Acute Kidney Injury
Also written as AKI.
The most common type of acute kidney injury in the inpatient setting is:
ACUTE KIDNEY INJURY (AKI)
- Definition: A rapid decline in kidney function, defined by any of the following criteria within 48 hours: - Increase in serum creatinine by ≥26.5 μmol/L. - Increase in serum creatinine to ≥1.5 times baseline. - Urine output <0.5 mL/kg/hr fo
- Prerenal AKI: Caused by decreased renal perfusion. Common causes include hypovolaemia, heart failure, sepsis, NSAIDs, and ACE inhibitors. Characterised by FENa <1%, urine sodium <20 mEq/L, specific gravity 1.020, and hyaline casts. It typic
- Intrinsic AKI: Damage to the kidney parenchyma. - ATN (Acute Tubular Necrosis): The most common cause of intrinsic AKI. Can be ischaemic or nephrotoxic (e.g., from aminoglycosides, contrast dye, myoglobin). Characterised by FENa 2% and mudd
- Postrenal AKI: Caused by obstruction of the urinary tract. Common causes include benign prostatic hyperplasia (BPH), kidney stones, and malignancy. Hydronephrosis may be seen on ultrasound.
- Complications of AKI: Hyperkalaemia (the most dangerous), metabolic acidosis, fluid overload, and uraemia.
Read this in Endocrine & Renal Pathology — Must Know Notes
ACUTE KIDNEY INJURY (AKI)
- Definition (KDIGO): Creatinine ↑ ≥26.5 μmol/L in 48h OR ≥1.5× baseline in 7 days OR urine output <0.5 mL/kg/hr for 6h.
- Prerenal causes: Hypovolaemia, heart failure, sepsis, NSAIDs (afferent arteriole constriction), ACEi/ARBs (efferent arteriole dilation).
- ATN causes: Prolonged ischaemia, aminoglycosides, contrast media, myoglobin (rhabdomyolysis), haemoglobin.
- AIN: Drug hypersensitivity (NSAIDs, penicillins, sulfonamides). Classic triad: fever + rash + eosinophilia. WBC casts + eosinophils in urine.
- Postrenal: BPH, stones, malignancy → hydronephrosis on USS.
Read this in Endocrine & Renal Pathology
What our notes say
- The most common type of acute kidney injury in the inpatient setting is: (Internal Medicine (MBIM 4100) special/supplementary exam, Paper Two: 14 August 2)
- The following is true regarding acute kidney injury in children: (Paediatrics end of fourth year main exam: 1 July 2019, Paper One, 99 of 100 MCQs)
- Acute kidney injury is a sudden fall in kidney function over hours to days, with a rise in serum creatinine and a build-up of urea, water, potassium and acids. (Paediatrics end of fourth year main exam: 1 July 2019, Paper One, 99 of 100 MCQs)
- Cerebral malaria with convulsions and coma, pulmonary oedema and acute respiratory distress, acute kidney injury, jaundice, and maternal death. (Junior Clerkship in Reproductive Health (MBOG 4200): end of year examination, 4 )
- Hypovolaemia and acute kidney injury, and loss of binding proteins causing low calcium and thyroxine-binding changes. (Paediatrics and Child Health end of semester examination (MBPE): 10 January 2023)
- Topics tested: anaemias, iron studies, haemolysis, bleeding disorders, haemochromatosis, acute kidney injury, glomerular and tubulointerstitial disease, kidney stones, dialysis and chronic kidney disease staging. (Internal Medicine End of Semester CAT (MBChB 4): haematology and renal, 30 MCQs )
Study material on Acute Kidney Injury
- Acute kidney injury
- Endocrine & Renal Pathology — Must Know Notes
- Endocrine & Renal Pathology
- Internal Medicine End of Semester CAT (MBChB 4): haematology and renal, 30 MCQs and 3 short answers
- Paediatrics end of fourth year main exam: 1 July 2019, Paper One, 99 of 100 MCQs and essays
- Internal Medicine (MBIM 4100) special/supplementary exam, Paper Two: 14 August 2019
- Renal, Liver, Cardiac & Adrenal Function Tests for Year 3
- Internal Medicine (MBIM 4100) main exam, Paper One: 3 July 2019
- Chemical Path Mcqs
- Chemical Pathology
- CHEMICAL PATHOLOGY MCQs
Practice questions on Acute Kidney Injury
In acute kidney injury (AKI), which finding is MOST indicative of a prerenal cause?
- Urine Na <20 mmol/L, high fractional excretion of urea (FeUrea)
- Urine Na >40 mmol/L, low fractional excretion of urea (FeUrea)
- Urine Na <20 mmol/L, low fractional excretion of urea (FeUrea) ✓
- Urine Na >40 mmol/L, high fractional excretion of urea (FeUrea)
Answer: C. In prerenal AKI, the kidneys attempt to conserve sodium and water. Thus, urine sodium is typically low (<20 mmol/L), and the fractional excretion of urea (FeUrea) is also low (<35%) as the kidneys reabsorb urea along with water. In intrinsic renal disease, tubular function is impaired, leading to higher urine sodium and FeUrea. ---
Which of the following is most indicative of acute kidney injury (AKI)?
- Stable creatinine of 1.2 mg/dL
- Gradual increase in GFR over months
- Rapid decline in GFR, leading to accumulation of nitrogenous waste (e.g., sudden increase in creatinine by >0.3 mg/dL or 50%…
- Persistent proteinuria without change in creatinine
Answer: C. AKI is defined by a rapid decrease in kidney function over hours to days, characterized by an increase in serum creatinine or a decrease in urine output. KDIGO criteria: creatinine increase ≥0.3 mg/dL within 48h, or creatinine increase ≥1.5 times baseline within 7 days, or urine output <0.5 mL/kg/h for 6 hours.
In pre-renal acute kidney injury, urine sodium is typically ---
- > 40 mmol/L
- > 60 mmol/L
- < 20 mmol/L
- 20–40 mmol/L
Answer: C.