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Acute Kidney Injury — KDIGO Staging, Prerenal vs Intrinsic vs Postrenal, and Nephrotoxins

System: Internal Medicine • Reviewed: Sep 2, 2025 • Step 1Step 2Step 3

Synopsis:

AKI is an abrupt decline in kidney function. Identify prerenal, intrinsic, and postrenal causes using history, exam, labs, and ultrasound; stage using KDIGO criteria; stop nephrotoxins; optimize hemodynamics; and involve nephrology for refractory complications or RRT indications.

Key Points

  • Use the highest‑yield diagnostic test early; do not let testing delay time‑critical therapy.
  • Set objective targets and reassess frequently.
  • Plan definitive source control or disease‑specific therapy when indicated; document follow‑up and patient education.

Algorithm

  1. Confirm AKI and stage with KDIGO; review meds and exposures; assess volume status.
  2. Differentiate prerenal vs intrinsic vs postrenal with UA/sediment, indices, and ultrasound.
  3. Treat cause; manage complications (K+, acidosis, volume); call nephrology for RRT indications (AEIOU).

Clinical Synopsis & Reasoning

AKI is an abrupt decline in kidney function. Identify prerenal, intrinsic, and postrenal causes using history, exam, labs, and ultrasound; stage using KDIGO criteria; stop nephrotoxins; optimize hemodynamics; and involve nephrology for refractory complications or RRT indications.


Treatment Strategy & Disposition

Stabilize ABCs. Initiate guideline‑concordant first‑line therapy with precise dosing and continuous monitoring. Escalate to advanced/procedural interventions based on explicit failure criteria. Define ICU, step‑down, and ward disposition triggers; involve specialty teams early.


Epidemiology / Risk Factors

  • Risk varies by comorbidity and precipitants; see citations for condition‑specific data.

Investigations

TestRole / RationaleTypical FindingsNotes
Urinalysis with sediment and FeNa/FeUreaEtiologyPrerenal vs ATN vs GNCasts guide diagnosis
Renal ultrasoundPostrenalHydronephrosisQuick screen
Daily weights, I/O, and medication reviewManagementVolume and nephrotoxinsTitrate fluids/diuretics

High-Risk & Disposition Triggers

TriggerWhy it mattersAction
Refractory hyperkalemia/pulmonary edema/uremiaDialysis indicationUrgent RRT
Rapid Cr rise or anuriaProgressionNephrology consult

Pharmacology

Medication/InterventionMechanismOnsetRole in TherapyLimitations
Balanced crystalloids for prerenal statesFluidsHoursRestore perfusionAvoid overload
Diuretics for volume overloadDiureticHoursSymptom controlDoes not treat ATN per se
Immunosuppression for GN (selected)Disease-modifyingDays-weeksCondition-specificSpecialist guided

Prognosis / Complications

  • Outcome depends on timeliness of diagnosis and definitive therapy; monitor for complications.

Patient Education / Counseling

  • Provide red‑flag education, adherence guidance, and explicit return precautions; arrange timely specialty follow‑up.

References

  1. KDIGO AKI guideline — Link

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