Acute kidney injury: workup and management

Acute kidney injury: creatinine rise of 0.3 mg/dL within 48 h, or 1.5 times baseline within 7 days, or urine output under 0.5 mL/kg/h for 6 h (KDIGO). Classify as pre-renal, intrinsic or post-renal and look for dialysis indications.

Working diagnosis Adult · US guidelines Draft · awaiting physician review

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01Orient

What's new in the evidence

BICARICU-2 (2025): sodium bicarbonate for severe metabolic acidemia with AKI did not improve 90-day mortality; reserve it for severe acidemia
Balanced crystalloids preferred over 0.9% saline for resuscitation (except traumatic brain injury); avoid synthetic colloids
STARRT-AKI (2020) and AKIKI-2 (2021): accelerated dialysis without urgent indications does not help
KDIGO has moved to living, modular updates; the 2012 AKI definition and staging still apply

Differential diagnoses

Pre-renal: hypovolemia, sepsis, heart failure, cirrhosis (hepatorenal)
Acute tubular necrosis (ischemic, contrast, aminoglycosides)
Acute interstitial nephritis (PPIs, beta-lactams, NSAIDs)
Glomerulonephritis
Obstruction (prostate, stones, malignancy, blocked catheter)
Rhabdomyolysis
Renal vascular causes (renal artery or vein thrombosis)

02Assess

Risk scores and decision tools

KDIGO AKI stage (creatinine and urine output)
FENa (or FEUrea on diuretics)
Furosemide stress test (urine <200 mL in 2 hours predicts progression)
Renal failure index; urine microscopy score for ATN

Key history questions

Baseline creatinine and prior CKD
Fluid losses, oral intake, diuretic use
Nephrotoxins: NSAIDs, ACEi/ARB, contrast, aminoglycosides, vancomycin
New drugs in the past 2-4 weeks (AIN)
Urinary symptoms, retention, hematuria
Rash, joint pain, hemoptysis (vasculitis)

Examination findings

Volume status: JVP, skin turgor, orthostatics, edema
Palpable bladder
Rash, livedo reticularis
Pericardial rub or asterixis (uremia)

03Investigate

Initial investigations

BMP with potassium and bicarbonate; repeat creatinine
Urinalysis with microscopy (casts, blood, protein, eosinophils)
Urine sodium and creatinine; FENa (FEUrea if on diuretics)
Bladder scan / post-void residual
Renal ultrasound
CK if rhabdomyolysis possible

Advanced investigations

Urine protein-to-creatinine ratio
ANA, ANCA, anti-GBM, complement, SPEP/free light chains if intrinsic disease suspected
Renal biopsy for unexplained intrinsic AKI

04Treat

Immediate management

Treat life-threatening hyperkalemia and acidosis
Urgent dialysis for refractory hyperkalemia, acidosis, fluid overload, uremic pericarditis or encephalopathy, or dialysable toxins
Relieve obstruction: bladder catheter; nephrostomy if upper-tract

First-line treatment

Restore volume with isotonic crystalloid if hypovolemic
Hold nephrotoxins and renally adjust all drugs
Pause ACEi/ARB, SGLT2i, diuretics and metformin until improving
Avoid IV contrast where possible

Second-line treatment

Stop the culprit drug in AIN; consider steroids with nephrology
Albumin with vasoconstrictor (terlipressin or norepinephrine) for hepatorenal AKI

Specialist referrals

Nephrology for stage 3, unclear cause, active sediment or dialysis need
Urology for obstruction

05Disposition

Admission criteria

KDIGO stage 2-3
Hyperkalemia, acidosis or fluid overload
Unable to maintain oral intake
Obstruction needing intervention

Safe discharge criteria

Stage 1 with clear reversible cause already addressed
Creatinine improving and electrolytes safe
Repeat labs arranged within 48-72 h

Follow-up timing

Repeat creatinine and electrolytes in 2-3 days, then at 3 months

Patient instructions

Avoid NSAIDs
Sick-day rules: pause metformin, ACEi/ARB, diuretics and SGLT2i during dehydrating illness

Monitoring

Daily BMP and weight
Strict input and output

Clinical pearls and pitfalls

FENa under 1% suggests pre-renal but is unreliable on diuretics
Muddy brown granular casts point to ATN; RBC casts point to glomerulonephritis

RefGuidelines and landmark evidence

GuidelineKDIGO – Clinical Practice Guideline for Acute Kidney Injury (2012)Free full text
TrialSTARRT-AKI: timing of renal-replacement therapy (2020)PublisherPubMed
TrialSMART: balanced crystalloids vs saline (Semler et al., 2018)Free full textPubMed
TrialBICARICU-2: bicarbonate for severe metabolic acidemia and AKI (2025)Free full textPubMed
TrialAKIKI 2: delayed strategies for starting renal replacement therapy (2021)PublisherPubMed

For education only. Typical adult starting points; confirm doses against renal function, allergies, interactions and your institution's protocols. Not a substitute for clinical judgment or senior review.