Epidemiology of Acute Kidney Injury

1. Definitions and Diagnostic Challenges

• Many studies use billing/diagnostic codes (e.g., ICD-9/ICD-10), which have poor sensitivity - one large VA study found only 49% of creatinine-confirmed AKI had an associated AKI billing code.
• Serum creatinine is only measured during health encounters, introducing ascertainment bias.
• The urine output criterion is relatively recent and inconsistently captured.
• There is no uniform definition for the cause of AKI in large databases.

2. Incidence

Community-Based Incidence

• Northern California: 522.4 cases/100,000 person-years (all AKI); 29.5 cases/100,000 person-years for dialysis-requiring AKI.
• Scotland: 214.7 cases/100,000 patient-years (all AKI); 18.3 cases/100,000 for dialysis-requiring AKI.
• Canadian cohorts: rates varied enormously - 100 to 11,700 cases/100,000 person-years depending on baseline GFR and proteinuria, demonstrating the huge impact of underlying CKD on susceptibility.
• Among Medicare beneficiaries >65 years: 4.0% had an AKI-coded hospitalization in 1 year.

Hospital-Based Incidence

• A worldwide meta-analysis estimated nearly 25% of hospitalized patients had AKI by the KDIGO definition, with approximately 10% requiring kidney replacement therapy (KRT).
• This estimate is echoed in the ISN global initiative, which cites the same ~25% figure as a call to action to eliminate preventable AKI deaths by 2025.

AKI After Major Surgery (7-day incidence)

Community-Acquired vs. Hospital-Acquired AKI

3. Outcomes

• CKD development and progression: The incidence of CKD, eGFR decline, ESKD, and death are all higher after AKI, with risk graded by AKI stage.
• ESKD risk: In one U.S. study, surviving a dialysis-requiring AKI episode was associated with a 2.8x higher risk of progressing to stage G4/G5 CKD.
• Mortality: Even modest creatinine rises confer increased risk. Oliguria alone, even without a rise meeting AKI criteria, may confer higher risk.
• Economic burden: A 2005 study found a serum creatinine rise ≥0.5 mg/dL was associated with 3.5 extra hospital days and $7,500 in excess costs per patient.
• Non-recovery: Many patients with KRT-requiring AKI never recover full kidney function.
• Debate remains over whether adverse outcomes are caused by AKI or simply reflect shared risk factors - no interventional trial has definitively proven causation.

4. Risk Factors

Patient-Level Risk Factors

• Older age - the single strongest demographic predictor
• Male sex
• Black race - though this may be confounded by socioeconomic disparities; not fully explained by APOL1 risk variants in limited studies
• Diabetes mellitus - 1.5- to 2.5-fold increased odds of AKI
• Pre-existing CKD (lower eGFR) - the strongest modifiable risk factor, in a graded dose-response relationship
• Proteinuria/albuminuria - also confers graded increased risk, independent of eGFR
• Hypertension

Setting-Specific and Exposure-Based Risk Factors

• Sepsis - the leading cause of AKI in the ICU; sepsis-associated AKI accounts for the majority of ICU AKI cases (multicenter AKI-EPI data)
• Cardiac surgery / cardiopulmonary bypass
• Major non-cardiac surgery
• Nephrotoxic drugs - aminoglycosides, NSAIDs, contrast media, cisplatin
• Volume depletion / haemorrhage
• Liver failure (hepatorenal syndrome)
• Immune checkpoint inhibitor therapy (emerging cause; ASCO/ASNO position statement 2025)

5. Special Populations

• Neonates: A 2024 meta-analysis in Pediatrics (PMID 38872621) found AKI is common in neonatal ICUs, especially in very preterm infants; incidence varies widely by definition used.
• ICU patients: A multinational ICU study (AKI-EPI) and Finnish FINNAKI study found AKI in 50-60% of ICU patients, with 90-day mortality exceeding 40% in severe stages.
• Cirrhosis: AKI (including hepatorenal syndrome) is extremely common in hospitalised cirrhotic patients, with significantly worse outcomes than AKI in other settings (Patidar et al., J Hepatol 2023).
• Older adults (>65 years): Carry disproportionate burden; incidence of dialysis-requiring ESKD in this group increased from 1,203 to 1,556 cases/million between 1996 and 2014.

6. Global Burden and Disparities

• The ISN Global Snapshot and other global initiatives highlight enormous geographic disparities in AKI detection and treatment access.
• High-income countries have better surveillance and KRT access; many AKI deaths in low- and middle-income countries go unrecorded due to absence of creatinine testing or dialysis services.
• The ISN set a goal to eliminate preventable deaths from AKI by 2025 - largely unmet due to infrastructure gaps in the developing world.

Summary Table

Epidemiology of AKI

• Community: ~215–522 cases/100,000 person-years
• Hospitalized patients: ~25% develop AKI (KDIGO criteria)
• ICU: 40–60%
• ~10% of hospitalized AKI cases require dialysis

• Older age, male sex, diabetes, pre-existing CKD, albuminuria, sepsis, major surgery, nephrotoxins

• Survivors have 2.8x higher risk of CKD progression
• Even a 0.5 mg/dL creatinine rise = 3.5 extra hospital days + $7,500 excess cost
• Many KRT-requiring AKI patients never fully recover kidney function

• Massive treatment gap in low-income countries; ISN goal to eliminate preventable AKI deaths by 2025 largely unmet

AKI Epidemiology in Nepal

• Non-ICU hospital admissions: ~15%
• ICU patients: up to 60%
• No national surveillance data exists; true burden is likely underestimated

• Infections and sepsis (including tropical - malaria, dengue, leptospirosis)
• Diarrheal illness and severe dehydration
• Snakebite envenomation - especially in the Terai/southern lowlands; major cause of severe AKI requiring dialysis
• Obstetric complications - eclampsia, septic abortion
• Nephrotoxic traditional/herbal medicines (Ayurvedic preparations, including aristolochic acid)
• Acute post-streptococcal glomerulonephritis (children and adults)
• Chemical poisoning

• Dialysis access mainly in urban Kathmandu; nearly absent in rural areas
• Workforce shortage; patients often travel far to reach tertiary care
• No pharmacovigilance for nephrotoxic herbal remedies
• High out-of-pocket costs limit private care access

Epidemiology of AKI

Incidence

Community-Acquired vs. Hospital-Acquired

• Globally: ~2/3 community-acquired, 1/3 hospital-acquired
• Nepal: community-acquired AKI predominates - affects younger, previously healthy individuals who present late with advanced disease

Causes

• Global: sepsis, major surgery, nephrotoxic drugs, contrast, cardiac surgery
• Nepal (distinct pattern): infections/sepsis (malaria, dengue, leptospirosis), severe diarrheal dehydration, snakebite (Terai region), obstetric complications (eclampsia, septic abortion), nephrotoxic herbal/Ayurvedic medicines (aristolochic acid), post-streptococcal GN

Risk Factors

• Global: older age, male sex, diabetes, pre-existing CKD, albuminuria, low eGFR
• Nepal adds: rural residence, delayed presentation, poverty, use of traditional medicine, lack of early diagnostics

Outcomes

System-Level Gaps (Nepal-specific)

• No national AKI surveillance - true burden underestimated
• Dialysis facilities concentrated in Kathmandu; nearly absent rurally
• Workforce shortage; long travel to tertiary care
• No pharmacovigilance for nephrotoxic herbal remedies
• High out-of-pocket costs

Epidemiology of AKI

• Community: ~215–522 cases/100,000 person-years (Nepal: no national data; true burden underestimated)
• Hospitalized: ~25% globally; ~15% non-ICU in Nepal
• ICU: 40–60% globally and in Nepal
• ~10% require dialysis globally (Nepal: severely limited dialysis access outside Kathmandu)

• Older age, male sex, diabetes, pre-existing CKD, albuminuria, sepsis, major surgery, nephrotoxins
• Nepal adds: rural residence, delayed presentation, use of nephrotoxic herbal/Ayurvedic medicines, poverty

• Globally: sepsis, surgery, contrast, drugs
• Nepal: infections (malaria, dengue, leptospirosis), diarrheal dehydration, snakebite (Terai region), obstetric complications (eclampsia, septic abortion), aristolochic acid herbal remedies, post-streptococcal GN
• Most AKI in Nepal is community-acquired (unlike HIC where hospital-acquired dominates)

• Survivors have 2.8x higher CKD progression risk; even small creatinine rises = 3.5 extra days + $7,500 cost
• Nepal/South Asia: mortality ranges 2.2–52% (vs. much lower in HIC); complete recovery only 40–80% — reflecting late presentation and limited KRT access

• Massive treatment gap in LMICs; ISN goal to eliminate preventable AKI deaths by 2025 largely unmet
• Nepal: no national surveillance, dialysis concentrated in Kathmandu, high out-of-pocket costs — most preventable cases go unrecognized