The kidneys are vital organs of the body that help in removal of excess fluids as well as wastes from the blood and maintain electrolyte balance in the body. Declining functions of the kidneys lead to renal failure.

Renal failure is of basic two types:-

• Acute renal failure or acute kidney injury
• Chronic renal failure or chronic kidney injury

While acute renal failure is caused due to sudden failure of renal functions, chronic renal failure is the result of slow and progressive decline of renal functions.

The trends of creatinine rise in blood may help determine the progress of renal damage. While in acute kidney injury there is a sharper rise in creatinine in blood indicating sudden onset renal damage, in chronic renal damage the levels rise more gradually but progressively as the glomerular filtration rate (GFR) declines.

Acute renal injury or acute renal failure

Acute renal failure is the previous term given to acute renal injury. In this condition the kidney functions decline rapidly. The patient may present with declining volume of urine, electrolyte imbalances and accumulation of fluids in the body.

Depending on the cause of acute renal damage, acute renal injury is further classified as:-

• Prerenal failure including causes that reduce the blood flow to the kidneys. These include dehydration, severe fall in blood volume due to shock, blood loss or extensive burns, heart failure, cardiogenic shock,  anaphylactic shock, septic shock,
• Renal failure including those that are caused by diseases of the kidneys. This includes acute tubular necrosis, toxins and drugs that damage kidneys, hemoglobinuria, myoglobinuria, myeloma light chains, pyelonephritis or acute glomerulonephritis.
• Post renal failure is caused by obstruction of urine flow from the kidneys. This obstruction maybe at the level of the ureter or at the level of the outflow of the urinary bladder.

Chronic renal disease or chronic renal failure

Chronic kidney disease develops due to long term disease or damage to the kidneys. Commonly chronic renal failure is the end result of kidney damage caused by diseases such as diabetes, high blood pressure etc.

Acute-on-chronic renal failure

Acute renal failure or acute renal injury may develop in patients with chronic renal disease. This is called acute-on-chronic renal failure.

This condition is often difficult to distinguish from chronic renal failure and may be life threatening. In fact most people who present with acute renal injury already have some degree of chronic renal damage.

End-stage renal disease or ESRD

This is a condition where the kidney functions are almost totally absent with GFR less than 5% of normal. The renal tissues appear dried up along with fibrosis. Dialysis or transplantation of a healthy donor kidney is required for living at this stage.