Laboratory Tests for Suspected Renal Failure

Core Blood Tests

Serum creatinine is the primary marker for kidney function assessment and should be measured using an assay with calibration traceable to international standard reference materials 1
Estimated glomerular filtration rate (eGFR) should be calculated using the 2009 CKD-EPI equation rather than relying on serum creatinine concentration alone 1
Complete electrolyte panel including sodium, potassium, calcium, chloride, phosphorus, and magnesium to evaluate electrolyte imbalances 1
Cystatin C as a confirmatory test when eGFR based on serum creatinine may be less accurate 1
The combined creatinine-cystatin C equation provides improved accuracy in certain populations 1

Urine albumin-to-creatinine ratio (ACR) from an untimed urine sample is the preferred method for assessing proteinuria 1
Urinalysis with microscopy to detect cells, casts, and crystals, which can help differentiate between various causes of renal failure 1
Urine sodium concentration and fractional excretion of sodium (FENa) to differentiate between prerenal and intrarenal causes (FENa <1% suggests prerenal cause, while >1% indicates intrarenal damage) 2

Renal ultrasound should be performed to evaluate kidney size, echogenicity, and to rule out obstruction 3, 4
Unenhanced CT of the abdomen and pelvis may be useful for characterization of ultrasound-detected hydronephrosis and to determine the level and cause of obstruction 4, 5

A single abnormal test result is insufficient for diagnosis of chronic kidney disease; persistence of abnormalities for >3 months is required 1
Certain medications and substances can interfere with creatinine measurements, affecting eGFR accuracy 1
In patients with acute kidney injury superimposed on chronic kidney disease, interpreting blood test results requires comparison to baseline values 1
Iodinated contrast should be avoided in acute kidney injury unless there is an overriding clinical question that cannot be answered with an alternative imaging modality 3
Normal-sized kidneys on imaging do not exclude chronic kidney disease, as renal size is initially preserved in diabetic nephropathy or infiltrative disorders 4

Monitoring frequency should be guided by GFR category, albuminuria category, and rate of progression 1
More frequent monitoring is warranted for patients with rapidly declining kidney function or those at higher risk for progression 1
Annual screening with serum creatinine and urine albumin testing is recommended for patients with diabetes or hypertension 1