Investigations
1st investigations to order
basic metabolic profile (including urea and creatinine)
Test
Order as soon as possible and as routine follow-up in at-risk patients.
Creatinine is not a reliable indicator of renal failure as sudden decrease in glomerular filtration rate can over-estimate creatinine.
Changes in creatinine and urea levels can be influenced by other non-renal events such as rhabdomyolysis, nutritional state, use of steroids, or bleeding.[5]
Result
elevated serum creatinine, elevated urea, hyperkalaemia, or metabolic acidosis suggests ATN
urea-to-creatinine ratio
urine sodium concentration
Test
Tubule dysfunction leads to increased urinary sodium concentration.[5]
Result
elevated (>40 mmol/L [40 mEq/L])
urine osmolality
Test
Impairment in urinary concentrating capacity is characterised by decrease in urine osmolality.[5]
Can help differentiate between pre-renal azotaemia (in which the re-absorptive capacity and concentrating ability of the kidney are preserved or enhanced) and ATN (in which these functions are impaired).
Result
<450 mOsmol/kg supports ATN
fractional excretion of sodium
Test
Tubule dysfunction leads to increased fractional excretion of sodium.[5]
Low sensitivity and specificity for ATN. Also present in haemolysis, sepsis, cirrhosis, and chronic heart failure.
Result
over 2% supports ATN
fractional excretion of urea
Test
More reliable in patients taking diuretics or with chronic kidney disease.
Result
over 35% supports ATN[29]
urinalysis for sediment
Test
Can help distinguish from pre-renal azotaemia.[39]
Haem-positive urine in the absence of erythrocytes in the sediment suggests ATN from haemolysis or rhabdomyolysis.
Result
tubular epithelial cells, epithelial cell casts, or muddy brown casts supports ATN
FBC
Test
Mild to moderate anaemia is commonly observed in some types of ATN, such as in multiple myeloma, bleeding, haemolysis, or chronic kidney disease.
Result
anaemia
coagulation studies
Test
Prolonged ATN can result in bleeding as a result of dysfunctional platelets.
Result
prolonged PTT
urinary myoglobin
Test
Elevated myoglobin levels suggest ATN from rhabdomyolysis.
Result
elevated
Investigations to consider
arterial blood gases (ABG)
Test
Assists in further evaluation of acidosis, which is often suggested by the low bicarbonate on the basic metabolic profile.
Result
metabolic acidosis
platelet aggregation studies
Test
Prolonged ATN can result in bleeding as a result of platelet dysfunction.
Result
prolonged
ultrasound
Test
Assists in evaluation of post-obstructive causes as well as in the evaluation of renal architecture and size (underlying chronic kidney disease).
Result
normal in ATN
ECG
Test
May occur with hyperkalaemia.
Performed if hyperkalaemia is suspected or detected by laboratory tests.
Result
arrhythmias, peaked T waves, increased PR interval, widened QRS, atrial arrest, and deterioration to a sine wave pattern (if severe hyperkalaemia)
inferior vena cava (IVC) diameter measured by ultrasound
Test
Perform to assess intravascular volume status.
Result
IVC diameter >2.5 cm suggests volume overload; IVC diameter <1.5 cm suggests volume depletion[30]
renal biopsy
Test
Should only be performed when the history, clinical features, and findings of laboratory and radiological investigation suggest primary renal disease other than ischaemic or toxic-related ATN.[5]
Result
patchy and focal loss of individual cells or clusters of cells from tubular epithelium with resultant gaps, and exposure of areas of denudated basement membrane
serum and urinary biomarkers
Test
Various novel serum and urinary biomarkers are showing potential as useful indicators for the diagnosis and classification of acute kidney injury.[31][32] Kidney injury molecule-1 (KIM-1) has been shown to be a good early biomarker of ischaemic ATN.[33][34] Other biomarkers include neutrophil gelatinase-associated lipocalin (NGAL), interleukin-18 (IL-18), tissue inhibitor of metalloproteinase-2 (TIMP-2), and insulin-like growth factor binding protein 7 (IGFBP7).[35][36][37]
Result
results indicative of renal damage; confined to research studies, not widely applied to clinical settings[38]
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