What causes AKI (acute kidney injury)?

What causes AKI (acute kidney injury)?

9 key causes of AKI

The ‘VOID-RIGHT’ mnemonic is useful:

1. V – vasculitis (e.g. lupus (SLE) nephritis; all rare)
2. O – obstruction 
3. I – infection (sepsis)
4. D – dehydration
5. R – renal artery stenosis (with bilateral thrombosis)
6. I – interstitial disease (acute tubular necrosis (ATN); drugs (e.g. antibiotics, NSAIS, ACE/ARBs, contrast nephropathy))
7. G – glomerulonephritis (e.g. crescentic IgA nephropathy; all rare)
8. H – haemolytic-uraemic syndrome (very rare; is it Friday!?)
9. T – thrombo-embolism (e.g. bilateral renal vein thrombosis; also very rare)

In this article we will describe these and other causes of AKI.

The causes of acute kidney injury can be divided into prerenal, renal and post-renal. These phrases mean problems with the blood supply to the kidneys (pre), the kidneys themselves (renal), and the urine drainage pipes or bladder (post).

Pre-renal

• Dehydration and infection (sepsis) are the commonest causes, partly as they cause hypotension (low blood pressure) which leads to a lack of blood going to the kidneys. Other causes include:
  • Bleeding (haemorrhage)
  • Cardiac failure
  • Low blood pressure (of other causes)
  • Liver failure
  • Bilateral renal artery thrombosis (e.g. usually occurs on the background of renal artery stenosis, RAS)
  • Bilateral renal vein thrombosis (can be a complication of severe nephrotic syndrome).

Renal

• Tubulo-interstitial disease (TID)
  • Acute Tubular Necrosis (ATN). This is the commonest TI cause. It is usually secondary to prolonged hypoperfusion (largely all the pre-renal causes). In ATN, the kidney is pre-programmed (for reasons we don’t understand) to ‘close down’ (blood goes to it and from it, but it is not filtered) for 10-14 days, and then it ‘opens up’ and starts doing its normal job again. Dialysis may be required during this period
  • Acute tubulointerstitial nephritis (TIN) – inflammation of tubes between the glomeruli (tiny filters; in the medulla (inner area) of the kidney). It can be caused by drugs, infections or autoimmune disease
  • Drugs toxic to the kidneys – e.g. NSAIDs, ACEi/ARBs, antibiotics (such as aminoglycosides like gentamicin), or chemotherapy (such as cisplatin) and the dye that is injected for CTs and other x-rays (contrast nephropathy)
• Autoimmune diseases (all rare), such as:
  • Glomerulonephritis (GN) (inflammation of tiny filters in the cortex (outer area) of the kidney)
  • Vasculitis (inflammation of small to medium sized blood vessels)
• Other: intra-tubular obstruction (multiple myeloma and rhabdomyolysis); or hepatorenal syndrome and haemolytic-uraemic syndrome (HUS; both very rare).

Post-renal

• In men, it is usually due to enlargement of the prostate gland (benign (BPH) or malignant)
• In women, pelvic cancer is commonest cause
• Bladder cancer is another cause and can affect men and women.

Note. Renal stones are not a common cause of AKI, but can do – usually if you have one kidney.

Multifactorial AKI

AKI is often multifactorial – e.g.

• Pre-, peri- and/or post-operative hypotension, combined with
• Sepsis, and
• Antibiotics to treat the sepsis.

Note. Hypotension often relates to the underlying cause, e.g. GI sepsis.

Summary

We have described the causes of AKI. We hope it has been useful.