Acute Kidney Injury Nephrology Physiotherapy

Definition and Causes of Acute Kidney Injury or Acute Renal Failure

In this article we will discuss the Definition and Causes of Acute Kidney Injury or Acute Renal Failure

In this article, we will discuss the Definition and Causes of Acute Kidney Injury or Acute Renal Failure. So, let’s get started.


Acute renal failure (ARF) or acute kidney injury (AKI) is defined as sudden and most often reversible loss of renal functions, which develops over a period of day or weeks, leads to retention of waste products of metabolism such as urea and creatinine. An increase in plasma creatinine concentration to >200 mol/L (>2 mg%) is often taken as the biochemical definition of renal failure. A reduction in urine output (oliguria)occurs usually but not always.

Oliguria is defined as urine output <100 ml/day while anuria is defined as either no urine passed or just not more than 50 ml passed in 24 hours.

Acute on chronic renal failure: Sudden deterioration of renal functions with rapid rise in blood urea and creatinine with fall in GFR (urine output) in a patient of established chronic renal failure is called acute on chronic renal failure.

Stages of AKI

Stage 1: It is a 1.0 to 1.5 fold increase in serum creatinine or a decline in urinary output to 0.5 ml/kg/hr over 6-12 hours.

Stage 2: It is 2.0 to 2.9 fold increase in serum creatinine or decline in urinary output to 0.5 ml/kg/hr over 12 hours or longer.

Stage 3: It is a 3-fold or greater increase in
serum creatinineor decline in urinary
output to less than 0.3 ml/kg/hr for 24 hours or longer or anuria for 12 hours or longer.


Depending on the cause, acute renal failure is classified into three groups:
1. Pre-renal: Cause lies outside the kidney, is commonly due to contraction of blood volume.
2. Renal: Cause lies inside the kidney (intrinsic renal disease).
3. Post-renal: Cause lies below the kidney in its excretory passage, i.e. pelvis, ureter, bladder and urethra.

The most common causes of ARF are blood loss, fluid and electrolyte depletion, diarrhoea, non-diarrhoeal G.I. infections, glomerulonephritis, poisoning (drugs, snake venom, heavy metals) and G6PD deficiency associated with intravascular hemolysis. Fluid depletion is the major cause of ARF in tropics due to infectious diarrhoea leading to hypovolaemia. Heat stroke is another cause in tropics. Infectious diarrhoea is also a common cause in children.

Acute glomerulonephritis and RPGN together account for large number of cases of ARF in children.

Malaria is a common cause of ARF in tropical countries. Falciparum infection causes most of these cases due to intravascular haemolysis or heavy parasitaemia. Intravascular haemolysis in malaria could also be drug-induced in patients with G6PD deficiency. Leptospirosis can also lead to ARF but is rare in India.

Acute interstitial nephritis due to
drugs (B-lactams, sulfonamides, NSAIDs, rifampicin), herbal indigenous medicine and certain bacterial and viral infections are emerging as important causes of ARF.

Septic abortions, pre-eclampsia, abruptio placentae, placenta previa and postpartum ARF are important obstetric causes of ARF.

Obstructive uropathy (stone, tumour
retroperitoneal fibrosis) is also an important but least common group leading to ARF.Benign hypertrophy of prostate is another important cause of reversible ARF.

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