What Are the Kidneys and What Can Go Wrong?
The kidneys — two fist-sized organs sitting below the rib cage — filter approximately 180 litres of blood daily, excreting waste products in urine, regulating blood pressure via the renin-angiotensin system, controlling fluid and electrolyte balance, activating vitamin D, and stimulating red blood cell production (erythropoietin). Chronic kidney disease (CKD) is a sustained reduction in kidney function or structural damage lasting more than three months.
CKD affects approximately 850 million people worldwide — about 1 in 10 adults. It is a major cause of cardiovascular disease and premature death, and is the 12th leading cause of global mortality.
The Five Stages of CKD
CKD is staged by estimated glomerular filtration rate (eGFR), which estimates how much blood the kidneys filter per minute per 1.73 m² body surface area:
- Stage 1 — eGFR ≥90: Kidney damage (e.g. proteinuria) with normal or high function. Often no symptoms.
- Stage 2 — eGFR 60–89: Mildly reduced function. Usually asymptomatic.
- Stage 3a/3b — eGFR 30–59: Moderately reduced function. Fatigue, anaemia, and fluid retention may begin. Blood pressure often rises.
- Stage 4 — eGFR 15–29: Severely reduced function. Symptoms more prominent. Dialysis planning begins.
- Stage 5 — eGFR <15: Kidney failure. Dialysis or transplantation required to sustain life.
Proteinuria: The Other Key Marker
Protein in the urine (proteinuria or albuminuria) is an independent marker of CKD severity and cardiovascular risk. The urine albumin-to-creatinine ratio (uACR) classifies kidney damage:
- Normal: <3 mg/mmol
- Moderately increased (A2): 3–30 mg/mmol
- Severely increased (A3): >30 mg/mmol
Both eGFR and albuminuria together determine prognosis more accurately than either alone.
What Causes CKD?
- Diabetes — diabetic nephropathy is the leading cause globally, accounting for ~30–40% of cases
- Hypertension — the second most common cause; high pressure damages glomerular capillaries
- Glomerulonephritis — immune-mediated inflammation of the filtering units
- Polycystic kidney disease — genetic disorder causing progressive cyst growth
- Obstructive uropathy — chronic urinary tract obstruction (e.g. enlarged prostate, kidney stones)
- NSAIDs and nephrotoxic medications — chronic analgesic use is an underappreciated cause
- Recurrent kidney infections
Early Warning Signs
CKD is often called a "silent disease" because it produces no symptoms until Stage 3–4. When present, symptoms include:
- Persistent fatigue and weakness (anaemia of CKD)
- Foamy or frothy urine (sign of proteinuria)
- Blood in urine (haematuria)
- Swelling in ankles, feet, or around the eyes (fluid retention)
- Reduced urine output or conversely needing to urinate at night
- Loss of appetite, nausea, vomiting (uraemia — toxin accumulation)
- Dry, itchy skin
- Difficulty concentrating
- High blood pressure that is difficult to control
Treatment and Slowing Progression
Blood Pressure Control
Target <130/80 mmHg. ACE inhibitors or ARBs are first-line in CKD — beyond blood pressure lowering, they reduce glomerular pressure and proteinuria directly, slowing CKD progression regardless of diabetes status.
SGLT2 Inhibitors (Game-Changer)
Dapagliflozin and canagliflozin are now recommended for CKD patients with proteinuria, regardless of diabetes status (DAPA-CKD and CREDENCE trials). They reduce the risk of kidney failure by 30–40% and cardiovascular events simultaneously.
Finerenone
A non-steroidal mineralocorticoid receptor antagonist approved for CKD in type 2 diabetes. Reduces CKD progression and cardiovascular events beyond RAS blockade alone.
Glycaemic Control in Diabetes
HbA1c target of approximately 7% (53 mmol/mol) in diabetic CKD reduces proteinuria progression. Metformin requires dose adjustment (eGFR <30: contraindicated). Insulin remains safe at all stages.
Dietary Management
- Protein: Low-protein diet (0.6–0.8 g/kg/day) in non-dialysis CKD may slow progression; excessive protein increases urea burden
- Salt: Limit to <5 g/day (sodium <2 g/day) for blood pressure control and to reduce proteinuria
- Potassium: Restriction needed in later stages (CKD 4–5) when hyperkalaemia risk rises
- Phosphate: Restrict processed foods high in phosphate additives; phosphate binders prescribed in advanced CKD
Anaemia Management
Erythropoiesis-stimulating agents (ESAs) and oral iron (or IV iron when oral is insufficient) treat CKD anaemia. Target haemoglobin 100–120 g/L — over-correction increases cardiovascular risk.