Tests

1st tests to order

basic metabolic profile (including blood urea nitrogen [BUN] and creatinine)

Test
Result
Test

Often an acutely elevated serum creatinine may be the initial or only sign of decline in renal function.

Resultado

acutely elevated serum creatinine, high serum potassium, metabolic acidosis

ratio of serum BUN to creatinine

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Consider other causes of elevated BUN (such as drug-induced elevations or gastrointestinal bleeding) when interpreting results.

Resultado

serum BUN to creatinine ratio ≥20:1 supports prerenal azotemia

urinalysis

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Collected as clean-catch specimen.

Patients with glomerular disease typically present with proteinuria and microscopic hematuria with hypertension and edema.

Resultado

red blood cells, WBCs, cellular casts, proteinuria, bacteria, positive nitrite and leukocyte esterase (in cases of infection)

urine culture

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Collected if there is suspicion of infection on initial urinalysis.

Resultado

bacterial or fungal growth may occur

complete blood count

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Anemia is suggestive of possible chronic kidney disease, blood loss, or acute inflammation.

Leukocytosis may support infection.

Thrombocytopenia can be seen in rare disorders such as cryoglobulinemia, hemolytic uremic syndrome, or thrombotic microangiopathy.

Resultado

anemia, leukocytosis, thrombocytopenia

fractional excretion of sodium

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May also be seen in glomerulonephritis, hepatorenal syndrome, and some cases of obstruction, as long as tubular function remains intact.[99][100]​ Increased levels are also caused by diuretics.​​ The FENa is calculated as follows: (urine sodium x serum creatinine)/(serum sodium x urine creatinine) x 100%.

Resultado

<1% supports prerenal azotemia; typically <0.2% in hepatorenal syndrome

fractional excretion of urea

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Test used if patient has been exposed to diuretics. The fractional excretion of urea is calculated as follows: (urine urea x serum creatinine)/(serum urea x urine creatinine) x 100%. Fractional excretion of urea: calculator Opens in new window

Resultado

<35% supports prerenal azotemia

urinary eosinophil count

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Urinary eosinophil counts have low sensitivity and specificity for acute interstitial nephritis, but may be elevated in patients with pyuria.[98]

Some guidelines (e.g., the American Association for Clinical Chemistry) advise against routine use in the evaluation of AKI.[99]​ Eosinophiluria may also be seen with atheroembolic disease.

Resultado

>5% to 7% weakly supports a diagnosis of interstitial nephritis but is not diagnostic

venous blood gases

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Anion gap acidosis seen in acute and chronic renal failure due to impaired excretion of nonvolatile acids.

Assists in further evaluation of acidosis, which is often suggested by the low bicarbonate on the basic metabolic profile.

Resultado

diagnostic for metabolic acidosis and certain intoxications

fluid challenge

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May be administered with crystalloid or colloid (but not hydroxyethyl starch solutions), and is both diagnostic and therapeutic in suspected prerenal azotemia.

Resultado

renal function may improve rapidly in prerenal azotemia

bladder catheterization

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Diagnostic and therapeutic for bladder neck obstruction in addition to providing an assessment of residual urine and a sample for analysis.

Resultado

significant urine volume released after catheter placement (in cases of bladder outlet obstruction); minimal residual urine after catheter placement (in cases of impaired urine production or higher level obstruction)

urine osmolality

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Evaluates maintenance of normal tubular function and response to antidiuretic hormone in cases of hypovolemia.

Resultado

high in prerenal azotemia (the effect of dyes and mannitol must be excluded); close to serum osmolality in acute tubular necrosis

urine sodium concentration

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High levels in acute tubular necrosis not exclusive to the diagnosis.

Resultado

<20 mEq/L (suggests avid sodium retention in renal hypoperfusion and prerenal azotemia); high level (often with acute tubular necrosis)

renal ultrasound

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Assists in evaluation of postobstructive causes as well as in the evaluation of renal architecture and size (underlying chronic kidney disease).

Resultado

dilated renal calyces (suggesting obstruction), reduced corticomedullary differentiation, or small and sclerotic-appearing kidneys (suggesting chronic kidney disease)

chest x-ray

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If renal failure is associated with heart failure.

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may show signs of pulmonary edema and cardiomegaly

ECG

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Changes may occur with severe hyperkalemia.

Resultado

peaked T waves, increased PR interval, widened QRS, atrial arrest, and deterioration to a sine wave pattern (if severe hyperkalemia)

Investigações a serem consideradas

antinuclear antibodies

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Elevated titer is supportive of a diagnosis of systemic lupus erythematosus, which often has renal manifestations.

Resultado

normal or elevated

anti-DNA

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Elevated titer supports the diagnosis of systemic lupus erythematosus, which often has renal manifestations.

Resultado

normal or elevated

complement (C3, C4, CH50)

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Low complement levels support an active disease process, such as systemic lupus erythematosus.

Resultado

normal or depressed

anti-glomerular basement membrane antibodies

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Elevated antibody titers to the glomerular basement membrane, which may present in diseases of the kidney (e.g., Goodpasture syndrome and antiglomerular basement membrane syndrome).

Resultado

normal or elevated

antineutrophil cytoplasmic antibodies

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Elevated titers are seen in vasculitic syndromes such as granulomatosis with polyangiitis (formerly known as Wegener granulomatosis), eosinophilic polyangiitis, and microscopic polyangiitis.

Resultado

normal or elevated titers

acute hepatitis profile

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The presence of positive serology in active hepatitis C is associated with renal conditions such as membranoproliferative glomerulonephritis and cryoglobulinemia.

Resultado

positive or negative serology

HIV serology

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HIV-associated nephropathy and certain drugs used in the management of HIV have renal complications.

Resultado

positive or negative

cryoglobulins

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The presence of cryoglobulins support cryoglobulin-associated renal disease, if AKI is present.

Resultado

positive or negative serology

erythrocyte sedimentation rate

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A normal erythrocyte sedimentation rate argues against the presence of inflammatory renal disease or embolic injury.

Resultado

normal or elevated

antistreptolysin-O antibody

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An elevated titer supports but does not make a diagnosis of an infectious glomerulonephritis.

Resultado

normal or elevated

abdominal computed tomography or magnetic resonance imaging scan

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Sometimes required to further evaluate cases of obstruction suggested on ultrasound.

Resultado

image of mass or stone may be present

nuclear renal flow scan

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May be modified using captopril to evaluate for renal artery stenosis, or furosemide to evaluate for obstruction in cases of hydronephrosis where obvious mechanical obstruction is uncertain.

Resultado

normal scan reveals appropriate renal perfusion, tracer uptake, and excretion; impaired tracer excretion (supportive of acute tubular necrosis); poor blood flow (supportive of obstruction of blood supply); normal blood flow and tracer excretion with tracer accumulation in the collecting system (supportive of obstruction of the urine outflow tract)

cystoscopy

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May be used if obstruction due to stenosis of the ureter is suspected.

Resultado

direct visualization and treatment of ureteral stenosis if present

renal biopsy

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Biopsy is frequently required to further investigate positive serologic studies for suspected glomerulonephritis.

Biopsies are also done when the cause of kidney injury is unclear.

May confirm acute tubular necrosis, but not often performed for this diagnosis.

Resultado

changes associated with acute tubular necrosis, glomerulonephritis, vasculitis, or other intrinsic renal disease may be present

Novos exames

novel serum and urinary biomarkers

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Various novel serum and urinary biomarkers are showing potential as useful indicators for the diagnosis and classification of AKI and as predictors of mortality after AKI; however, further studies are needed to determine their clinical utility.​​[101][102][103][104][106][107]

Resultado

results indicative of renal damage

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