Mr. T is 77-year-old man with acute renal failure (ARF).
|What is the differential diagnosis of ARF? How would you frame the differential?|
ARF is defined as an abrupt decrease in glomerular filtration rate (GFR), with a concomitant increase in serum creatinine, resulting in an inability to maintain fluid and electrolyte balance. It occurs over hours or days and can occur in the presence of previously normal renal function or in patients with chronic kidney disease (CKD). There is no standard definition, and criteria commonly used include an increase in serum creatinine of > 0.5 mg/dL, an increase of more than 20% above baseline, or a decrease in GFR of at least 50%.
The framework for the differential diagnosis is a combination of anatomic and pathophysiologic:
Prerenal (due to renal hypoperfusion)
GI fluid loss
Decreased effective circulating volume
Heart failure (HF)
Anesthesia- and medication-induced
Relative hypotension below patient's autoregulatory level
Changes in renal hemodynamics
Nonsteroidal antiinflammatory drugs (NSAIDs)/ cyclooxygenase (COX)-2 inhibitors
ACE inhibitors/angiotensin receptor blockers (ARBs)
Renal artery thrombosis or embolism
Abdominal aortic aneurysm
Thrombotic thrombocytopenic purpura
Hemolytic uremic syndrome
Disseminated intravascular coagulopathy
Postinfectious glomerulonephritis (GN)
Systemic lupus erythematosus
Antineutrophil cytoplasmic antibody associated GN
Anti-glomerular basement membrane disease
Tubular injury (acute tubular necrosis [ATN])
Ischemic, due to prolonged renal hypoperfusion
Medications (such as aminoglycosides)
Heavy metals (cisplatinum)
Intratubular pigments (myoglobin, hemoglobin), crystals (uric acid, oxalate), or proteins (myeloma)
Acute interstitial nephritis
Infiltration (lymphoma, sarcoidosis)
Ureteral (must be bilateral obstruction to cause ARF)
Retroperitoneal adenopathy or fibrosis
Benign prostatic hyperplasia (BPH) or prostate cancer
Obstructed indwelling catheters
An algorithm outlining the diagnostic approach to acute renal failure appears at the end of the chapter.
Measuring Kidney Function
Best overall measure of kidney function
Normal = 130 mL/min/1.73m2 in young men (120 mL/min/ 1.73m2 in women)
Difficult to accurately measure in clinical practice
Generation determined by muscle mass and dietary intake
Level varies with age, sex, race or ethnic group, muscle mass, diet, nutritional status
The relationship between creatinine and GFR varies inversely and exponentially, so that relatively small changes in serum creatinine may reflect significant decreases in GFR (Figure 25–1).
Creatinine is filtered by glomeruli and secreted by proximal tubule, so creatinine clearance exceeds GFR.
Must be calculated with a 24-hour urine collection, which is inconvenient for patients and often incomplete.
Freely filtered by glomerulus
Less variable than creatinine
Not yet in widespread use
Cockcroft-Gault formula (multiply by 0.85 for women):
Systematically overestimates GFR
Does not adjust for body surface ...