Acute kidney injury
Investigations
1st investigations to order
basic metabolic profile (including blood urea nitrogen [BUN] and creatinine)
Test
Often an acutely elevated serum creatinine may be the initial or only sign of decline in renal function.
Result
acutely elevated serum creatinine, high serum potassium, metabolic acidosis
ratio of serum BUN to creatinine
Test
Consider other causes of elevated BUN (such as drug-induced elevations or gastrointestinal bleeding) when interpreting results.
Result
serum BUN to creatinine ratio ≥20:1 supports prerenal azotemia
urinalysis
Test
Collected as clean-catch specimen.
Patients with glomerular disease typically present with proteinuria and microscopic hematuria with hypertension and edema.
Result
red blood cells, WBCs, cellular casts, proteinuria, bacteria, positive nitrite and leukocyte esterase (in cases of infection)
urine culture
Test
Collected if there is suspicion of infection on initial urinalysis.
Result
bacterial or fungal growth may occur
complete blood count
Test
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.
结果
anemia, leukocytosis, thrombocytopenia
fractional excretion of sodium
检查
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
Exame
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
Exame
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
ტესტი
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.
შედეგი
diagnostic for metabolic acidosis and certain intoxications
fluid challenge
ტესტი
May be administered with crystalloid or colloid (but not hydroxyethyl starch solutions), and is both diagnostic and therapeutic in suspected prerenal azotemia.
შედეგი
renal function may improve rapidly in prerenal azotemia
bladder catheterization
ტესტი
Diagnostic and therapeutic for bladder neck obstruction in addition to providing an assessment of residual urine and a sample for analysis.
შედეგი
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
ტესტი
Evaluates maintenance of normal tubular function and response to antidiuretic hormone in cases of hypovolemia.
შედეგი
high in prerenal azotemia (the effect of dyes and mannitol must be excluded); close to serum osmolality in acute tubular necrosis
urine sodium concentration
ტესტი
High levels in acute tubular necrosis not exclusive to the diagnosis.
შედეგი
<20 mEq/L (suggests avid sodium retention in renal hypoperfusion and prerenal azotemia); high level (often with acute tubular necrosis)
renal ultrasound
ტესტი
Assists in evaluation of postobstructive causes as well as in the evaluation of renal architecture and size (underlying chronic kidney disease).
შედეგი
dilated renal calyces (suggesting obstruction), reduced corticomedullary differentiation, or small and sclerotic-appearing kidneys (suggesting chronic kidney disease)
chest x-ray
ტესტი
If renal failure is associated with heart failure.
შედეგი
may show signs of pulmonary edema and cardiomegaly
ECG
ტესტი
Changes may occur with severe hyperkalemia.
შედეგი
peaked T waves, increased PR interval, widened QRS, atrial arrest, and deterioration to a sine wave pattern (if severe hyperkalemia)
გასათვალისწინებელი კვლევები
antinuclear antibodies
ტესტი
Elevated titer is supportive of a diagnosis of systemic lupus erythematosus, which often has renal manifestations.
结果
normal or elevated
anti-DNA
检查
Elevated titer supports the diagnosis of systemic lupus erythematosus, which often has renal manifestations.
结果
normal or elevated
complement (C3, C4, CH50)
检查
Low complement levels support an active disease process, such as systemic lupus erythematosus.
结果
normal or depressed
anti-glomerular basement membrane antibodies
检查
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).
结果
normal or elevated
antineutrophil cytoplasmic antibodies
检查
Elevated titers are seen in vasculitic syndromes such as granulomatosis with polyangiitis (formerly known as Wegener granulomatosis), eosinophilic polyangiitis, and microscopic polyangiitis.
结果
normal or elevated titers
acute hepatitis profile
检查
The presence of positive serology in active hepatitis C is associated with renal conditions such as membranoproliferative glomerulonephritis and cryoglobulinemia.
结果
positive or negative serology
HIV serology
检查
HIV-associated nephropathy and certain drugs used in the management of HIV have renal complications.
结果
positive or negative
cryoglobulins
检查
The presence of cryoglobulins support cryoglobulin-associated renal disease, if AKI is present.
结果
positive or negative serology
erythrocyte sedimentation rate
检查
A normal erythrocyte sedimentation rate argues against the presence of inflammatory renal disease or embolic injury.
结果
normal or elevated
antistreptolysin-O antibody
检查
An elevated titer supports but does not make a diagnosis of an infectious glomerulonephritis.
结果
normal or elevated
abdominal computed tomography or magnetic resonance imaging scan
检查
Sometimes required to further evaluate cases of obstruction suggested on ultrasound.
结果
image of mass or stone may be present
nuclear renal flow scan
检查
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.
结果
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
检查
May be used if obstruction due to stenosis of the ureter is suspected.
结果
direct visualization and treatment of ureteral stenosis if present
renal biopsy
检查
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.
结果
changes associated with acute tubular necrosis, glomerulonephritis, vasculitis, or other intrinsic renal disease may be present
新兴检查
novel serum and urinary biomarkers
检查
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]
结果
results indicative of renal damage
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