Chapter 13 of 155% of exam

Renal System

Renal content covers acid-base, fluid and electrolyte disorders, acute and chronic kidney disease, structural disease, neoplasms, renovascular disease and rhabdomyolysis. Many items require a small calculation or the reading of urine indices.

Acute kidney injury

Urine indices and the history separate prerenal, intrinsic and postrenal causes. Muscle breakdown can injure the kidney through pigment. Obstruction should be excluded with bladder volume or ultrasound.

Prerenal pattern

FENa below 1% and BUN-to-creatinine ratio above 20.

Merck Manual Professional Edition, Acute Kidney Injury

Rhabdomyolysis

Heme-positive dipstick without red cells and a high CK; aggressive IV fluids.

Merck Manual Professional Edition, Rhabdomyolysis

Postrenal

Check post-void residual or renal ultrasound for obstruction.

Merck Manual Professional Edition, Acute Kidney Injury

Acid-base and electrolytes

Compute the anion gap before naming the cause of a metabolic acidosis. Sodium disorders are approached by volume status. Chronic hyponatremia must be corrected slowly.

Anion gap

Sodium minus the sum of chloride and bicarbonate; high-gap causes include methanol and ethylene glycol, while diarrhea causes a normal-gap acidosis.

Merck Manual Professional Edition, Metabolic Acidosis

Osmotic demyelination

Too-rapid correction of chronic hyponatremia can cause it.

Merck Manual Professional Edition, Hyponatremia

Hyponatremia by volume

Hypovolemic: saline; hypervolemic: fluid restriction; euvolemic: treat the cause.

Merck Manual Professional Edition, Hyponatremia

Glomerular and structural disease

Nephrotic and nephritic syndromes are recognized by their urine and serum picture. Inherited cystic disease has extrarenal associations. Renovascular disease is a secondary cause of hypertension.

Nephrotic syndrome

Heavy proteinuria, hypoalbuminemia, edema and hyperlipidemia.

Merck Manual Professional Edition, Overview of Nephrotic Syndrome

ADPKD

Enlarged cystic kidneys, hypertension, hematuria and intracranial aneurysms.

Merck Manual Professional Edition, Autosomal Dominant Polycystic Kidney Disease

Renovascular hypertension

Diagnosed with duplex ultrasound, CT or MR angiography.

Merck Manual Professional Edition, Renovascular Hypertension

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