Acute Kidney Injury — Evaluation & Management

Key Points

• Confirm AKI using creatinine trend, urine output, or both and determine the best available baseline.
• Ask whether the kidney problem is hemodynamic, intrinsic, obstructive, or mixed.
• Urinalysis and urine microscopy often provide more diagnostic value than reflex fractional excretion calculations.
• Use isotonic fluid for true hypovolemia, but stop escalating fluid when congestion develops or response is absent.
• Review nephrotoxins, renal dosing, contrast exposure, and medications that alter renal hemodynamics.
• Exclude obstruction early when risk factors or unexplained oliguria are present.
• Dialysis is indicated for refractory complications, not for a creatinine threshold alone.
• Every patient with significant AKI needs a recovery plan and reassessment for CKD after discharge.

Algorithm

1. Confirm the creatinine and urine-output abnormality and compare with prior kidney function.
2. Assess hemodynamics, volume status, sepsis, heart failure, medication exposure, recent procedures, and urinary symptoms.
3. Obtain urinalysis with microscopy, electrolytes, CBC, and cause-directed tests; use renal ultrasound or bladder assessment when obstruction is possible.
4. Restore perfusion if hypovolemic and treat shock while avoiding unnecessary chloride and fluid burden.
5. Stop or adjust nephrotoxic and renally cleared medications and relieve obstruction when present.
6. Monitor potassium, bicarbonate, fluid balance, urine output, and signs of uremia; treat complications promptly.
7. Consult nephrology for rapidly progressive, stage 3, unexplained, glomerular, or refractory AKI and evaluate kidney replacement therapy indications.
8. Plan repeat kidney function, medication restart decisions, blood pressure review, and CKD surveillance after recovery.

Clinical Synopsis & Reasoning

AKI is a syndrome rather than a single diagnosis. Current KDIGO criteria retain the core functional definition of an increase in serum creatinine of at least 0.3 mg/dL within 48 hours, an increase to at least 1.5 times baseline within 7 days, or sustained oliguria below 0.5 mL/kg/hour for at least 6 hours. A 2026 KDIGO update remains in public-review form as of August 2026, so final recommendations should be checked when formally published. Classify the likely cause as hemodynamic or prerenal, intrinsic renal, postrenal, or mixed. Common hemodynamic causes include volume depletion, sepsis, heart failure, and medication-related reduction in glomerular perfusion. Intrinsic causes include acute tubular injury, glomerulonephritis, interstitial nephritis, vascular disease, and pigment nephropathy. Obstruction must be considered early, especially in older men, pelvic malignancy, solitary kidney, urinary retention, or anuria. Examine for hypovolemia, congestion, rash, arthritis, edema, bladder distention, and systemic disease. Urinalysis with microscopy can provide high-value clues, such as muddy brown casts in tubular injury, dysmorphic erythrocytes or RBC casts in glomerulonephritis, pyuria in interstitial or infectious disease, and heme-positive urine with few RBCs in rhabdomyolysis. Fractional excretion indices can be supportive in selected cases but are not definitive, particularly after diuretics or in sepsis. Review all medications and recent contrast, procedures, infections, and hypotensive episodes.

Treatment Strategy & Disposition

Treat the cause and the complications rather than the creatinine number. Restore effective circulating volume with isotonic crystalloid when true hypovolemia is present, but avoid ongoing fluid administration once congestion or lack of fluid responsiveness emerges. In septic shock, follow sepsis hemodynamic principles. Stop or dose-adjust nephrotoxic and renally cleared drugs when appropriate, including NSAIDs and medications that accumulate dangerously in reduced GFR. RAAS inhibitors and SGLT2 inhibitors may need temporary interruption in selected acutely unstable patients, but long-term kidney and cardiovascular benefits should be considered when deciding when to restart them. Relieve urinary obstruction urgently when infection, severe renal dysfunction, solitary kidney, or bilateral obstruction is present. Manage hyperkalemia, severe acidosis, pulmonary edema, and uremic complications promptly. Loop diuretics do not treat intrinsic AKI and should not be used to force recovery, but they are appropriate for clinically important volume overload when the patient can respond. Kidney replacement therapy should be based on refractory complications and the overall clinical context, not on creatinine or BUN alone. Classic triggers include refractory acidosis, dangerous electrolyte disturbance, certain dialyzable intoxications, refractory pulmonary edema or volume overload, and symptomatic uremia. Arrange nephrology consultation for severe or progressive AKI, unclear intrinsic disease, suspected glomerulonephritis, refractory complications, or dialysis consideration. Survivors need post-AKI follow-up because CKD and recurrent AKI risk remain elevated even when creatinine appears to normalize.

Epidemiology / Risk Factors

• AKI is common in hospitalized and critically ill adults and frequently coexists with sepsis, surgery, heart failure, and exposure to nephrotoxic medications.
• Older age, CKD, diabetes, cirrhosis, malignancy, and prior AKI increase susceptibility.
• AKI may be community acquired or develop during hospitalization, and multiple mechanisms often coexist.
• Even apparently reversible AKI increases later risk of CKD, cardiovascular events, and death.
• Medication-related and hemodynamic contributors are common and potentially modifiable.

Investigations

AEIOU - Dialysis Triggers

Pharmacology

Prognosis / Complications

• Prognosis depends on AKI severity, duration, baseline CKD, critical illness, and whether the underlying cause can be reversed.
• Persistent oliguria and multiorgan failure identify higher-risk disease.
• Recovery may be complete, partial, or followed by acute kidney disease and CKD.
• Patients who require dialysis during AKI may later recover enough kidney function to discontinue it, so reassessment is essential.
• A documented post-AKI follow-up plan reduces the risk that persistent kidney dysfunction or medication errors are missed.

Patient Education / Counseling

• Review medications that can worsen kidney function during dehydration or acute illness and give individualized sick-day instructions.
• Avoid nonprescribed NSAIDs unless a clinician specifically recommends them.
• Seek urgent care for markedly reduced urine output, worsening swelling or breathlessness, confusion, persistent vomiting, or weakness suggestive of severe electrolyte disturbance.
• Arrange repeat creatinine, potassium, blood pressure, and urine testing after significant AKI.
• Explain that kidney recovery can continue after discharge and that medications stopped during AKI may need to be restarted deliberately rather than abandoned indefinitely.

Notes

The most common management error in AKI is treating an abnormal creatinine without identifying the physiology behind it. A dehydrated patient may improve with fluid, while a congested patient with cardiorenal syndrome may worsen. Similarly, a patient with glomerulonephritis can have a low fractional excretion of sodium and be harmed by repeated empiric fluid boluses. Reassessment should therefore follow every major intervention. Document baseline kidney function, likely cause, urine output, volume status, medication changes, and the plan for repeat laboratory testing. The 2026 KDIGO AKI/AKD guideline is still a public-review draft as of August 2026, so final publication should be checked before treating draft recommendations as definitive guidance.

References

1. KDIGO Acute Kidney Injury and Acute Kidney Disease Guideline Resources — Link