MONITORING OF POTASSIUM AND eGFR FOLLOWING RENIN ANGIOTENSIN SYSTEM INHIBITOR INITIATION – NECESSARY SAFETY GUIDELINE, OR COSTLY LIMIT TO OPTIMISING BP TREATMENT IN UK PRIMARY CARE?

Chronic kidney disease (CKD) is a critical public health challenge in the UK. Around 2% of those living with CKD progress to end-stage kidney disease (ESKD), however all are at increased cardiovascular risk. Renin-angiotensin system inhibitors (RASi) are a key pillar of treatment for blood pressure and proteinuria in the context of CKD.  

The UK National Institute of Clinical Excellence advocates monitoring for hyperkalaemia and eGFR 1-2 weeks following initiation and any dose change of RASi, starting with a low dose and titrating to the maximum tolerated dose. This is time consuming for patients and health care staff.

We evaluated the impact of RASi optimisation on potassium, eGFR, adverse events as well as undertaking economic modelling of the attendant costs.

The study area was the Living Well Partnership (LWP), a primary care network (PCN) in Southampton, population 46,500 patients, including areas of significant socioeconomic deprivation. 

Using fully anonymised, routinely collected primary care data, we evaluated the timing and frequency of blood tests, change in potassium and eGFR after initiation of RASi, as well as any resultant adverse events e.g. hospital admission. We made an estimate of the costs to primary care of optimisation of RASi using local costings for consumable clinical resources and workforce estimates.  

Paired t-tests were used to evaluate changes in blood test parameters before and after initiation of RASi.

Between August 5, 2022, to February 5, 2024, 876 patients were started on RASi. The median eGFR was 80ml/min/1.72m2. Only 20.1% of patients had a blood test within 28 days of starting or increasing the dose of RASi.

The mean change in potassium was 0.1 mmol/L (sd 0.39) and mean change in eGFR was -1.11 ml/min.  No patients had hyperkalaemia (K>6 mmol/L) or a significant decline in eGFR (>30% reduction from baseline).

The average BP at the last prescribed dose was 130 mmHg systolic for those on ACEi, and 131 mmHg systolic for those on ARB.

The cost of full optimisation (clinician, administrative and equipment) was estimated to be between £69.60-103.83 per patient optimised on ACEi (using Ramipril as an exemplar) and £54.55-82.58 for each patient optimised on ARB (using Losartan as an exemplar) – an average of £77.64/patient. The variability in costs was dependent on which healthcare professional performed each review (i.e. nurse/pharmacist/GP).

Therefore, for a PCN of similar size to LWP, for 876 patients this represents an annual cost of around £68,012. This does not consider the cost of the patient’s time, community pharmacist time, wastage in medications during optimisation, or the environmental burden of appointment attendances (average 5-6/patient).

The guideline mandated monitoring of potassium and eGFR following initiation/dose change of RASi is time consuming.  The cost of monitoring, in terms of financial, environmental and primary care team time, is significant.  In this cohort, concordance with the guideline was low. We did not identify any patients who had a significant safety event, and the overall change in potassium and eGFR was small.

We propose that research in larger cohorts is undertaken to enable guidelines to be refined for a risk stratified, cost effective approach for repeat testing of eGFR and potassium after RASi initiation.

This abstract was presented at the UK Kidney association meeting in 2025.