Diagnosis

• based on clinical features - uraemia should be considered in any patient who is nonspecifically unwell and where the diagnosis is uncertain.
• dipstick urinanalysis - proteinuria and microscopic haematuria are suggestive of renal parenchymal disease (glomerulonephritis).
• MSU - if red cell casts are seen then this supports a possible diagnosis of renal parenchymal disease.
• serum urea, creatinine and electrolytes - serum creatinine is a better guide to renal function than urea which may be disproportionately elevated e.g. by dehydration, gastrointestinal haemorrhage. Hyperkalaemia may be present.

Definition of AKI

Acute kidney injury is defined when one of the following criteria is met

• serum creatinine rises by >= 26 µmol/L within 48 hours or
  
  
• serum creatinine rises >= 1.5 fold from the reference value, which is known or presumed to have occurred within one week or
  
  
• oliguria (urine output is < 0.5ml/kg/hr for >6 consecutive hours) or
  
  
• a 25% or greater fall in eGFR in children and young people within the past 7 days (3)

The reference serum creatinine should be the lowest creatinine value recorded within 3 months of the event

If a reference serum creatinine value is not available within 3 months and AKI is suspected

• repeat serum creatinine within 24 hours
• a reference serum creatinine value can be estimated from the nadir serum creatinine value if patient recovers from AKI

Staging of AKI

• formula-based estimated GFR should be interpreted with caution in AKI - this is because the formulae rely on a stable serum creatinine concentration
• is a clinical syndrome characterised by a rapid decline in excretory function occurring over a period of hours or day
• if a patient has suspected AKI the s/he should be referred to a nephrologist
• acute on chronic renal failure
  • if there has been a fall in estimated GFR of >25% since the last measurement of kidney function in a patient with CKD should prompt a repeat measurement of kidney function, assessment as for AKI and referral if the deterioration is confirmed

Reference:

1. The Renal Association (May 2006).UK CKD Guidelines
2. UK Renal Association (2011). Acute Kidney Injury
3. NICE (August 2013). Acute kidney injury - Prevention, detection and management of acute kidney injury up to the point of renal replacement therapy