ITN/ATN/Prerenal uraemia

Question 1

Interstitial nephritis : definition

Answer 1

acute inflammation of the glomerular tubules and interstitium - the connective tissue between the cells and tubules in the kidneys

Question 2

Interstitial nephritis : Histology

Answer 2

Marked interstitial oedema and infiltrate in the connective tissue between renal tubules

Question 3

Interstitial nephritis : Causes

Answer 3

This is caused by a hypersensitivity reaction to;
* Drugs : Penicillin, NSAID, Rifampicin, Allopurinol, Furosemide
* Systemic disease : SLE, Sarcoidosis
* Infection

Question 4

Interstitial nephritis : Clinical features

Answer 4

• AKI - intra renal
• Hypertension
• Rash, fever, eosinophilia } sx of generalised hypersensitivity reaction

Question 5

Pre-renal uraemia : Definition

Answer 5

• Excess urea and waste products in the blood
• due to failure of the kidneys to filter waste products
• as a result of renal hypoperfusion

Question 6

Pre-renal uraemia : Pathophysiology

Answer 6

1. Decreased blood flow to the kidney - reduces its eGFR
2. Low eGFR - Activates RAAS - Aldosterone is released
   - Increases N+ reabsorbtion and water retention
   - Na+ reabsorption is tied to urea reabsorption } more urea in the blood

Less waste products + Increased reabsorption : Urea accumulate in the blood

Question 7

Pre-renal uraemia : Causes

Answer 7

Same as for pre-renal AKI
1. Fluid loss : Burns, dehydration, V+D
2. Congestive HF, Sepsis

Question 8

Pre-renal uraemia : Clinical features

Answer 8

• Uraemia : Confusion, lethargy, asterixis, nausea
• Oliguria : Urine output < 400ml
• Denydration/Hypovolaemia

Question 9

Acute tubular necrosis : definition

Answer 9

• Ischaemia or nephrotoxins cause injury and result in necrosis of renal tubular epithelial cells.
• Acute tubular necrosis (ATN) due to prolonged or severe ischaemia, the most common form of AKI, is preceded by impaired kidney perfusion and tissue hypoxaemia

Question 10

Acute tubular necrosis : Pathophysiology

Answer 10

1. Death of tubular epithelial cells
2. Distrupt basolateral surface
3. Detach from basement membrane and obstruct tubule } increase in tubular hydrostatic pressure
4. Decrease in egFR
5. Reduced filtration and urine output

Question 11

Acute tubular necrosis : Causes

Answer 11

1. Chronic hypoperfusion - shock, sepsis, dehydration
2. Nephrotoxins - Contrast dyes, Gentamicin, Nsaids

Question 12

Acute tubular necrosis : Investigations

Answer 12

Urinalysis : Muddy, brown casts indicate renal tubular epithelial cells in the urine and are specific to acute tubular necrosis.

Question 13

Acute tubular necrosis vs Pre-renal uraemia

Answer 13

1. Acute tubular necrosis } 2nd to kidney injury
   * Poor fluid response to fluid challenge
   * Dysfunction kidney : increased loss of N+ in the urine
   - High urine sodium } Low urine osmolality
   * Less urea in the blood
   * Urinalysis : Brown, granular casts
2. Pre renal uraemia
   * Good response to fluid challenge } likely 2nd to ischaemia
   * Increased Na+ retention } 2nd to RAAS thus
   - Low urinary sodium
   - High urine osmolality
   * Raised urea:creatitine ratio
   * Urinalysis : Normal sediment