Why Does eGFR Decline After Primary Aldosteronism Treatment?

A modest early decline in your estimated glomerular filtration rate (eGFR) is common after starting treatment for primary aldosteronism ^[1]. While it can be frightening to see a lower number on your lab report, this drop is often an anticipated change as your kidneys adjust to a normal hormone environment ^[2].

However, a drop in eGFR is not automatically harmless. A sudden, large, or continuing decline requires medical evaluation to rule out acute kidney injury, dehydration, or medication side effects ^[3].

When to Call Your Care Team

Contact your doctor promptly if you experience any of the following symptoms, and do not stop or change your treatment without clinician guidance:

• Fainting, severe dizziness, or very low blood pressure
• Markedly reduced urine output
• Inability to keep fluids down (such as severe vomiting or diarrhea)
• Severe weakness or palpitations (which can be signs of a potassium imbalance)

The “Unmasking” Effect

To understand why your eGFR might drop safely, it helps to know how excess aldosterone affects the body. Primary aldosteronism causes the kidneys to filter blood at an unusually high pressure—a state called hyperfiltration ^[2].

Treatments are designed to remove this excess hormone and relieve the pressure on your kidneys. This is typically done through surgery (adrenalectomy, usually for disease in just one adrenal gland) or medications called mineralocorticoid-receptor antagonists (MRAs like spironolactone or eplerenone, used when both glands are overactive or surgery is not pursued) ^[2].

When the high filtration pressure normalizes, your measured eGFR naturally falls to establish a new, post-treatment baseline ^[1]. Doctors call this the “unmasking” effect. The drop does not necessarily mean the treatment caused new kidney damage; rather, it often reveals preexisting kidney wear-and-tear that was previously hidden by the hyperfiltration ^[4][5]. This prior damage is often the result of prolonged high blood pressure and the direct vascular effects of primary aldosteronism ^[4].

In a combined analysis of patients after treatment (both surgery and medication), the average eGFR decrease was roughly 10.7 points (mL/min/1.73 m²) after about a year ^[1]. However, this is a group average, not a target or a prediction for every individual.

How Doctors Evaluate Your True Kidney Function

Because eGFR is an estimate that can fluctuate based on hydration, blood pressure, and medications, a single low reading does not automatically mean you have permanent chronic kidney disease (CKD). A CKD diagnosis generally requires an eGFR below 60 or signs of kidney damage persisting for at least three months, interpreted alongside your past lab results ^[6].

To get a full picture of your kidney health, your doctor will look at multiple factors. One common check is measuring the amount of protein leaking into your urine (albuminuria). Research shows that while eGFR may fall after treatment, albuminuria often improves once the hyperfiltration is stopped ^[7][1]. (Some specialized research studies also show that biological markers of kidney stress, like L-FABP and KIM-1, decrease after treatment, further supporting that the eGFR dip often represents a healthy relief of pressure ^[7]).

Long-Term Monitoring and Medication Safety

For many patients, the decline in eGFR happens early in treatment and then stabilizes into a new baseline ^[8][9]. Ongoing monitoring is essential to ensure it stays stable.

• Follow a monitoring timeline: Your clinician will commonly check your creatinine/eGFR, potassium, and blood pressure soon after starting treatment, after any medication dose changes, and at individualized intervals long-term ^[10].
• Medication adjustments: If you take an MRA, your doctor will individualize your dose based on a combination of your blood pressure, potassium, eGFR, symptoms, and sometimes renin levels ^[11]. Never adjust this medication on your own.
• Be cautious with potassium and other meds: MRAs help your body hold onto potassium. Always ask your doctor before using potassium supplements, salt substitutes (which contain potassium), or over-the-counter painkillers like NSAIDs (ibuprofen, naproxen), which can alter kidney function and dangerously increase potassium levels ^[10].