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Approach to acute kidney injury

The same eight steps, every presentation: threats first, then the history and exam that discriminate, one honest sentence, a mechanism-grouped differential, and the tests read in order.

  1. Immediate threats

    • Hyperkalemia with ECG changes
    • Refractory volume overload
    • Uremic encephalopathy or pericarditis
    • Severe acidosis

  2. History that discriminates

    • The trend: baseline creatinine, and when it left it
    • Intake, losses, and thirst; urine output honestly quantified
    • The medication interrogation: NSAIDs, RAAS blockade, diuretics, contrast, new antibiotics
    • Obstructive symptoms; systemic features (rash, arthralgia, fever)

  3. Examination

    • Volume status: JVP, orthostatics, edema, weight trend
    • Bladder scan on everyone
    • Skin: rash (interstitial nephritis, vasculitis), livedo

  4. Problem representation

    Oliguric creatinine rise after diarrheal losses on ramipril and naproxen (prerenal setup) versus AKI with a nephritic sediment and hemoptysis (pulmonary-renal emergency).

  5. Differential, by mechanism

    Prerenal

    • Volume depletion
    • Sepsis and vasodilation
    • Cardiorenal
    • Hepatorenal
    • RAAS/NSAID physiology

    Intrinsic

    • ATN (ischemic, toxic, pigment)
    • Glomerulonephritis
    • Interstitial nephritis
    • Vascular (vasculitis, TMA)

    Postrenal

    • Bladder outlet obstruction
    • Bilateral ureteric obstruction
    • Obstructed solitary kidney

  6. Investigations

    • Urinalysis with microscopy: the kidney's own biopsy-lite
    • Urine electrolytes (FENa, FEUrea on diuretics)
    • Bladder scan, then renal ultrasound
    • Targeted serologies when the sediment is nephritic

  7. Interpretation

    • FENa below 1 percent with bland sediment: intact tubules under hypoperfusion
    • Muddy brown casts: tubular injury
    • Red cell casts: glomerular inflammation, and a faster phone call

  8. Next steps

    • Stop the nephrotoxins and dose-adjust everything renally cleared
    • Match volume therapy to the examined volume state
    • Define dialysis triggers out loud before they are needed

Connected

AlgorithmWalk the pathwayLabsThe trend caseCaseAKI with teeth

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