Stethopedia | Approach

Approach to

Acute Kidney Injury

Confirm and stage AKI with KDIGO criteria, treat renal emergencies (hyperkalemia first; dialysis only if refractory), then sort the cause into pre-renal, intrinsic (tubulointerstitial, glomerular or vascular) or post-renal.

  1. Creatinine rising or urine output falling
  2. KDIGO: Cr ↑≥26.5 µmol/L (0.3 mg/dL) in 48 h, ≥1.5× in 7 d, or UOP <0.5 mL/kg/h ×6 h; stage 1–31
  3. K, VBG, ECG; volume; hold nephrotoxins; bladder scan; UA, sediment; urine Na, Cr, urea1,11
  4. Any renal emergency?

Renal emergency: treat now; call nephrology2,11

  • ECG change, K ≥6.0 mmol/L, or rising fast
  • Refractory pulmonary edema
  • pH <7.1 despite bicarbonate
  • Uremia: pericarditis, confusion
  • Lithium or toxic alcohol
  • RPGN: hemoptysis, RBC casts10,11

→ ECG change: Ca gluconate; K ≥6.5: shift K; dialyze if refractory2,8,11

If not: where is the injury?

CausesCluesWorkupManagement

Pre-renal

  • Volume loss: GI, bleeding, diuretics
  • Low EABV: heart failure, cirrhosis, sepsis
  • NSAIDs, ACEi/ARB
  • Orthostasis, dry mucosa; or congestion
  • Bland sediment, hyaline casts11
  • FENa <1% if off diuretics3,12
  • FEUrea ≤35% on diuretics: weak3,12
  • Dry: balanced crystalloid; hold diuretics7,11
  • HF congestion: diurese; Cr rise OK11
  • Cirrhosis: stop diuretics; albumin challenge11

Tubulointerstitial

  • ATN: ischemia, sepsis, contrast
  • AIN: β-lactams, PPIs, NSAIDs
  • Rhabdomyolysis; crystals (TLS)
  • Muddy brown casts, tubular cells: ATN4
  • New drug; fever, rash, sterile pyuria
  • Heme+ dipstick, no RBCs: rhabdo11
  • Fresh urine microscopy4
  • CK; urate, phosphate, LDH if TLS
  • Skip urine eosinophils (LR ~1)5
  • ATN: supportive; avoid nephrotoxins1
  • AIN: stop drug; steroids per nephrology
  • Rhabdo: early isotonic fluids; watch K9

Glomerular & vascular

  • RPGN: anti-GBM, ANCA vasculitis
  • Lupus, IgA, post-infectious GN
  • TTP/HUS, scleroderma crisis, atheroemboli
  • RBC casts, dysmorphic RBCs
  • Hemoptysis, rash, sinusitis
  • Schistocytes, low platelets, high LDH
  • ANCA, anti-GBM, C3/C4, ANA10
  • Smear, LDH, haptoglobin, ADAMTS13 if TMA
  • Biopsy if it will change treatment10
  • RPGN: steroids ± PLEX, nephrology today10,11
  • TTP: hematology, PLEX11
  • Scleroderma crisis: captopril11

Post-renal

  • Bladder outlet: BPH, anticholinergics
  • Blocked urinary catheter
  • Bilateral stones, pelvic mass
  • Anuria; palpable bladder
  • Prostatism, recurrent UTIs6
  • Bladder scan for retention
  • Renal US: hydronephrosis6
  • Foley; flush or replace blocked catheter
  • Fever + hydro: urgent decompression11
  • Watch for post-obstructive diuresis

Can't-miss cause Superscripts link to the references below.

References

  1. Kellum JA, Lameire N; KDIGO AKI Guideline Work Group. Diagnosis, evaluation, and management of acute kidney injury: a KDIGO summary (Part 1). Crit Care. 2013;17:204. PubMed 23394211
  2. James M, Bouchard J, Ho J, et al. Canadian Society of Nephrology commentary on the 2012 KDIGO clinical practice guideline for acute kidney injury. Am J Kidney Dis. 2013;61:673–685. PubMed 23518195
  3. Carvounis CP, Nisar S, Guro-Razuman S. Significance of the fractional excretion of urea in the differential diagnosis of acute renal failure. Kidney Int. 2002;62:2223–2229. PubMed 12427149
  4. Perazella MA, Coca SG, Kanbay M, et al. Diagnostic value of urine microscopy for differential diagnosis of acute kidney injury in hospitalized patients. Clin J Am Soc Nephrol. 2008;3:1615–1619. PubMed 18784207
  5. Muriithi AK, Nasr SH, Leung N. Utility of urine eosinophils in the diagnosis of acute interstitial nephritis. Clin J Am Soc Nephrol. 2013;8:1857–1862. PubMed 24052222
  6. Licurse A, Kim MC, Dziura J, et al. Renal ultrasonography in the evaluation of acute kidney injury: developing a risk stratification framework. Arch Intern Med. 2010;170:1900–1907. PubMed 21098348
  7. Semler MW, Self WH, Wanderer JP, et al. Balanced crystalloids versus saline in critically ill adults. N Engl J Med. 2018;378:829–839. PubMed 29485925
  8. STARRT-AKI Investigators. Timing of initiation of renal-replacement therapy in acute kidney injury. N Engl J Med. 2020;383:240–251. PubMed 32668114
  9. Bosch X, Poch E, Grau JM. Rhabdomyolysis and acute kidney injury. N Engl J Med. 2009;361:62–72. PubMed 19571284
  10. Rovin BH, Adler SG, Barratt J, et al. Executive summary of the KDIGO 2021 guideline for the management of glomerular diseases. Kidney Int. 2021;100:753–779. PubMed 34556300
  11. Gay E, Levy N, eds. Hepatorenal Syndrome; Acute Kidney Injury; Advanced Diuresis; Urinalysis & Nephrolithiasis; Transfusion Medicine. In: Department of Medicine Housestaff Manual, 30th ed. 2024:94, 96–97, 101, 108, 142.
  12. Pépin MN, Bouchard J, Legault L, Ethier J. Diagnostic performance of fractional excretion of urea and fractional excretion of sodium in the evaluations of patients with acute kidney injury with or without diuretic treatment. Am J Kidney Dis. 2007;50:566–573. PubMed 17900456

For education only; not a substitute for clinical judgment or local protocols. Where sources differ, the flowchart follows the current guideline.

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