Acute Kidney Injury — Diagnosis and Management

Key Points

• AKI is defined by change from baseline kidney function, not by a single abnormal creatinine value.
• Assess volume status and perfusion before giving fluid; congestion can worsen kidney function and pulmonary edema.
• Urinalysis and urine microscopy can substantially narrow the differential when interpreted with clinical context.
• Always consider postrenal obstruction because it is often rapidly reversible.
• Medication reconciliation and renal dose adjustment are core AKI treatments, not administrative details.
• Treat dangerous hyperkalemia, acidosis, pulmonary edema, and uremic complications immediately.
• Dialysis decisions are based on refractory complications and clinical trajectory, not an isolated creatinine threshold.
• Survivors need follow-up because an AKI episode increases future CKD and cardiovascular risk.

Algorithm

1. Confirm the creatinine trend and urine output, then compare with prior kidney function.
2. Assess airway, hemodynamics, perfusion, volume status, bladder distention, medications, and recent exposures.
3. Obtain electrolytes, bicarbonate, CBC, urinalysis with microscopy, and targeted tests for suspected causes.
4. Correct shock or true hypovolemia while avoiding fluid overload in congested patients.
5. Stop nephrotoxins, adjust renally cleared drugs, and relieve urinary obstruction when present.
6. Treat hyperkalemia, severe acidosis, pulmonary edema, or other life-threatening complications immediately.
7. Trend creatinine, potassium, urine output, weight, and fluid balance; involve nephrology for severe, progressive, or unclear AKI.
8. Arrange post-AKI kidney follow-up after discharge or recovery.

Clinical Synopsis & Reasoning

AKI is a syndrome rather than a single disease. Creatinine may lag behind the actual fall in glomerular filtration, and urine output can provide an earlier signal in critically ill patients. Compare the current creatinine with a reliable baseline whenever possible and review the time course. A small creatinine rise may be clinically important, especially in older adults, patients with chronic kidney disease, cirrhosis, heart failure, or sepsis. Oliguria should be confirmed with accurate intake and output measurement and assessment for catheter obstruction or retention before assuming intrinsic renal failure.

The differential is organized into prerenal, intrinsic, and postrenal mechanisms. Prerenal AKI reflects reduced effective renal perfusion from volume loss, sepsis, hemorrhage, heart failure, cirrhosis, or altered renal hemodynamics from medications. Intrinsic AKI includes acute tubular injury, glomerulonephritis, interstitial nephritis, vascular disease, pigment nephropathy, and toxin-mediated injury. Postrenal AKI results from obstruction and should be actively excluded when there is anuria, urinary retention, pelvic malignancy, stones, prostate disease, neurogenic bladder, or unexplained persistent AKI. More than one mechanism commonly coexists.

Urinalysis with microscopy is highly useful when interpreted in context. Granular casts support acute tubular injury, dysmorphic red cells or red-cell casts raise concern for glomerulonephritis, white-cell findings can occur with interstitial nephritis or infection, and heme-positive urine with few red cells suggests myoglobin or hemoglobin. Fractional excretion indices can be misleading after diuretics, in sepsis, glomerular disease, or chronic kidney disease and should not override the clinical picture. Renal ultrasound is appropriate when obstruction is plausible or the cause remains uncertain.

Treatment Strategy & Disposition

Stabilize hemodynamics and treat the cause. Give isotonic crystalloid when true intravascular depletion is present, but avoid reflexive fluid loading in patients with pulmonary edema, venous congestion, or cardiogenic physiology. In shock, restore perfusion with fluids and vasopressors according to the underlying syndrome. Stop or reduce nephrotoxins when possible, including NSAIDs, iodinated contrast when avoidable, aminoglycosides, and medications that accumulate dangerously as filtration falls. Renally dose antimicrobials, anticoagulants, insulin, gabapentinoids, and other cleared drugs.

Treat complications directly. Hyperkalemia with ECG changes or severe elevation requires immediate membrane stabilization with IV calcium followed by intracellular potassium shifting and definitive potassium removal. Severe metabolic acidosis, pulmonary edema, uremic encephalopathy or pericarditis, refractory hyperkalemia, and selected toxin exposures are classic indications for urgent kidney replacement therapy. Dialysis should not be triggered by creatinine alone. Conversely, a very high creatinine does not justify delay when a life-threatening complication is present.

Monitor creatinine, potassium, bicarbonate, fluid balance, blood pressure, and urine output serially. Early nephrology involvement is appropriate for stage 2 or 3 AKI, rapidly rising creatinine, persistent oliguria, suspected glomerulonephritis or vasculitis, unexplained AKI, transplant kidney dysfunction, or anticipated dialysis. After recovery, document the episode and arrange repeat kidney-function testing because AKI increases later risk of chronic kidney disease, cardiovascular events, recurrent AKI, and mortality.

Epidemiology / Risk Factors

• AKI is common among hospitalized and critically ill adults and often accompanies sepsis, surgery, shock, and major trauma.
• Older age, baseline CKD, diabetes, heart failure, cirrhosis, and nephrotoxic exposures increase risk.
• Hospital-acquired AKI is frequently multifactorial rather than attributable to a single insult.
• Even transient AKI is associated with higher subsequent CKD and cardiovascular risk.
• Recurrent AKI episodes compound long-term kidney risk.

Investigations

Common Etiologies by Category

Pharmacology

Prognosis / Complications

• Outcome depends on severity, cause, duration, baseline kidney reserve, and associated critical illness.
• Rapid reversal of hypoperfusion or obstruction can lead to near-complete recovery.
• Persistent stage 3 AKI, prolonged oliguria, multiorgan failure, or dialysis requirement is associated with worse prognosis.
• Some patients who require acute dialysis recover enough kidney function to stop it, while others progress to chronic kidney failure.
• Follow-up kidney testing is important even when creatinine appears to return to baseline.

Patient Education / Counseling

• Explain the suspected cause of the kidney injury and which medicines should be held or dose-adjusted temporarily.
• Avoid nonprescribed NSAIDs and dehydration during recovery unless a clinician has given a different plan.
• Review when to restart chronic blood-pressure or heart-failure medications that were held during the acute episode.
• Seek urgent care for markedly reduced urine, progressive swelling, dyspnea, weakness, palpitations, confusion, or persistent vomiting.
• Arrange repeat creatinine, electrolytes, blood pressure, and urine testing according to AKI severity and recovery.
• Patients with residual proteinuria, reduced eGFR, recurrent AKI, or uncertain cause should have kidney-focused follow-up.

Notes

Kidney replacement therapy is indicated for clinical problems such as refractory hyperkalemia, severe acidemia, pulmonary edema, selected intoxications, or symptomatic uremia rather than for a creatinine number alone.

AKI care should transition into recovery care. Medication reconciliation, blood-pressure reassessment, and repeat kidney testing reduce the chance that an acute event becomes an unrecognized chronic problem.

References

1. National Kidney Foundation KDOQI Guidelines — Link
2. KDIGO Acute Kidney Injury Guideline — Link