Acute Kidney Injury (ATN)
Acute tubular necrosis is the most common cause of intrinsic AKI, resulting from ischemic or nephrotoxic injury to renal tubular epithelial cells. [1-2] It is a clinical-pathologic diagnosis often made presumptively based on history, urine studies, and exclusion of prerenal/postrenal causes. [2] The following is a comprehensive clinical summary organized for emergency medicine and primary care workflows.
History
- Key HPI questions: Onset and duration of decreased urine output; recent hypotensive episodes, surgeries, or ICU stays; exposure to nephrotoxic drugs or contrast agents; symptoms of volume depletion (vomiting, diarrhea, hemorrhage); dark or cola-colored urine (rhabdomyolysis/hemolysis) [1][3]
- Symptom characterization: Oliguria or anuria is the hallmark; may be nonoliguric in ~30–40% of cases (especially nephrotoxic ATN). Patients may report fatigue, nausea, edema, or dyspnea from volume overload [4-5]
- Timing: Ischemic ATN typically develops 24–72 hours after the insult; aminoglycoside-related ATN may appear 5–10 days into therapy; contrast-induced ATN peaks at 48–72 hours [5-6]
- Important negatives: Absence of obstructive symptoms (hesitancy, retention), absence of rash/fever/eosinophilia (argues against AIN), absence of hematuria/proteinuria (argues against glomerulonephritis) [3][5]
Alarm Features
- Anuria or oliguria (<0.3 mL/kg/h for ≥24 hours) [7-8]
- Refractory hyperkalemia with ECG changes (peaked T waves, widened QRS, sine wave) [9-10]
- Severe metabolic acidosis (pH <7.20, bicarb <12) unresponsive to medical therapy [9]
- Pulmonary edema/volume overload refractory to diuretics [7][9]
- Uremic symptoms: encephalopathy, pericarditis, bleeding diathesis [9]
- Unstable vital signs or signs of ongoing shock/sepsis [7]
Medications
- Common nephrotoxic causes of ATN:
- Medications to discontinue immediately: NSAIDs, ACE inhibitors/ARBs, diuretics, aminoglycosides, and any other nephrotoxins [6][13][16]
- Dose-adjust renally cleared drugs: antibiotics, anticoagulants, opioids, digoxin [6]
- Treatments for complications:
Diet
- Acute phase: Restrict potassium intake (<2 g/day), restrict sodium (<2 g/day), limit phosphorus [10]
- Fluid management: In oliguric patients, restrict daily intake to ~400 mL + previous day's urine output unless volume-depleted [10]
- Protein: Adequate but not excessive protein intake (0.8–1.0 g/kg/day in non-dialysis patients; higher if on CRRT) to avoid worsening azotemia [17]
- Long-term: Nutritional consultation recommended for critically ill patients; enteral nutrition preferred over parenteral [18]
Review of Systems
- Cardiovascular: Chest pain (uremic pericarditis), dyspnea, orthopnea, edema (volume overload)
- Neurologic: Confusion, asterixis, seizures (uremic encephalopathy)
- GI: Nausea, vomiting, anorexia (uremia), diarrhea or GI bleeding (precipitant or complication)
- Musculoskeletal: Muscle pain, weakness, dark urine (rhabdomyolysis as cause)
- Hematologic: Easy bruising, bleeding (uremic platelet dysfunction)
- Infectious: Fever, chills (sepsis as precipitant — sepsis causes 30–70% of ATN-related deaths) [18]
Collateral History and Family History
- Collateral: Medication reconciliation (OTC NSAIDs, herbal supplements), recent procedures/surgeries, contrast exposure, baseline creatinine from prior records, recent hospitalizations
- Family history: Generally not a major contributor to ATN; however, family history of CKD or polycystic kidney disease may affect baseline renal reserve
- Social context: Occupational heat exposure, substance use (cocaine → rhabdomyolysis), alcohol use (hepatorenal considerations), access to follow-up care
Risk Factors
- Pre-existing CKD (strongest risk factor for non-recovery) [19-20]
- Advanced age [21]
- Sepsis/septic shock (most common cause of ATN in ICU — 47% of severe AKI cases) [2][22]
- Major surgery (especially cardiac, vascular) [22]
- Hypovolemia/hemorrhage [2]
- Heart failure/cardiogenic shock [16]
- Cirrhosis [13]
- Diabetes mellitus [3]
- Multiple nephrotoxin exposure (polypharmacy) — 22% of inpatient AKI events meet nephrotoxic AKI criteria [15]
- Rhabdomyolysis (crush injury, statins, seizures, immobilization) [23-24]
Differential Diagnosis
- Prerenal azotemia (most common AKI cause overall) — responds to volume resuscitation within 24–48 hours; FENa <1%, urine osmolality >500 mOsm/kg [2][5]
- Acute interstitial nephritis (AIN) — fever, rash, eosinophilia; WBC casts on urine microscopy; drug-related (beta-lactams, PPIs, checkpoint inhibitors) [5]
- Postrenal obstruction — bilateral hydronephrosis on ultrasound; BPH, malignancy, nephrolithiasis [2-3]
- Glomerulonephritis — RBC casts, dysmorphic RBCs, heavy proteinuria; FENa <1% [5][25]
- Hepatorenal syndrome (HRS-AKI) — in cirrhosis; FENa <0.1%, bland sediment; responds to vasoconstrictors + albumin [13][26]
- Thrombotic microangiopathy (TMA/HUS/TTP) — schistocytes, thrombocytopenia, elevated LDH [5]
- Atheroembolic disease — post-procedure, livedo reticularis, eosinophilia, blue toes [5]
Past Medical History
- Prior AKI episodes (recurrent AKI within 12 months occurs in ~25% of patients) [20]
- Baseline CKD stage (affects recovery likelihood and management thresholds)
- Diabetes, hypertension, heart failure, liver disease
- Prior kidney transplant
- History of nephrolithiasis or urologic surgery (postrenal risk)
- Chronic NSAID or nephrotoxin use
Physical Exam
- Vital signs: Hypotension (ischemic cause), tachycardia (hypovolemia), hypertension with pulmonary edema (volume overload), fever (sepsis/infection) [7]
- Volume status assessment (critical first step):
- Skin: Livedo reticularis (atheroemboli), maculopapular rash (AIN), track marks (rhabdomyolysis from drug use)
- Abdomen: Palpable bladder (obstruction), ascites (cirrhosis), flank tenderness
- Cardiac: Pericardial friction rub (uremic pericarditis), murmurs
- Neurologic: Asterixis, altered mental status (uremic encephalopathy)
Lab Studies
The FENa calculator can help differentiate prerenal from intrinsic AKI:
Imaging
- First-line: Renal ultrasound — assess kidney size (normal or enlarged in ATN), echogenicity, and rule out hydronephrosis (postrenal obstruction) [3][16]
- Normal-sized kidneys with increased cortical echogenicity is typical of ATN
- Small kidneys suggest underlying CKD rather than acute process
- CT abdomen/pelvis without contrast if obstruction suspected but ultrasound equivocal
- Imaging is unnecessary when the clinical picture clearly points to ATN (e.g., post-septic shock with muddy brown casts and FENa >2%) and there are no risk factors for obstruction
Special Tests
- Urine microscopy scoring: Muddy brown granular casts and renal tubular epithelial cells — a urine sediment score ≥3 has high specificity for ATN [5][18]
- KDIGO staging for AKI severity (Stages 1–3 based on creatinine rise and urine output) [8][16]
- Novel biomarkers (limited clinical availability): NGAL (predicts severe AKI; may distinguish ATN from HRS in cirrhosis), TIMP-2 × IGFBP-7 (FDA-approved for AKI prediction), CCL14 (persistence of severe AKI) [20]
- Renal biopsy: Reserved for unclear etiology, suspected glomerulonephritis, AIN not responding to drug withdrawal, or prolonged AKI without recovery [2][5]
ECG
- Indications: Obtain in all patients with AKI and hyperkalemia or suspected uremic pericarditis
- Hyperkalemia progression:
- Uremic pericarditis: Diffuse ST elevation, PR depression (though often absent in uremic pericarditis)
- Any ECG changes from hyperkalemia = emergent treatment required (IV calcium gluconate first) [10]
Assessment
- ATN is a clinical diagnosis made by identifying a precipitating ischemic or nephrotoxic insult, excluding prerenal and postrenal causes, and finding characteristic urine findings (muddy brown casts, FENa >1%, urine osmolality <350) [5][18]
- Severity stratification per KDIGO: Stage 1 (Cr ↑ ≥0.3 mg/dL or 1.5×), Stage 2 (Cr ↑ 2–2.9×), Stage 3 (Cr ↑ ≥3× or ≥4 mg/dL or need for RRT) [8][16]
- Oliguric ATN carries worse prognosis than nonoliguric ATN and is more likely to require dialysis [16]
- Complications: Hyperkalemia, metabolic acidosis, volume overload, uremia, infection (sepsis causes 30–70% of ATN deaths), CKD progression [4][10][18]
- Prognosis: >85% of patients with ATN on previously normal kidneys recover sufficient renal function within 6–12 months; in-hospital mortality remains ~50% in severe cases requiring RRT, largely driven by the underlying illness [19][21][30]
Treatment Plan
Initial stabilization
- Assess and optimize volume status — isotonic crystalloid for hypovolemia; diuretics for overload [3][16]
- Discontinue all nephrotoxins (NSAIDs, aminoglycosides, contrast, ACEi/ARBs) [6][13][16]
- Treat the underlying cause (antibiotics for sepsis, fluids for rhabdomyolysis, relieve obstruction) [3][23]
Supportive management
- Maintain euvolemia; avoid both hypovolemia and fluid overload [16-17]
- Correct electrolyte abnormalities (hyperkalemia, hyperphosphatemia, acidosis) [10]
- Adjust all medication doses for renal function [6]
- Avoid unnecessary IV lines, catheters, and ventilators to reduce infection risk [18]
- Nutritional support: enteral preferred; adequate calories with appropriate protein [17-18]
Renal replacement therapy (RRT)
- Urgent indications: Refractory hyperkalemia, refractory metabolic acidosis, refractory pulmonary edema, uremic complications (pericarditis, encephalopathy, bleeding) [9]
- Nonurgent indications: BUN >112 mg/dL, oliguria/anuria >72 hours [9][20]
- Timing: In the absence of urgent indications, a watchful waiting approach is supported by the STARRT-AKI, AKIKI, and IDEAL-ICU trials — early initiation does not improve mortality and ~40–50% of deferred patients never require RRT [16][20][31]
- CRRT preferred in hemodynamically unstable patients; intermittent HD for stable patients [16][23]
The following table from the NEJM summarizes indications for kidney-replacement therapy:
Disposition
- Admission criteria:
- Nephrology consultation triggers: Stage 3 AKI, unclear etiology, need for RRT, preexisting CKD stage 4+, inadequate response to supportive care, suspected glomerulonephritis or vasculitis [3]
- Observation: Mild AKI (Stage 1) with clear reversible cause (e.g., NSAID use in otherwise healthy patient) may be managed with close outpatient follow-up if creatinine is trending down and electrolytes are stable
Follow Up / Return Precautions
- Post-discharge follow-up: Recheck creatinine and electrolytes within 1–2 weeks; nephrology follow-up within 1–3 months for Stage 2–3 AKI [20]
- Long-term monitoring: AKI survivors have increased risk of CKD, cardiovascular events, and recurrent AKI (25% recurrence within 12 months). Monitor creatinine, proteinuria, and blood pressure at 3 months and annually thereafter [20]
- Recovery timeline: If prerenal component is corrected early, creatinine may improve within 24–48 hours; established ATN typically requires several days to weeks for recovery; most recover within 6–12 months [6][19][30]
- Return precautions for patients:
- Decreased urine output or no urine output
- Swelling in legs/face, sudden weight gain, shortness of breath
- Confusion, excessive drowsiness
- Nausea/vomiting preventing oral intake
- Chest pain or palpitations
- Counseling: Avoid NSAIDs and nephrotoxins long-term; stay hydrated; inform all providers of AKI history; future contrast studies require pre-hydration protocols [6]
References
1. Acute Kidney Injury: Medical Causes and Pathogenesis. — Turgut F, Awad AS, Abdel-Rahman EM. Journal of Clinical Medicine. 2023.
2. Acute Kidney Injury: An Increasing Global Concern. — Lameire NH, Bagga A, Cruz D, et al. Lancet. 2013.
3. Acute Kidney Injury: Diagnosis and Management. — Mercado MG, Smith DK, Guard EL. American Family Physician. 2019.
4. Diuretics for Preventing and Treating Acute Kidney Injury. — Hashimoto H, Yamada H, Murata M, Watanabe N. The Cochrane Database of Systematic Reviews. 2025.
5. Acute Renal Failure. — Thadhani R, Pascual M, Bonventre JV. The New England Journal of Medicine. 1996.
6. Normotensive Ischemic Acute Renal Failure. — Abuelo JG. The New England Journal of Medicine. 2007.
7. The Primary Care Management of Chronic Kidney Disease (CKD) (2025). — Jonathan Casey Brown DO MPH, Wendy Caesar-Gibbs RD, Cynthia Delgado MD FASN FNKF, et al Department of Veterans Affairs. 2025.
8. ACR Manual on Contrast Media 2025. — ACR Committee on Drugs and Contrast Media American College of Radiology. 2025.
9. Extracorporeal Kidney-Replacement Therapy for Acute Kidney Injury. — Gaudry S, Palevsky PM, Dreyfuss D. The New England Journal of Medicine. 2022.
10. Acute Renal Failure. — Lameire N, Van Biesen W, Vanholder R. Lancet. 2005.
11. Drug-Induced Acute Kidney Injury: Diverse Mechanisms of Tubular Injury. — Perazella MA. Current Opinion in Critical Care. 2019.
12. Mechanisms of Antimicrobial-Induced Nephrotoxicity in Children. — Downes KJ, Hayes M, Fitzgerald JC, et al. The Journal of Antimicrobial Chemotherapy. 2020.
13. Acute Kidney Injury in Patients with Cirrhosis. — Nadim MK, Garcia-Tsao G. The New England Journal of Medicine. 2023.
14. Acute Kidney Injury in Patients with Cancer. — Rosner MH, Perazella MA. The New England Journal of Medicine. 2017.
15. Nephrotoxin Exposure and Acute Kidney Injury in Adults. — Griffin BR, Wendt L, Vaughan-Sarrazin M, et al. Clinical Journal of the American Society of Nephrology : CJASN. 2023.
16. Contemporary Management of Severe Acute Kidney Injury and Refractory Cardiorenal Syndrome: JACC Council Perspectives. — Jentzer JC, Bihorac A, Brusca SB, et al. Journal of the American College of Cardiology. 2020.
17. Updates in Management and Timing of Dialysis in Acute Kidney Injury. — Yu MK, Kamal F, Chertow GM. Journal of Hospital Medicine. 2019.
18. Diagnosis and Treatment of Acute Tubular Necrosis. — Esson ML, Schrier RW. Annals of Internal Medicine. 2002.
19. Renal Recovery After Severe Acute Renal Injury. — Schiffl H. European Journal of Medical Research. 2008.
20. Acute Kidney Injury. — Ostermann M, Lumlertgul N, Jeong R, et al. Lancet. 2025.
21. Long-Term Outcome of Acute Tubular Necrosis: A Contribution to Its Natural History. — Liaño F, Felipe C, Tenorio MT, et al. Kidney International. 2007.
22. Fenoldopam for Preventing and Treating Acute Kidney Injury. — Esezobor CI, Bhatt GC, Effa EE, Hodson EM. The Cochrane Database of Systematic Reviews. 2024.
23. Management of Acute Kidney Injury/Renal Replacement Therapy in the Intensive Care Unit. — Shaikhouni S, Yessayan L. The Surgical Clinics of North America. 2022.
24. Rhabdomyolysis and Acute Kidney Injury. — Bosch X, Poch E, Grau JM. The New England Journal of Medicine. 2009.
25. Differential Diagnosis of Acute Renal Failure. — Espinel CH, Gregory AW. Clinical Nephrology. 1980.
26. Diagnosis, Evaluation, and Management of Ascites, Spontaneous Bacterial Peritonitis and Hepatorenal Syndrome: 2021 Practice Guidance by the American Association for the Study of Liver Diseases. — Biggins SW, Angeli P, Garcia-Tsao G, et al. Hepatology. 2021.
27. Diagnostic Performance of Fractional Excretion of Sodium for the Differential Diagnosis of Acute Kidney Injury: A Systematic Review and Meta-Analysis. — Abdelhafez M, Nayfeh T, Atieh A, et al. Clinical Journal of the American Society of Nephrology : CJASN. 2022.
28. Evaluation of Simple Diagnostic Parameters in Acute Kidney Injury in Hospitalized Patients-Diagnostic Recommendations for Non-Nephrologists. — Buckenmayer A, Siebler N, Haas CS. Internal and Emergency Medicine. 2023.
29. Urinary Diagnostic Indices in Acute Renal Failure: A Prospective Study. — Miller TR, Anderson RJ, Linas SL, et al. Annals of Internal Medicine. 1978.
30. Renal Recovery From Acute Tubular Necrosis Requiring Renal Replacement Therapy: A Prospective Study in Critically Ill Patients. — Schiffl H. Nephrology, Dialysis, Transplantation : Official Publication of the European Dialysis and Transplant Association - European Renal Association. 2006.
31. Timing of Initiation of Renal-Replacement Therapy in Acute Kidney Injury. — STARRT-AKI Investigators, Canadian Critical Care Trials Group, Australian and New Zealand Intensive Care Society Clinical Trials Group, et al. The New England Journal of Medicine. 2020.
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Reviewed by Dr. Lucas Mastropaolo. SymptomDx is an educational tool for medical professionals — it does not replace clinical judgment. Verify all clinical data and drug dosages with authoritative sources.