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 decline in kidney function over hours to days.

• Creatinine rise ≥ 26 µmol/L within 48 hours
• Creatinine ≥ 1.5 × baseline within 7 days
• Urine output < 0.5 mL/kg/hour for 6 hours

Important: eGFR will drop as creatinine rises, but AKI staging is based on creatinine change.

AKI Staging (Creatinine-Based)

• Stage 1: 1.5-1.9 × baseline
• Stage 2: 2.0-2.9 × baseline
• Stage 3: ≥ 3 × baseline OR creatinine ≥ 354 µmol/L

Primary Care Management Based on Severity

AKI Stage 1 (e.g. eGFR drop from 65 → 45)

• Patient clinically well
• Stop nephrotoxic drugs (ACEi, ARB, NSAIDs, diuretics if dehydrated, metformin)
• Assess hydration and encourage oral fluids if dry
• Ensure potassium result reviewed urgently
• Repeat U&Es within 48-72 hours (or within 1 week if stable)
• Escalate if worsening or symptomatic

AKI Stage 2 (e.g. eGFR drop from 65 → 30)

• Urgent GP/clinician review
• Stop nephrotoxic drugs immediately
• Ensure potassium level known same day (if not possible refer to a/e)
• Assess for dehydration or fluid overload
• Low threshold for referral to A&E, especially if elderly, frail or comorbid CKD

AKI Stage 3 (e.g. eGFR drop from 60 → 15) OR:

• Creatinine ≥ 354 µmol/L
• Potassium ≥ 6.0 mmol/L
• No urine output
• Suspected obstruction
• Clinically unwell or septic

→ Urgent GP review with immediate referral to A&E

Example – Primary Care

• Baseline eGFR 70
• Current eGFR 42
• Creatinine risen from 90 → 140
• Recent diarrhoea

Likely Stage 1 AKI (pre-renal)

• Stop ramipril temporarily
• Encourage fluids
• Repeat U&Es in 2-3 days (or withn 1 week if stable)
• Escalate if worsening

Secondary Care Management

Monitoring

• Strict fluid balance
• Urine output hourly
• Daily or more frequent U&Es

IV Fluids

• 0.9% sodium chloride if hypovolaemic
• Avoid overload in heart failure

Complications

• Hyperkalaemia protocol if needed
• Treat acidosis
• Dialysis if refractory hyperkalaemia, severe acidosis, fluid overload, or uraemia

Example – Secondary Care

• Baseline eGFR 60
• Now eGFR 18
• Creatinine 380 µmol/L
• Potassium 6.3 mmol/L
• Reduced urine output

Stage 3 AKI with hyperkalaemia

• Continuous cardiac monitoring
• IV calcium gluconate
• Insulin + glucose
• IV fluids if hypovolaemic
• Renal team review

Example 1: AKI in Primary Care

Scenario
78 year old with diarrhoea for 3 days. On ramipril and furosemide. Blood test shows creatinine increased from 95 to 145 µmol/L.

What this likely is

• Pre-renal AKI from dehydration
• Worsened by ACE inhibitor and diuretic
• Likely AKI Stage 1

What to do in Primary Care

• Stop ramipril and furosemide temporarily
• Advise good oral fluids (if able)
• Check potassium urgently
• Repeat U&Es in 24-48 hours (if possible)
• Give clear safety advice: if confusion, reduced urine, or worsening symptoms → attend hospital

When to escalate

• If potassium ≥ 6.0 mmol/L
• If creatinine continues rising
• If unable to maintain hydration
• If patient clinically unwell

Example 2: AKI in Hospital

Scenario
70 year old admitted with sepsis. Creatinine rose from 100 to 320 µmol/L in 48 hours. Urine output very low. Potassium 6.4 mmol/L.

What this likely is

• AKI Stage 3
• Likely acute tubular necrosis from sepsis
• Life-threatening hyperkalaemia

Immediate Hospital Management

• Cardiac monitoring
• IV calcium gluconate for cardiac protection
• IV insulin and glucose for hyperkalaemia
• IV fluids (if not fluid overloaded)
• Treat sepsis with IV antibiotics
• Strict fluid balance monitoring

Next Steps

• Daily blood tests
• Renal team involvement
• Consider dialysis if potassium remains high, severe acidosis, or fluid overload