Acute Renal Failure

Differentiating acute and chronic renal failure

The only two consistently useful indicators are:

1) Previous measurement of renal function

2) USS - long standing renal disease leads to loss of renal parenchyma and reduce renal size. A small less than ( 9 - 10 cm ) echobright and often cystic kidneys are characteristic of chronic kidney disease.

Exception is Diabetic nephropathy which tend to have relatively normal size kidney!

3) Laboratory are rarely helpful:

• Normal Hb argue against CKD but anaemia can be found in both CKD and ARF.
• Low calcium and high phosphate are secondary to impaired synthesis of vitamin D as found in patient with CKD.

Classification of ARF

Acute renal failure can be divided into pre-renal, renal and post-renal.

Intrinsic renal ARF - encompass all causes of ARF in which renal parenchyma has been damaged.

Large Blood Vessels

• Renal artery stenosis
• Cholesterol emboli
• Renal Vein thrombosis

Small Blood Vessels and Glomeruli

• Glomerulonephritis
• Vasculitis
• Scleroderma renal crisis
• Thrombotic microangiopathies
• Malignant hypertension
  

Tubulointerstitium

• Acute Interstitial Nephritis
• Cast nephropathy ( complicating myeloma )
• Contrast nephrotoxicity
  
• Tumour lysis
• Urate nephropathy
  

Acute Tubular Necrosis

• Ischaemic
• Nephrotoxic - aminoglycosides, myoglobin

The Nephritic and myeloma screen are necessary if an intrinsic renal cause of ARF ( but not ATN ) is suspected.

• Infection - 2 sets of blood cultures & ASO titre, HIV and Hepatitis serology with cryoglobulin level.
  
• Myeloma screen - plasma protein electrophoresis and immunoglobulin levels
  
• Anti-nuclear antibody ( ANA )
• Rheumatoid factor ( RF )
• Anti-neutrophil cytoplasmic antibody ( ANCA )
• Anti-glomerular basement membrane antibody ( anti-GBM )