Chronic Kidney Disease and Diabetes: The Silent Connection

Chronic kidney disease (CKD) and Type 2 diabetes are so frequently intertwined that the medical community has coined a specific term for their convergence — diabetic kidney disease (DKD). It affects approximately 40% of people with Type 2 diabetes and is the leading cause of end-stage renal disease (ESRD) requiring dialysis in most developed countries.^[1] Yet most patients with early DKD have no symptoms whatsoever. The kidneys can lose 50–60% of their function before any clinical warning sign appears.

How Hyperglycaemia Damages the Kidneys

The glomerulus — the kidney’s filtering unit — is a delicate structure of specialised cells including podocytes, endothelial cells, and mesangial cells. Chronic hyperglycaemia damages each of these cell types through multiple converging mechanisms:^[2]

• Advanced glycation end-products (AGEs): Glucose reacts with proteins throughout the body to form AGEs, which activate specific receptors (RAGE) on glomerular cells, triggering oxidative stress and pro-inflammatory gene expression.
• Haemodynamic injury: Hyperglycaemia causes preferential dilation of the afferent arteriole while the efferent arteriole remains constricted, increasing intraglomerular pressure. This mechanical stress directly damages the filtration barrier and drives proteinuria.
• Podocyte injury and loss: Podocytes are the gatekeepers of glomerular filtration. They are terminally differentiated and cannot regenerate. Diabetes-induced oxidative stress and mechanical stress cause podocyte apoptosis; as podocytes are lost, proteinuria increases and glomerulosclerosis progresses.
• Tubulointerstitial fibrosis: Activation of TGF-β1 promotes mesangial expansion and tubulointerstitial fibrosis — the structural change that permanently reduces GFR.

The Critical Role of Albuminuria: The UACR Test

The earliest detectable sign of diabetic kidney disease is microalbuminuria — the leakage of small amounts of albumin into the urine. This is detected by the urine albumin-to-creatinine ratio (UACR), a simple morning urine test.^[3]

• Normal: UACR below 3 mg/mmol (below 30 mg/g)
• Microalbuminuria (A2): 3–30 mg/mmol (30–300 mg/g) — early DKD, high reversibility with intervention
• Macroalbuminuria (A3): Above 30 mg/mmol (above 300 mg/g) — established DKD, progressive without treatment

Current guidelines recommend annual UACR testing for all patients with Type 2 diabetes, beginning at diagnosis (unlike Type 1, where screening begins 5 years post-diagnosis).^[4] The window of opportunity for intervention is widest at the microalbuminuria stage — regression to normal is achievable in up to 30% of patients with optimal metabolic control.

eGFR: Staging Kidney Disease

Estimated glomerular filtration rate (eGFR) quantifies how well the kidneys are filtering. CKD staging by eGFR (the CGA classification of KDIGO 2022):^[5]

• G1: eGFR ≥90 (normal or high) – diagnosis requires albuminuria or structural abnormality
• G2: eGFR 60–89 (mildly decreased)
• G3a: eGFR 45–59 (mild-moderately decreased)
• G3b: eGFR 30–44 (moderate-severely decreased)
• G4: eGFR 15–29 (severely decreased) – nephrology referral essential
• G5: eGFR below 15 – kidney failure, dialysis or transplant planning

The Therapeutic Revolution: SGLT2 Inhibitors and Finerenone

The past decade has produced the most significant advances in DKD treatment in 30 years, centred on two drug classes:

SGLT2 inhibitors (empagliflozin, dapagliflozin, canagliflozin) reduce intraglomerular pressure by increasing natriuresis and reducing afferent arteriole tone — a mechanism entirely distinct from their glucose-lowering effect. The EMPA-KIDNEY trial (empagliflozin) showed a 28% relative risk reduction in CKD progression or cardiovascular death in patients with CKD regardless of diabetes status.^[6] The DAPA-CKD trial (dapagliflozin) demonstrated a 39% reduction in the composite of eGFR decline ≥50%, ESRD, renal or cardiovascular death.^[7]

Finerenone, a non-steroidal mineralocorticoid receptor antagonist, has demonstrated additive kidney protection on top of ACE inhibitor/ARB therapy in the FIDELIO-DKD and FIGARO-DKD trials, reducing proteinuria and slowing eGFR decline.^[8] It is now recommended in major guidelines as add-on therapy for DKD at UACR above 30 mg/mmol.

Blood Pressure and RAS Blockade: The Cornerstone

Renin-angiotensin system (RAS) blockade with ACE inhibitors (ramipril, enalapril) or ARBs (losartan, irbesartan) remains the cornerstone of DKD treatment. They reduce intraglomerular pressure by dilating the efferent arteriole, reduce proteinuria by 35–40%, and slow eGFR decline independently of blood pressure effects.^[9] Target blood pressure in DKD is below 130/80 mmHg, and below 120/80 in those with significant proteinuria.

Dietary Management in CKD and Diabetes

Nutrition management in DKD requires balancing multiple competing concerns:^[10]

• Protein: Moderate protein restriction (0.8g/kg/day) slows GFR decline in advanced CKD (G4–G5). In earlier stages, restriction is not necessary but excessive protein (>1.5g/kg/day) should be avoided.
• Potassium: Hyperkalaemia risk rises with declining eGFR; potassium-rich foods (bananas, potatoes, tomatoes, legumes) require monitoring when eGFR falls below 30.
• Phosphate: Phosphate retention contributes to renal osteodystrophy and cardiovascular calcification; processed foods with phosphate additives should be minimised.
• Sodium: Restricting sodium to below 2,000 mg/day reduces blood pressure and proteinuria.