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GLP-1 and Kidney Disease: FLOW Trial Results and Who Benefits

GLP-1 Companion · 8 min read

Chronic kidney disease (CKD) affects approximately 37 million Americans, and people with type 2 diabetes are at particularly high risk of progressive kidney function loss. Until the FLOW trial reported results in 2024, evidence for GLP-1 medications specifically in CKD was mostly derived from cardiovascular outcome trials, not dedicated kidney trials. The FLOW results changed that — and are reshaping nephrology practice guidelines.

The FLOW Trial: Design and Patient Population

The FLOW trial (Evaluate Renal Function With Semaglutide Once Weekly) was a Phase 3 randomized controlled trial that enrolled 3,533 patients at sites across 28 countries. All participants had type 2 diabetes AND established chronic kidney disease, defined as eGFR between 24 and 75 mL/min/1.73m² (covering moderate to severely impaired kidney function) with elevated urine albumin-creatinine ratio (UACR ≥100 mg/g, indicating significant proteinuria).

Participants were randomized to semaglutide 1.0mg weekly (the standard Ozempic dose) or placebo, on top of standard-of-care treatment, which included background RAAS inhibition (ACE inhibitors or ARBs), and many were also on SGLT2 inhibitors. The trial was designed to run for approximately 3.4 years but was stopped early — in August 2023 — due to overwhelming efficacy at a pre-specified interim analysis.

FLOW Trial Results: Primary and Secondary Outcomes

• Primary composite kidney endpoint (sustained ≥50% eGFR decline, permanent kidney replacement therapy, or kidney-related death): 24% relative risk reduction with semaglutide — hazard ratio 0.76.
• Cardiovascular events (MACE): 18% lower with semaglutide.
• Cardiovascular death: 29% lower with semaglutide.
• All-cause mortality: 20% lower with semaglutide.
• Rate of eGFR decline over time was significantly slower in the semaglutide group.
• UACR (urine albumin-creatinine ratio) was meaningfully reduced with semaglutide, indicating less proteinuria.

Who Specifically Benefits: Critical Context

It is essential to understand the specific population studied in FLOW. These results apply to patients with ALL of the following characteristics: type 2 diabetes, established CKD with eGFR 24–75, and significant proteinuria (UACR ≥100). This is not a general population finding.

The results cannot be extrapolated to patients with CKD due to other causes (lupus nephritis, IgA nephropathy, polycystic kidney disease), non-diabetic CKD without proteinuria, or patients without diabetes using GLP-1 medications for obesity only. Those populations were not studied, and separate trials are needed to determine whether similar benefits apply.

Mechanisms of Kidney Protection

GLP-1 receptor agonists appear to protect the kidneys through multiple complementary pathways, which is one reason why the magnitude of benefit in FLOW was larger than many predicted.

• Improved glycemic control: chronic hyperglycemia is a direct driver of glomerular damage, mesangial expansion, and tubular injury. Better glucose control reduces this damage over time.
• Blood pressure reduction: semaglutide modestly lowers systolic blood pressure (3–6 mmHg), reducing the intraglomerular hypertension that accelerates CKD progression.
• Anti-inflammatory effects: semaglutide reduces systemic inflammatory markers (CRP, IL-6) and local inflammatory signaling within kidney tissue.
• Direct GLP-1 receptor effects on podocytes: podocytes are the specialized filtration cells of the kidney glomerulus. GLP-1 receptors expressed on podocytes may reduce apoptosis and protect filtration function independently of metabolic effects.
• Reduced proteinuria: lower UACR indicates less glomerular leak and reduced kidney injury signaling.
• Weight loss reducing hyperfiltration: excess adiposity causes glomerular hyperfiltration, a precursor to glomerulosclerosis; weight loss normalizes this.

Practical Implications: Updating Nephrology Practice

Prior to FLOW, the cardiorenal protection landscape for T2D + CKD was dominated by SGLT2 inhibitors (empagliflozin, dapagliflozin, canagliflozin), which had demonstrated kidney protection in the CREDENCE and DAPA-CKD trials. The FLOW data positions semaglutide as a second major pillar of kidney protection, potentially complementary to SGLT2 inhibitors.

Nephrology guidelines are being updated to reflect FLOW results. The Kidney Disease: Improving Global Outcomes (KDIGO) guidelines are expected to formally recommend semaglutide as a preferred option in patients with T2D and CKD, particularly in those who cannot use SGLT2 inhibitors or who need additional kidney protection on top of SGLT2 therapy.

The FLOW trial did not just add semaglutide to a list of options. It demonstrated that a GLP-1 receptor agonist can meaningfully slow the inexorable progression of diabetic kidney disease — one of the most common causes of end-stage renal failure worldwide. This is a fundamental advance in nephrology.

Combining GLP-1 Medications With SGLT2 Inhibitors

SGLT2 inhibitors and GLP-1 receptor agonists work through distinct mechanisms. SGLT2 inhibitors primarily protect the kidney through afferent arteriole constriction (reducing intraglomerular pressure), glycosuria, and modest blood pressure lowering. GLP-1 receptor agonists act through the pathways described above. Because these mechanisms are non-overlapping, the two classes can — and arguably should — be used together in high-risk T2D + CKD patients, with appropriate provider oversight.

In FLOW, approximately 16% of participants were already using SGLT2 inhibitors at baseline, and semaglutide produced benefits on top of SGLT2 therapy in this subgroup. This strongly supports the concept of combination cardiorenal protection.

Dosing in Chronic Kidney Disease

One practical advantage of semaglutide in CKD is its dosing flexibility. Unlike metformin (which requires eGFR ≥30 and is generally stopped at eGFR <45 due to lactic acidosis risk) or SGLT2 inhibitors (which lose glycemic efficacy below eGFR 45), semaglutide does not require dose adjustment based on kidney function and can be used at eGFR levels down to approximately 15.

Tirzepatide data in patients with severe CKD (eGFR <30) is more limited — the FLOW-equivalent tirzepatide kidney trials are ongoing. Patients with eGFR below 30 considering tirzepatide should consult both their prescribing physician and a nephrologist.

Monitoring Kidney Health on GLP-1 Therapy

Patients with CKD on GLP-1 medications require systematic monitoring. This is not simply standard GLP-1 monitoring — it requires the more intensive oversight appropriate for CKD management.

• eGFR and UACR: measure at least every 6 months; more frequently (every 3 months) in patients with eGFR below 45 or rapidly changing kidney function.
• Electrolytes (sodium, potassium, bicarbonate): relevant in CKD as GLP-1 medications promote some natriuresis; monitor for electrolyte imbalance.
• Blood pressure: track at every visit; GLP-1-related BP reductions may require antihypertensive dose adjustment in CKD patients.
• Avoid nephrotoxic medications and NSAIDs, which are already contraindicated in CKD and may cause acute kidney injury in combination with volume depletion.
• Report any significant decrease in urine output, swelling, or fatigue to your healthcare provider promptly.

The Bottom Line

The FLOW trial established semaglutide as one of the most effective medications available for slowing kidney disease progression in patients with type 2 diabetes and CKD. The 24% reduction in major kidney events, combined with 20% lower all-cause mortality, makes this a practice-changing result. For patients who fit the FLOW population — T2D, eGFR 24–75, UACR ≥100 — semaglutide should be a strong consideration as part of comprehensive cardiorenal risk reduction, alongside SGLT2 inhibitors and RAAS blockade.

Sources

• Perkovic et al. (2024). Semaglutide and Kidney Outcomes in Type 2 Diabetes. NEJM.
• Drucker DJ (2018). Mechanisms of Action and Therapeutic Application of GLP-1. Cell Metabolism.