Acute renal failure: tests
Pretest
True or False
Question 1
Several laboratory tests are useful for assessing the etiology of acute renal failure, and the findings can aid in proper management. These tests include
1. complete blood cell count,
2. serum biochemistries,
3. urine analysis with microscopy, and
4. urine electrolytes.
Question 2
True or False
Blood urea nitrogen and serum creatinine
1. Although increased levels of BUN and creatinine are the hallmarks of renal failure, the rate of rise is dependent on the degree of renal insult as well as protein intake with respect to BUN.
2. The ratio of BUN to creatinine is an important finding because the ratio can exceed 20:1 in conditions in which enhanced reabsorption of urea is favored (eg, in volume contraction) and suggests prerenal acute renal failure.
3. BUN may be elevated in patients with GI or mucosal bleeding, steroid treatment, or protein loading.
4. As a general rule, if serum creatinine increases to more than 1.5 mg/dL/d, rhabdomyolysis must be ruled out.
Question 3
True or False
CBC, peripheral smear, and serology
1. These tests may be useful, and the peripheral smear results may show schistocytes in conditions such as HUS or TTP.
2. A finding of increased rouleaux formation suggests multiple myeloma, and the workup should be directed toward immunoelectrophoresis of serum and urine.
3. The presence of myoglobin or free hemoglobin, increased serum uric acid level, and other related findings may help further define the etiology of acute renal failure.
4. Serologic tests for antinuclear antibody (ANA), ANCA, anti-GBM antibody, hepatitis, and antistreptolysin (ASO) and complement levels may help include and exclude glomerular disease.
Question 4
True or False
Urinalysis
1. Findings of granular muddy-brown casts are suggestive of tubular necrosis.
2. The presence of tubular cells or tubular cell casts also supports the diagnosis of ATN.
3. Often, oxalate crystals are observed in cases of ATN.
4. Reddish brown or cola-colored urine suggests the presence of myoglobin or hemoglobin, especially in the setting of a positive dipstick for heme and no RBCs in the microscopic examination.
Question 5
True or False
Dipstick assay findings may show the presence of
1. significant proteinuria, which would suggest glomerular or interstitial disease.
2. The presence of RBCs in the urine is always pathologic.
3. Eumorphic RBCs suggest bleeding along the collecting system.
4. Dysmorphic RBCs or RBC casts indicate glomerular inflammation, suggesting glomerulonephritis is present.
Question 6
True or False
The presence of WBCs or WBC casts
1. suggests pyelonephritis or acute interstitial nephritis.
2. The presence of urine eosinophils is helpful in establishing a diagnosis but is not necessary for allergic interstitial nephritis to be present.
3. The presence of eosinophils, as visualized with Wright stain or Hansel stain, suggests interstitial nephritis but can be seen in urinary tract infections, glomerulonephritis, and atheroembolic disease.
4. The presence of uric acid crystals may represent ATN associated with uric acid nephropathy and calcium oxalate crystals are usually present in cases of ethylene glycol poisoning.
Question 7
True or False
Urine electrolytes
1. Urine electrolyte findings also can serve as valuable indicators of functioning renal tubules.
2. The fractional excretion of sodium (FENa) is the commonly used indicator. However, the interpretation of results from patients in nonoliguric states, those with glomerulonephritis, and those receiving or ingesting diuretics can lead to an erroneous diagnosis.
3. FENa can be a valuable test for helping to detect extreme renal avidity for sodium in conditions such as hepatorenal syndrome. The formula for calculating the FENa is as follows:
· FENa = (UNa/PNa) / (UCr/PCr) X 100
Calculating the FENa is useful in acute renal failure only in the presence of oliguria.
4. In patients with prerenal azotemia, the FENa is usually less than 1%. In ATN, the FENa is greater than 1%. Exceptions to this rule are ATN caused by radiocontrast nephropathy, severe burns, acute glomerulonephritis, and rhabdomyolysis.
Question 8
True or False
In the presence of liver disease,
1. FENa can be less than 1% in the presence of ATN. On the other hand, because administration of diuretics may cause the FENa to be greater than 1%, these findings cannot be used as the sole indicators in acute renal failure.
2. In patients who are receiving diuretics, a fractional excretion of urea (FEUrea) can be obtained since urea transport is not affected by diuretics.
3. The formula for calculating the FEUrea is as follows:
· FEUrea = (Uurea/Purea) / (UCr/PCr) X 100
4. FEUrea of less than 35% is suggestive of a prerenal state.
Answers:
Question 1
Several laboratory tests are useful for assessing the etiology of acute renal failure, and the findings can aid in proper management. These tests include
1. complete blood cell count,
2. serum biochemistries,
3. urine analysis with microscopy, and
4. urine electrolytes.
Answer
TTTT
Question 2
True or False
Blood urea nitrogen and serum creatinine
1.Although increased levels of BUN and creatinine are the hallmarks of renal failure, the rate of rise is dependent on the degree of renal insult as well as protein intake with respect to BUN.
2. The ratio of BUN to creatinine is an important finding because the ratio can exceed 20:1 in conditions in which enhanced reabsorption of urea is favored (eg, in volume contraction) and suggests prerenal acute renal failure.
3.BUN may be elevated in patients with GI or mucosal bleeding, steroid treatment, or protein loading.
4.As a general rule, if serum creatinine increases to more than 1.5 mg/dL/d, rhabdomyolysis must be ruled out.
Answer
TTTT
Question 3
True or False
CBC, peripheral smear, and serology
1. These tests may be useful, and the peripheral smear results may show schistocytes in conditions such as HUS or TTP.
2. A finding of increased rouleaux formation suggests multiple myeloma, and the workup should be directed toward immunoelectrophoresis of serum and urine.
3. The presence of myoglobin or free hemoglobin, increased serum uric acid level, and other related findings may help further define the etiology of acute renal failure.
4. Serologic tests for antinuclear antibody (ANA), ANCA, anti-GBM antibody, hepatitis, and antistreptolysin (ASO) and complement levels may help include and exclude glomerular disease.
Answer
TTTT
Question 4
True or False
Urinalysis
1. Findings of granular muddy-brown casts are suggestive of tubular necrosis.
2.The presence of tubular cells or tubular cell casts also supports the diagnosis of ATN.
3.Often, oxalate crystals are observed in cases of ATN.
4.Reddish brown or cola-colored urine suggests the presence of myoglobin or hemoglobin, especially in the setting of a positive dipstick for heme and no RBCs in the microscopic examination.
Answer
TTTT
Question 5
True or False
Dipstick assay findings may show the presence of
1.significant proteinuria, which would suggest glomerular or interstitial disease.
2.The presence of RBCs in the urine is always pathologic.
3.Eumorphic RBCs suggest bleeding along the collecting system.
4.Dysmorphic RBCs or RBC casts indicate glomerular inflammation, suggesting glomerulonephritis is present.
Answer
TTTT
Question 6
True or False
The presence of WBCs or WBC casts
1.suggests pyelonephritis or acute interstitial nephritis.
2.The presence of urine eosinophils is helpful in establishing a diagnosis but is not necessary for allergic interstitial nephritis to be present.
3.The presence of eosinophils, as visualized with Wright stain or Hansel stain, suggests interstitial nephritis but can be seen in urinary tract infections, glomerulonephritis, and atheroembolic disease.
4.The presence of uric acid crystals may represent ATN associated with uric acid nephropathy and calcium oxalate crystals are usually present in cases of ethylene glycol poisoning.
Answer
TTTT
Question 7
True or False
Urine electrolytes
1. Urine electrolyte findings also can serve as valuable indicators of functioning renal tubules.
2.The fractional excretion of sodium (FENa) is the commonly used indicator. However, the interpretation of results from patients in nonoliguric states, those with glomerulonephritis, and those receiving or ingesting diuretics can lead to an erroneous diagnosis.
3.FENa can be a valuable test for helping to detect extreme renal avidity for sodium in conditions such as hepatorenal syndrome. The formula for calculating the FENa is as follows:
· FENa = (UNa/PNa) / (UCr/PCr) X 100
Calculating the FENa is useful in acute renal failure only in the presence of oliguria.
4.In patients with prerenal azotemia, the FENa is usually less than 1%. In ATN, the FENa is greater than 1%. Exceptions to this rule are ATN caused by radiocontrast nephropathy, severe burns, acute glomerulonephritis, and rhabdomyolysis.
Answer
TTTT
Question 8
True or False
In the presence of liver disease,
1.FENa can be less than 1% in the presence of ATN. On the other hand, because administration of diuretics may cause the FENa to be greater than 1%, these findings cannot be used as the sole indicators in acute renal failure.
2.In patients who are receiving diuretics, a fractional excretion of urea (FEUrea) can be obtained since urea transport is not affected by diuretics.
3.The formula for calculating the FEUrea is as follows:
· FEUrea = (Uurea/Purea) / (UCr/PCr) X 100
4.FEUrea of less than 35% is suggestive of a prerenal state.
Answer
TTTT
Modified from http://www.emedicine.com/med/topic1595.htm