ACUTE KIDNEY INJURY

✓ Medically ReviewedDISEASEID: MDBT0073🚨 TRIAGE: EMERGENCYICD-10: N17

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Definition

CLINICAL DEFINITION

Acute Kidney Injury is sudden kidney dysfunction over hours to 7 days. It is defined by KDIGO (kidney disease improving global outcomes) creatinine (blood waste chemical) or urine criteria. Criteria include creatinine rise of 0.3 mg per dL within 48 hours. They include 1.5-fold rise from baseline within 7 days. They include urine under 0.5 mL per kg per hour for 6 hours.

IN PLAIN ENGLISH

Acute Kidney Injury means kidneys suddenly stop filtering well. Kidneys normally remove waste and balance fluids and salts. In AKI waste builds up and urine may fall. It often follows severe illness, dehydration (low body fluid) or blocked urine flow.

COMMON MISCONCEPTION / WHAT IT DOES NOT MEAN

Acute Kidney Injury is not chronic kidney disease (long term gradual kidney loss). It is not stable mildly high creatinine (blood waste marker) without acute change. It is not simple dehydration (low fluid) that corrects instantly without kidney injury. It is not chronic dialysis dependence without new acute worsening.

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Word Breakdown

acute-

=sudden or sharp in onset

kidney

=kidney, the blood filtering organ

Literal Meaning: sudden kidney damage

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Abbreviations

AKI=Acute Kidney Injury - sudden fall in kidney filtering over hours to days

ARF=Acute Renal Failure - older term for AKI, now replaced by AKI staging

AKD=Acute Kidney Disease - dysfunction persisting 7 to 90 days after AKI

ATN=Acute Tubular Necrosis - common intrinsic AKI pattern with tubule cell injury

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Synonyms & Variants

Acute renal failure›Acute kidney failure›Acute renal insufficiency›

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Category-Specific Context

Acute Kidney Injury is a Disease because it is a pathological process with causes and stages. It is not a single Symptom (patient complaint) or Sign (exam finding). It produces symptoms like oliguria (low urine) and signs like overload (fluid excess). Staging guides urgency, cause workup and dialysis planning.

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Clinical Context & Usage

CLINICAL SETTINGS

Emergency DepartmentIntensive Care UnitGeneral Medical WardPostoperative Recovery UnitNephrology Follow-up Clinic

USAGE & DOCUMENTATION NOTES

Use the term when KDIGO (kidney injury criteria) creatinine or urine thresholds are met. Always state stage, baseline creatinine (prior waste level) and suspected cause. Distinguish AKI from CKD (chronic kidney disease) and AKI on CKD (acute on chronic). Document urine output (hourly urine volume), fluids, nephrotoxins (kidney harming drugs) and obstruction check.

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Primary Causes & Pathophysiology

PATHOPHYSIOLOGY

Acute Kidney Injury reflects fall in glomerular filtration rate (kidney filtering rate). Prerenal (before kidney) means low perfusion (poor kidney blood flow) from volume loss or low pressure. Sustained ischaemia (oxygen lack) or toxins cause intrinsic injury like acute tubular necrosis (tubule cell death). Postrenal (after kidney) means obstruction (blocked urine flow) raises pressure and stops filtration. All pathways retain waste and disturb acids and salts.

PRIMARY CAUSES

Hypovolaemia from bleeding, vomiting, diarrhoea, burns or over-diuresis

Low circulating volume reduces renal perfusion (kidney blood flow). Filtration pressure falls and tubules suffer ischaemic stress.

Sepsis with hypotension and systemic vasodilation

Low vascular tone plus inflammatory mediators cut glomerular perfusion. Direct tubular injury follows from inflammation and microclots.

Heart failure, cardiogenic shock or cirrhosis with low effective perfusion

Low output or vessel widening activates hormones that tighten kidney vessels. Sodium retention rises while filtration falls.

Acute tubular necrosis from prolonged ischaemia

Prolonged oxygen lack kills tubular lining cells. Casts block tubules and delay filtration recovery.

Acute interstitial nephritis from infection or allergy

Immune cells invade the interstitium (tissue between tubules). Swelling and tubular dysfunction reduce filtration.

Glomerulonephritis and vasculitis

Glomerular (filter unit) inflammation and crescents block filtering surface. Blood and protein leak into urine.

Urinary tract obstruction from stones, prostate enlargement, tumour or clots

Blocked outflow raises pressure upstream. Rising pressure opposes filtration until it stops.

Rhabdomyolysis with myoglobin release

Myoglobin (muscle pigment) blocks tubules and causes oxidative injury. Vessel tightening worsens the damage.

Multiple myeloma with cast nephropathy

Excess light chains (myeloma proteins) block tubules with Tamm-Horsfall protein. Inflammation then injures surrounding tissue.

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Drug-Induced Causes

💊 Nonsteroidal anti-inflammatory drugs (NSAIDs) ↗

Mechanism: Block prostaglandin vessel widening and lower glomerular perfusion, mainly when volume is low

→ Stop NSAID, restore volume, watch creatinine and potassium, use safer pain relief

💊 ACE inhibitors and angiotensin receptor blockers ↗

Mechanism: Widen outflow vessels and drop filtration pressure when perfusion is low or renal arteries are narrow

→ Hold during AKI, low pressure or high potassium, recheck creatinine, restart only when stable

💊 Aminoglycosides ↗

Mechanism: Collect in proximal tubule cells and cause direct tubular toxicity with magnesium and potassium loss

→ Stop or switch antibiotic, check drug levels, hydrate, watch hearing and kidney function

💊 Vancomycin ↗

Mechanism: Causes oxidative tubular injury and interstitial inflammation, worse with high levels and combined nephrotoxins

→ Check levels, adjust or stop, hydrate, avoid pairing with aminoglycosides where possible

💊 Iodinated contrast media ↗

Mechanism: Causes inner kidney oxygen lack plus direct tubular toxicity, mainly with dehydration or CKD

→ Hydrate before and after, use lowest dose, avoid repeat studies, hold other nephrotoxins

💊 Cisplatin and other platinum chemotherapy ↗

Mechanism: Damages proximal tubule DNA and wastes magnesium, leading to tubular necrosis

→ Give saline hydration with magnesium, watch creatinine, hold or switch per oncology and nephrology

💊 Amphotericin B ↗

Mechanism: Forms pores in tubule membranes and tightens inflow vessels, causing potassium and magnesium loss

→ Use liposomal form if needed, give saline loading, replace salts, stop or switch antifungal

💊 Calcineurin inhibitors ciclosporin and tacrolimus ↗

Mechanism: Tighten inflow vessels and injure small arteries, lowering filtration

→ Check levels, reduce or switch only via transplant team, watch pressure and creatinine

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Epidemiology

Prevalence:Acute Kidney Injury is common in hospital and intensive care (critical care unit). Risk rises with age, frailty and comorbidity (other illnesses). It is frequent during sepsis (severe infection), major surgery and heart failure. Rates vary by case mix and creatinine (waste marker) surveillance.

Age Group:Acute Kidney Injury occurs at all ages from newborns to older adults. Older adults carry highest risk from CKD (chronic kidney disease), many drugs and vessel disease. Children usually develop it after dehydration (fluid loss), sepsis or glomerulonephritis (filter inflammation). Prematurity and critical illness raise neonatal risk.

Geographic Distribution:Acute Kidney Injury occurs worldwide in all health systems. Infection and volume loss dominate in some regions and seasons. Postoperative, contrast (dye related) and drug related cases dominate in hospital cohorts. Outcomes track access to fluids, monitoring and dialysis (artificial kidney support).

Red Flags & Triage ★

TRIAGE LEVEL

🚨 EMERGENCY

DO NOT MISS — LIFE-THREATENING PRESENTATIONS

Hyperkalaemia with ECG changes
Urinary obstruction needing urgent relief
Severe sepsis and hypotension driving ischaemia
Glomerulonephritis or vasculitis needing immunosuppression
Rhabdomyolysis and tumour lysis with toxin load
Drug induced AKI needing drug hold

URGENT EVALUATION TRIGGERS

Anuria or severe oliguria under 100 mL per day
Potassium above 6 or ECG peaking or widening
Severe acidosis with fast deep breathing or confusion
Pulmonary oedema with low oxygen despite diuretics
Uraemic confusion, pericardial rub or bleeding
Suspected obstruction with pain and hydronephrosis

Contraindications & Precautions

SPECIAL PRECAUTIONS

Avoid NSAIDs, aminoglycosides and other nephrotoxins during AKI
Adjust renally cleared drug doses and watch levels
Track fluid balance, daily weight and lung signs closely
Recheck creatinine, salts and acid base often
Relieve obstruction promptly and avoid prolonged low pressure

Complications

DOWNSTREAM CLINICAL COMPLICATIONS

Hyperkalaemia (high potassium) with arrhythmia risk
Metabolic acidosis (acid build-up)
Fluid overload with pulmonary oedema (lung fluid)
Hypertension (high blood pressure)
Uraemic encephalopathy (brain dysfunction) and pericarditis
Bleeding from platelet dysfunction
Infection and poor wound healing
Progression to chronic kidney disease
Need for acute dialysis

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Confused With (LASA & DDx) ★

LEXICAL (LASA) — SIMILAR NAMES

Chronic Kidney Disease

Shares kidney disease wording and high creatinine, but it is long term irreversible loss with small kidneys and anaemia, not sudden injury

Acute Kidney Disease

Overlaps in timing and sounds identical, but it is persistent dysfunction 7 to 90 days after AKI, not the first 7-day injury

Acute tubular necrosis

Often used interchangeably with AKI, but it is one intrinsic subtype with muddy brown casts, not the whole prerenal plus intrinsic plus postrenal syndrome

CLINICAL DIFFERENTIAL DIAGNOSES (DDx)

Chronic Kidney Disease

Key Distinguishing Feature: Stable high creatinine over months with small bright kidneys and anaemia without acute trigger

AKI on Chronic Kidney Disease

Key Distinguishing Feature: Acute creatinine jump above known abnormal baseline with recent insult plus chronic stigmata

Volume-responsive azotaemia without established injury

Key Distinguishing Feature: Rapid creatinine fall within 24 to 48 hours of fluids with bland urine

Acute glomerulonephritis with rapidly progressive course

Key Distinguishing Feature: Active urine sediment with red cell casts and proteinuria plus hypertension and oedema

Urinary obstruction

Key Distinguishing Feature: Anuria or fluctuating output with hydronephrosis (swollen drainage) on ultrasound, relieved by catheter or stent

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Clinical Pearls

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Compare to baseline creatinine within 7 days and 3 months to separate AKI from CKD and AKI on CKD.

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Bladder scan and renal ultrasound early when output falls to avoid missing obstruction that needs relief.

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Check urine sediment and protein to spot glomerulonephritis or interstitial nephritis that needs specific therapy.

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Hold NSAIDs, ACE inhibitors and other nephrotoxins during low pressure and review all renally cleared doses.

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Dialyse for refractory high potassium, acidosis, overload, uraemic pericarditis or encephalopathy, not creatinine alone.

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Example Usage & SOAP

CLINICAL SENTENCE

""70-year-old with pneumonia developed oliguria and creatinine rise from acute kidney injury.""

IN A SOAP NOTE

S: 68-year-old with fever, vomiting and very low urine for 2 days, no chest pain. O: Temp 38.2C, BP 92/58, HR 112, RR 22, SpO2 94 percent on air, crackles present, urine 120 mL in 12 hours, creatinine 2.8 mg per dL from baseline 1.0, potassium 5.8, bicarbonate 16. A: Sepsis with AKI stage 3, oliguria, high potassium and metabolic acidosis. P: Fluids with reassessment, broad antibiotics, hold NSAIDs and ACE inhibitor, bladder scan plus renal ultrasound, strict balance and nephrology referral, prepare for dialysis if no improvement.

DIFFERENTIAL DIAGNOSIS CONTEXT

Stable high creatinine with small kidneys favours CKD (chronic gradual loss). Sudden jump within days after sepsis (severe infection), low pressure or nephrotoxin (kidney harming drug) favours AKI. Acute rise above known abnormal baseline favours AKI on CKD (acute on chronic). Old labs, urinalysis (urine test) and ultrasound (kidney imaging) separate them.

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Classifications & Scoring

STAGING SCALE

KDIGO AKI Staging

Stage 1 is creatinine 1.5 to 1.9 times baseline or 0.3 mg per dL rise or urine under 0.5 mL per kg per hour for 6 to 12 hours. Stage 2 is creatinine 2.0 to 2.9 times baseline or urine under 0.5 for over 12 hours. Stage 3 is creatinine 3 times baseline or over 4.0 mg per dL or dialysis started or urine under 0.3 for 24 hours or anuria over 12 hours.

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Prognosis

SHORT-TERM OUTCOME

Short term outcome follows cause, stage and comorbidity (other diseases). Many mild cases recover within days after perfusion (blood flow) returns. Severe AKI with oliguria (low urine), acidosis (acid excess) or multiorgan failure carries high mortality. Dialysis (machine kidney support) need marks higher risk and longer stay.

LONG-TERM PROGNOSIS

Many survivors do not fully regain baseline filtering. Acute Kidney Injury raises later risk of CKD (chronic kidney disease), hypertension (high pressure) and cardiovascular (heart and vessel) events. Repeat episodes speed decline toward dialysis dependence. Long term checks of creatinine (waste marker), proteinuria (urine protein) and pressure are needed.

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References & Coding

ICD-10 DIAGNOSTIC CODE

N17

LITERATURE CITATIONS & GUIDELINES

[1]WHO ICD-10 N17

[2]KDIGO Acute Kidney Injury Guideline

[3]NICE Acute kidney injury guideline

MEDICAL DISCLAIMER — This content is intended for educational purposes and qualified healthcare professionals only. Always refer to current clinical diagnostic criteria, institutional protocols, and official guidelines. Medobo is not responsible for clinical decisions made based on this content.