Chronic Kidney Disease (CKD)/ ACR

What is Chronic Kidney Disease (CKD)?

CKD is defined as abnormalities in kidney structure or function (eGFR < 60 ml/min/1.73m² or evidence of kidney damage such as proteinuria) persisting for > 3 months.

Common Causes

  • Diabetes mellitus (most common in UK)
  • Hypertension
  • Glomerulonephritis
  • Polycystic kidney disease
  • Obstructive uropathy (e.g. BPH, stones)
  • Recurrent urinary tract infections
  • Medications (e.g. NSAIDs, lithium)

Stepwise Clinical Approach

Step 1: Confirm CKD

  • eGFR < 60 ml/min/1.73m² on at least 2 occasions, 3 months apart
  • or proteinuria/haematuria, structural abnormalities or biopsy-proven kidney disease persisting > 3 months

Step 2: Classify Stage of CKD

  • G1: eGFR ≥ 90 with other markers of damage
  • G2: eGFR 60-89 with other markers of damage
  • G3a: eGFR 45-59
  • G3b: eGFR 30-44
  • G4: eGFR 15-29
  • G5: eGFR < 15 (end-stage renal disease)

Also classify albuminuria: A1 (< 3 mg/mmol), A2 (3-30), A3 (> 30)

Step 3: Initial Investigations

  • Urine ACR (Albumin:Creatinine Ratio)
  • Urine dipstick - check for haematuria
  • U&Es, eGFR, FBC, glucose or HbA1c, calcium, phosphate, PTH, vitamin D
  • Renal ultrasound - if eGFR < 45 or suspicion of obstruction or polycystic kidney disease
  • BP measurement - check for hypertension control

Step 4: Management Principles

  • Control BP – aim < 140/90 mmHg, or < 130/80 if ACR > 30
  • ACEi or ARB if diabetic nephropathy or ACR > 3
  • Glycaemic control in diabetics (HbA1c ~ 48-58 mmol/mol)
  • Dietary advice - low phosphate and salt
  • Statin therapy (QRISK2 ≥ 10%)
  • Avoid nephrotoxic medications (NSAIDs)

Step 5: Monitoring and Follow-up

  • Stable CKD G3a without ACR: repeat U&Es annually
  • With ACR or progression risk: monitor every 3 - 6 months
  • Monitor potassium and bicarbonate (metabolic acidosis is common)

Step 6: When to Refer to Nephrology

  • eGFR < 30 ml/min/1.73m² (G4-G5)
  • ACR ≥ 70 mg/mmol, unless diabetic and already appropriately treated
  • Persistent haematuria with proteinuria or abnormal imaging
  • Unexplained decline in eGFR > 5 ml/min in 1 year or > 10 over 5 years
  • Suspected secondary cause (e.g. glomerulonephritis)
  • Resistant hypertension despite 4+ medications

What is ACR?

Albumin:creatinine ratio (ACR) detects and quantifies protein (albumin) loss in urine. It is a key test in diagnosing and monitoring CKD, especially in people with diabetes or hypertension.

Reference Ranges (Spot Urine Sample)

  • < 3 mg/mmol: no action needed
  • 3 - 70 mg/mmol: repeat ACR within 3 months
  • > 70 mg/mmol: indicates significant proteinuria - no repeat needed, proceed with CKD workup

Stepwise Clinical Approach

Step 1: First Sample

Request early morning urine ACR sample. Avoid samples during menstruation or UTI.

Step 2: If ACR ≥ 3 mg/mmol

  • Repeat 2 additional early morning samples within 3 months
  • Diagnosis of proteinuria confirmed if 2 out of 3 ACR results ≥ 3 mg/mmol
  • Use PCR (protein:creatinine ratio) if ACR > 70 mg/mmol or to monitor treatment

Step 3: Rule Out Transient Causes

  • Exclude UTI (send MSU if dipstick positive)
  • Post-exercise, fever, or upright posture may temporarily raise ACR

Step 4: Check for CKD

  • Repeat eGFR and ACR 3 months apart
  • CKD is diagnosed if ACR ≥ 3 mg/mmol or eGFR < 60 for > 3 months
  • Classify CKD based on ACR and eGFR together

Step 5: Additional Investigations

  • BP, HbA1c, lipid profile, BMI, and dipstick for haematuria
  • Renal ultrasound if: structural abnormalities suspected, family history of polycystic kidney disease, or aged > 20

Step 6: When to Refer to Nephrology

  • ACR persistently > 70 mg/mmol (even with normal eGFR)
  • ACR 30 - 70 mg/mmol with haematuria or reduced eGFR
  • Progressive decline in eGFR or uncontrolled hypertension
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