accumulate a list of unanswered questions at the end of each day in practice. Each post describes how I went about trying to answer the specific questions. These posts are not intended to be used for specific clinical guidance but hopefully provide links to some useful resources which the registrar can explore for themselves.
Should we test for primary aldosteronism (PA)?
This was the article in the medical press which stimulated my questions but still left some unanswered http://medicalrepublic.com.au/role-primary-care-primary-aldosteronism/17278 It referred to the July 2018 MJA article by Yang J,Fuller PJ & Stowasser M entitled “Is it time to screen all patients with hypertension for primary aldosteronism?” It seemed that this was currently the topic of the day as the other helpful article appeared in the October 2018 Australian Journal of General Practice (AJGP) by Lim YY et al titled “Current pattern of primary aldosteronism diagnosis: delayed and complicated”.
The Endocrine Society (2016) guidelines to help decide which patients will benefit from screening for PA https://www.endocrine.org/guidelines-and-clinical-practice/clinical-practice-guidelines/primary-aldosteronism include the usual suggestions:
- A sustained BP above 150/100 mmHg on repeated measurements
- Uncontrolled hypertension (BP>140/90 mmHg) despite at least three anti-hypertensives, including a diuretic
- Controlled hypertension (BP<140/90 mmHg) on at least four antihypertensive agents
- Hypertension and spontaneous or diuretic-induced hypokalaemia
- Hypertension and an adrenal incidentaloma
- Hypertension and sleep apnoea
- Hypertension and a family history of early-onset hypertension or cerebrovascular accident Hypertension and a first-degree relative with confirmed primary aldosteronism
I wasn’t sure how many of my patients these might apply to. Sometimes the repeated high measurements are explained away as white coat hypertension (or seeing another doctor); we sometimes inherit patients already on multiple medications; I could easily be missing sleep apnoea in some of my patients.
Some points I noted from the articles were that
- Maybe 6% of resistant hypertensives in primary care have PA
- But maybe half of PA actually have “mild” hypertension
- Rx outcomes are better in younger patients
- GPs see most new diagnoses but rarely investigate for PA
- Aldosterone: Renin Ratio (ARR) costs $43.70 (we need economic modelling as to cost-effectiveness re its use in primary care)
To be honest I can only think of a couple of patients with the diagnosis in my practice. One had a rather classic history but had been under specialist treatment for years. Finally, the “incidentaloma” was revealed. The AJGP article noted that in the study discussed (in the context of the Endocrine Hypertension Service), “The average duration of hypertension before referral was 13.5 years. The data show that 71% of patients had hypertension for at least five years, 61% had hypertension for at least 10 years and 38% had hypertension for at least 15 years. Twenty per cent of patients had hypertension for one to two years.” I wasn’t feeling too bad but I was wondering how many more I may have missed. It is, however, difficult to get good figures on how prevalent PA is in primary care. Again the articles note that PA
- Is probably more prevalent than previously thought
- Has a higher risk of adverse outcomes (so worth identifying)
- Is treatable (again, worth identifying)
- Only has hypokalaemia in 20% of cases (so not as obvious as previously thought)
Of course the main problem is that it is also complicated to check for aldosteronism once the patient is on treatment and this often involves ceasing or substituting medications prior to testing. The ARR has its own limitations with factors such as posture, time of sampling and dietary salt intake influencing it along with various hypertensives – ACE, ARBs, diuretics, beta blockers and some Ca blockers. There are differences of opinion in the literature about the need to stop or change medications but the general advice from the Endocrine Society is to do so.
As with other occasions on which we try to decide whether to screen for something in primary care it is important to consider that the predictive value of a diagnostic test depends on the prevalence of the condition in the population screened and the true prevalence in primary care is not clear as yet. Importantly, a lower prevalence will result in a higher rate of false-positive results.
I rarely seem to see patients with new onset hypertension these days. However, it did happen a few weeks ago and I did indeed check the ARR in that instance along with my usual management steps (it was normal). What will be our practice in the future? It is certainly worth revisiting some of those established hypertensive patients who may fit into the categories suggested by the endocrine society and who occasionally languish unobserved in general practice.
Here are the two articles which are well worth reading for more detail so that you can then decide how to implement this in your own practice in the future.
Perhaps some GP guidelines will be forthcoming.