Urea and Creatinine/AKI

What Are Urea and Creatinine?

Urea and creatinine are waste products excreted by the kidneys. They help assess renal function, hydration status, and detect acute or chronic kidney injury. Creatinine is more reliable for estimating renal function (eGFR).

Reference Ranges

  • Urea: 2.5 - 7.8 mmol/L
  • Creatinine: 60 - 120 µmol/L (may vary with muscle mass and sex)

Stepwise Clinical Approach

Step 1: Confirm and Repeat

Repeat urea and creatinine to confirm abnormal results, ideally alongside eGFR, FBC, and electrolytes. Rule out transient factors such as dehydration or recent ACEi/NSAID use.

Step 2: Interpret Elevations

  • Isolated high urea: may suggest dehydration, GI bleed, or high protein intake
  • High urea and creatinine: may indicate AKI or CKD – assess with eGFR and baseline creatinine
  • Urea:creatinine ratio > 100:1: likely prerenal (dehydration, heart failure, GI bleed)

Step 3: Assess Chronicity

  • Check previous renal profiles – chronic elevation suggests CKD
  • If new or worsening, follow AKI protocol and assess for triggers (e.g. sepsis, medication)

Step 4: Check for Symptoms

  • Nausea, vomiting, fatigue, confusion, or reduced urine output may suggest uraemia
  • Assess for signs of fluid overload or hypovolaemia

Step 5: Escalate If Needed

  • Rapidly rising creatinine or eGFR drop ≥ 25%: urgent senior review or admission
  • Severe electrolyte disturbance or uraemia symptoms: consider same-day nephrology input
  • eGFR < 30 or creatinine > 200 µmol/L unexplained: refer to renal team

What is Acute Kidney Injury (AKI)?

AKI is a sudden drop in kidney function. It can happen over hours or days and is often picked up through rising creatinine or reduced urine output.

Diagnosis: based on either:

  • ↑ Creatinine by 26 µmol/L in 48 hrs
  • ↑ Creatinine to 1.5x baseline within 7 days
  • Urine output < 0.5 mL/kg/hr for 6 hrs

Common Causes of AKI

1. Pre-renal (not enough blood to kidneys)

  • Examples: dehydration, diarrhoea, sepsis, heart failure
  • Clue: low BP, dry mouth, ↓ urine output

2. Renal (damage within the kidney)

  • Examples: acute tubular necrosis (ATN), glomerulonephritis, nephrotoxins (e.g. NSAIDs, contrast)
  • Clue: protein/blood in urine, recent contrast or medication change

3. Post-renal (blocked drainage)

  • Examples: prostate enlargement, stones, catheter blockage
  • Clue: difficulty passing urine, palpable bladder

Stepwise Management

Step 1: Check U&Es and urine output

Compare to previous creatinine. Check if urine output < 500 mL in 24 hrs.

Step 2: Stop harmful drugs

  • Hold ACE inhibitors, NSAIDs, diuretics, metformin

Step 3: Assess volume status

  • Dry? → give fluids (e.g. IV 500 mL NaCl)
  • Overloaded? → consider furosemide or call for help

Step 4: Check potassium and refer if needed

  • Urgent if K+ > 6.5 or ECG changes
  • Refer if stage 3 AKI or unclear cause

When to refer urgently

  • Creatinine rising fast or > 354 µmol/L
  • No urine output for > 12 hrs
  • K+ > 6.5 mmol/L
  • Suspected glomerulonephritis

→ Contact on-call renal or acute medical team

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