Difference Between Acute and Chronic Renal Failure

Acute vs Chronic Renal Failure | Acute Renal Failure vs Chronic Renal Failure | ARF vs CRF  

Acute renal failure is abrupt deterioration in renal function, which is usually, but not invariably reversible over a period of days or weeks, and usually accompanied by a reduction in urine volume. In contrast; chronic renal failure is the clinical syndrome of the metabolic and systemic consequences of a gradual, substantial and irreversible reduction in the excretory and homeostatic functions of the kidneys.

Both of these conditions, if untreated, ultimately results in end stage renal failure where the death is likely without renal replacement therapy, and this article points out the differences between acute and chronic renal failure with respect to their definition, temporal relationship, causes, clinical features, investigation findings, management and prognosis.

Acute Renal Failure (ARF)

It defines as a reduction in glomerular filtration rate (GFR) occurring over days or weeks. The diagnosis of ARF is made, if there is an increase in serum creatinine of >50 micro mol/L, or increase in serum creatinine of >50% from the baseline, or reduction in calculated creatinine clearance of >50%, or need for dialysis.

Causes of ARF are broadly categorized as pre-renal, intrinsic renal, post renal causes. Pre renal causes are severe hypovolemia, impaired cardiac pump efficiency, and vascular disease limiting renal blood flow. Acute tubular necrosis, renal parenchymal disease, hepato-renal syndrome are some of the causes of intrinsic renal failure and bladder outflow obstruction by pelvic malignancies, radiation fibrosis, bilateral stone disease are some of the causes of post renal failure.

In ARF, usually the patient presents with few warning signs at the early stages but may notice a reduction in urinary volume and features of intra vascular volume depletion in the later stages.

The cause may be obvious like gastrointestinal bleeding, burns, skin disease, and sepsis but can be hidden such as concealed blood losses, which can occur in trauma to the abdomen. Features of metabolic acidosis and hyperkalaemia are often present.

Once the clinical diagnosis is made, patient is investigated with urinary full report, electrolytes, serum creatinine, imaging. Ultra sound scan shows swollen kidneys and reduced cortico-medullary demarcation. Renal biopsy should be performed in all patients, with normal-sized, unobstructed kidneys, in whom the diagnosis of acute tubular necrosis causing acute renal failure is not suspected.

Principles of management of ARF include recognition and treatment of life-threatening complications such as hyperkalaemia and pulmonary oedema, recognition and treatment of intra vascular volume depletion and diagnosis of the cause and treat where possible.

Prognosis of acute renal ARF is usually determined by the severity of the underlying disorder and other complications. 

Chronic Renal Failure (CRF)

Chronic renal failure is defined as either kidney damage or a decreased glomerular filtration rate of <60ml/min/1.73m2 for 3 or more months comparing to ARF, which occurs suddenly or over a short period of time.

The most common cause could be chronic glomerulonephritis with ever increasing number of diabetic nephropathy leading to CRF becoming common. Other causes include chronic pyelonephritis, polycystic kidney disease, connective tissue disorders, and amyloidosis.

Clinically the patients presents with malaise, anorexia, itching, vomiting, convulsions etc. They may have a short stature, pale, show hyperpigmentation, bruising, signs of fluid over load and proximal myopathy.

Patient is investigated to make the diagnosis, stage the disease, and assess the complications.

Ultra sound scan of the kidney shows small kidneys, reduced cortical thickness, together with increased echogenecity; though renal size may remain normal in chronic renal failure, diabetic nephropathy, myeloma, adult poly cystic kidney disease, and in amyloidosis.

Principles of management include recognition and treatment of life threatening complications such as metabolic acidosis, hyperkalaemia, pulmonary edema, severe anaemia, identifying the cause and treat where possible and take general measures to reduce the progression of the disease.

The prognosis of patients with chronic renal failure shows that all cause mortality increases as kidney function decreases, but renal replacement therapy has shown increased survival, though the quality of life is severely affected.