Understanding acceptable thresholds helps prevent unnecessary discontinuation of guideline-directed therapy.
A patient with chronic kidney disease (CKD) and hypertension is started on sacubitril/valsartan (Entresto).1 Two weeks later, repeat labs show a rise in serum creatinine from 1.5 mg/dL to 1.85 mg/dL—a 23% increase from baseline—and a potassium level of 5.2 mmol/L. Despite improved blood pressure and no clinical symptoms, the medication is discontinued due to worsening renal function.
This scenario plays out daily across outpatient clinics and hospitals. In many cases, the laboratory changes prompting discontinuation are not signs of drug toxicity or treatment failure but predictable physiologic effects of renin–angiotensin–aldosterone system (RAAS) inhibition.2,3 Misinterpreting these changes can lead to premature discontinuation of therapies proven to reduce cardiovascular events, slow kidney disease progression, and improve survival.1-3
Mild increases in serum creatinine after starting an angiotensin converting enzyme (ACE) inhibitor, angiotensin receptor blocker (ARB), or angiotensin receptor-neprilysin inhibitor (ARNI) are often expected physiologic effects, not signs of kidney injury.4,5 Common ACE inhibitors include lisinopril, enalapril, and ramipril. Common ARBs include losartan, valsartan, and candesartan, and the primary ARNI currently available is sacubitril/valsartan (Entresto),1,4 which combines an ARB with a neprilysin inhibitor to enhance beneficial natriuretic peptides.
RAAS inhibitors dilate the efferent arteriole of the glomerulus, lowering intraglomerular pressure.4 This reduces glomerular hyperfiltration—a key mechanism that protects the kidney over the long term—but can temporarily decrease estimated glomerular filtration rate (eGFR) and raise serum creatinine.5
In other words, a small creatinine rise is hemodynamic, not nephrotoxic.4,5 It signals that the medication is working to relieve glomerular stress, not that the kidneys are failing. Health care professionals should contrast these expected changes with true acute kidney injury, which typically presents with rapidly progressive creatinine rise, oliguria or other clinical symptoms, and contributing factors such as volume depletion, nephrotoxins (for example, nonsteroidal anti-inflammatory drugs [NSAIDs]), or renal artery obstruction.5
Not all creatinine increases after RAAS inhibitor initiation warrant intervention. Multiple guidelines and clinical trials support tolerating a stable increase in serum creatinine of up to approximately 30% from baseline after starting or titrating an ACE inhibitor, ARB, or ARNI.2,3,5
In many cases, this rise reflects the expected hemodynamic effect of reduced intraglomerular pressure rather than kidney injury. When the increase is modest and stabilizes, continuing therapy is often appropriate and may confer long-term renal and cardiovascular benefit.1-3
More important than the absolute creatinine value is the trajectory. A small rise that plateaus over the first few weeks is typically benign, whereas a progressive or accelerating increase should prompt further evaluation.2,3,5
Clinicians should reassess therapy when creatinine rises exceed 30% from baseline or continue to worsen over time. In these situations, contributing factors should be evaluated before discontinuing RAAS inhibition, including volume depletion, excessive diuresis, use of NSAIDs, and hypotension.5 Less common but important considerations include bilateral renal artery stenosis.2,3
In the absence of symptoms, hypotension, or ongoing deterioration in kidney function, premature discontinuation of RAAS inhibitors based solely on modest creatinine increases may deprive patients of therapies shown to slow kidney disease progression and reduce cardiovascular risk.1-3
Mild increases in serum potassium are a predictable effect of RAAS inhibition.6 By reducing aldosterone levels, ACE inhibitors, ARBs, and ARNIs decrease renal potassium excretion, often resulting in small but measurable increases in serum potassium after initiation or dose escalation.6
Unlike creatinine, which tends to rise in a relatively predictable manner, potassium responses are less predictable.6,7 Factors such as baseline kidney function, diet, concomitant medications (NSAIDs, potassium supplements, or certain diuretics), and acid-base status can cause 2 patients on the same RAAS inhibitor dose to have very different potassium changes. For this reason, clinical guidance focuses on absolute potassium values and trends rather than percent change.6
In most patients, potassium elevations remain modest and manageable. Potassium levels up to approximately 5.5 mmol/L are commonly tolerated with continued therapy and closer monitoring, particularly when values stabilize rather than continue to rise. More concerning elevations—typically potassium levels above 5.6 to 6.0 mmol/L, or any elevation associated with electrocardiographic changes—warrant prompt intervention. Even in these cases, management should first focus on identifying and correcting reversible contributors before permanently stopping RAAS inhibition.6
Common contributors to hyperkalemia include excessive dietary potassium intake, potassium-containing salt substitutes, supplements, NSAIDs, worsening kidney function, and inadequate diuretic support. Addressing these factors often allows RAAS therapy to be continued safely. In select patients, adjunctive strategies such as diuretic optimization or potassium-binding agents may enable continued therapy while maintaining safe potassium levels.6
Certain populations are more likely to experience creatinine or potassium elevations that require closer monitoring2,3,6:
In these patients, closer monitoring is recommended, particularly within the first 1–2 weeks of initiation or dose adjustment.2,3,6
For most patients initiating or titrating RAAS inhibitors2,3,6:
This approach helps distinguish expected physiologic changes from early signs of kidney injury, allowing continued RAAS therapy whenever safe.
Matthew Richards, PharmD, is a community pharmacist with more than 20 years of experience focused on clinical evidence, medication safety, and evidence-based patient care. He also writes about practical pharmacy topics for professional audiences.
Mild increases in serum creatinine and potassium are common after starting ACE inhibitors, ARBs, or ARNIs2,3,6 and often reflect therapeutic hemodynamic effects rather than treatment failure. Recognizing which changes are expected, monitoring trends, and addressing reversible contributors enables clinicians to continue life-saving therapy safely.
By interpreting lab changes thoughtfully—rather than reflexively stopping therapy—pharmacists and clinicians can ensure patients receive the full renal and cardiovascular benefits of RAAS inhibition.1,2,3,6
