Chronic Kidney Disease

Chronic kidney disease (CKD) is a long-term condition in which the kidneys lose their ability to filter blood effectively, accumulate wastes, and maintain the body's internal balance. It affects approximately 10% of the global adult population -- and in Singapore, where diabetes and hypertension are prevalent, CKD is both extremely common and frequently underdiagnosed until an advanced stage.

What makes CKD particularly challenging is its silence. In the early and middle stages, CKD causes no symptoms. Patients with Stage 1-3 CKD may feel entirely well while their kidneys are quietly losing function. By the time symptoms appear, kidney damage is often significant. This is why knowing your eGFR and urine albumin -- the two numbers that define CKD -- is critical for anyone with diabetes, hypertension, or a family history of kidney disease.

What do Kidneys Do?

The kidneys are a pair of bean-shaped organs, each about the size of a fist, located at the back of the abdominal cavity. Despite their modest size, they perform functions that are essential for life:

• Filtration: The kidneys filter the blood to remove waste products, extra salts, and excess water, which are excreted as urine.
• Fluid and electrolyte balance: The kidneys regulate the body's sodium, potassium, calcium, phosphate, and acid-base balance with extraordinary precision.
• Blood pressure regulation: The renin-angiotensin-aldosterone system (RAAS), centred in the kidneys, is the primary long-term regulator of blood pressure.
• Hormone production: The kidneys produce erythropoietin (which stimulates red blood cell production), activate vitamin D (essential for bone health), and produce renin (blood pressure regulation).

Chronic Kidney Disease (CKD) is the gradual loss of kidney function over time. This increases your risk of developing other health problems such as heart disease and stroke. Over time, if left untreated, CKD can lead to kidney failure, also known as end-stage kidney disease. There is no cure for CKD but there are steps you can take to slow down the progression of kidney damage. 

When CKD develops, all these functions progressively fail, producing the wide range of complications that characterise advanced kidney disease.

How Chronic Kidney Disease is Defined: eGFR and Albuminuria

CKD is defined by the international KDIGO (Kidney Disease: Improving Global Outcomes) guidelines as the presence of either a reduced eGFR or markers of kidney damage (particularly albuminuria) for three months or more. Both dimensions matter -- and using both together gives a more accurate picture of CKD severity than either alone.

Estimated Glomerular Filtration Rate (eGFR)

The eGFR is calculated from a blood creatinine measurement (along with age, sex, and in some formulae, race) and estimates how many millilitres of blood the kidneys filter per minute, corrected for body surface area. The CKD-EPI formula (Chronic Kidney Disease Epidemiology Collaboration) is the current recommended formula.

• Normal eGFR: above 90 ml/min/1.73m²
• CKD is defined by eGFR persistently below 60 ml/min/1.73m² -- confirmed on at least two measurements at least 3 months apart
• eGFR naturally declines with age (approximately 1 ml/min/year from the 40s), so a single mildly reduced eGFR in an older patient requires careful interpretation

Urine Albumin-to-Creatinine Ratio (ACR)

Albuminuria -- the presence of albumin (a protein) in the urine -- is a sensitive marker of kidney damage and a powerful predictor of both CKD progression and cardiovascular risk. The urine ACR is measured from a spot urine sample:

• A1 (Normal to mildly increased): below 30 mg/g
• A2 (Moderately increased): 30-300 mg/g -- clinical proteinuria
• A3 (Severely increased): above 300 mg/g -- significant proteinuria; high progression risk

A patient with a normal eGFR (above 60) but significant albuminuria (A2 or A3) still has CKD by definition. This is clinically important: early diabetic nephropathy often presents with proteinuria before eGFR begins to fall, and treating proteinuria at this stage is the most effective way to prevent progressive kidney damage.

Causes of Chronic Kidney Disease

Most Common Causes (>80% of CKD in Singapore)

• Diabetic nephropathy: Long-term high blood sugar damages the kidney filters, causing protein to leak into the urine and kidney function to gradually decline. It is the leading cause of kidney failure in Singapore.
• Hypertensive nephrosclerosis: Long-term high blood pressure damages the small blood vessels in the kidneys, leading to scarring and reduced kidney function.

Other important causes

• Glomerulonephritis: Inflammation of the kidney filters caused by the immune system. It often presents with blood and protein in the urine and may require a kidney biopsy for diagnosis.
• Polycystic kidney disease (PKD): An inherited condition in which multiple fluid-filled cysts gradually replace normal kidney tissue, leading to loss of kidney function.
• Obstructive uropathy: Long-term blockage of urine flow, such as from an enlarged prostate, kidney stones, or narrowing of the urinary tract, can damage the kidneys if not treated.
• Renovascular disease: Narrowing of the arteries supplying the kidneys reduces blood flow, leading to high blood pressure and kidney damage.
• Recurrent urinary tract infections (UTIs) and reflux nephropathy: Repeated kidney infections or urine flowing backward from the bladder into the kidneys can cause permanent kidney scarring.

Symptoms of CKD

CKD is largely asymptomatic until Stage 3b-4, when enough nephrons have been lost that the compensatory capacity of the remaining kidney is exceeded. This is why so many patients are surprised by a CKD diagnosis -- they felt completely well.

Early Stages: Usually no symptoms

Most patients with early CKD have no symptoms. CKD at this stage is identified on routine blood tests (elevated creatinine, low eGFR) or urine tests (proteinuria, haematuria) performed for screening or for another condition. Hypertension that is resistant to treatment may be a clue.

Later Stages: Symptoms begin

• Fatigue and reduced stamina: One of the earliest and most prominent symptoms; caused by anaemia, metabolic acidosis, and uraemic toxin accumulation
• Reduced urine output, nocturia, or changes in urine colour or foaminess
• Ankle and lower leg swelling (peripheral oedema) from fluid and sodium retention
• Breathlessness, from fluid overload or anaemia
• Poor appetite, nausea, and unintentional weight loss
• Muscle cramps, particularly at night, from electrolyte imbalances
• Difficulty concentrating and cognitive slowing

End-stage: uraemic symptoms

• Severe nausea and vomiting
• Markedly reduced or absent urine output
• Altered consciousness, confusion (uraemic encephalopathy in untreated cases)
• Pericarditis (inflammation of the pericardium from uraemic toxin accumulation)
• Severe fluid overload causing pulmonary oedema

Complications of CKD Beyond the Kidneys

CKD causes a cascade of systemic complications that affect multiple organ systems. Managing these complications alongside the kidney disease itself is a major focus of nephrology care.

• Cardiovascular disease: CKD greatly increases the risk of heart disease. Reduced kidney function can lead to inflammation, high blood pressure, fluid overload, and anaemia, all of which increase the risk of heart attacks, heart failure, and stroke.
• Renal anaemia: Damaged kidneys produce less erythropoietin, resulting in fewer red blood cells. This can cause tiredness, shortness of breath, and reduced exercise tolerance. Treatment includes iron supplements and medications that stimulate red blood cell production.
• CKD mineral and bone disease: Poor kidney function causes phosphate to build up and reduces vitamin D activation, leading to weak bones and calcium deposits in blood vessels. Treatment includes limiting dietary phosphate, phosphate binders, and vitamin D supplements.
• Hyperkalaemia: Reduced kidney function can cause high potassium levels in the blood, increasing the risk of dangerous heart rhythm problems. It is managed with diet, medication adjustments, and potassium-lowering treatments.
• Metabolic acidosis: The kidneys become less able to maintain the body's acid balance, leading to excess acid in the blood. This can weaken muscles, damage bones, and worsen kidney disease. It is treated with sodium bicarbonate.
• Fluid overload and hypertension: The kidneys cannot remove enough salt and water, causing swelling, high blood pressure, and sometimes fluid in the lungs. Treatment includes reducing salt intake, using diuretics, and controlling blood pressure.

Diet and Lifestyle in CKD

Diet is a powerful tool in CKD management. As kidney function declines, dietary modification becomes increasingly important -- but the specific restrictions differ by stage, making dietitian involvement essential.

• Sodium (salt): Limit salt intake to less than 5 g per day to help control blood pressure, reduce swelling, and protect the kidneys. Processed foods are a major source of hidden salt.
• Potassium: If blood potassium levels become high (usually in later-stage CKD), limit high-potassium foods such as bananas, oranges, tomatoes, potatoes, leafy greens, and coconut water. Boiling vegetables can help reduce their potassium content.
• Phosphate: In later-stage CKD, limit foods high in phosphate, including dairy products, nuts, seeds, whole grains, dark cola drinks, and processed foods.
• Protein: Moderate protein intake is recommended in advanced CKD before dialysis to reduce strain on the kidneys. Patients on dialysis need more protein to replace protein lost during treatment.
• Fluid: Fluid restriction is usually unnecessary in early CKD but may be needed in advanced CKD if swelling, high blood pressure, or reduced urine output develops.

How Chronic Kidney Disease is Diagnosed

CKD diagnosis requires two abnormal tests at least three months apart -- confirming the chronic nature of the impairment and distinguishing CKD from acute kidney injury. The diagnostic workup also aims to identify the underlying cause, which determines specific treatment.