kdigo-aki-staging

name	kdigo-aki-staging
description	Calculate KDIGO AKI (Acute Kidney Injury) staging for ICU patients using creatinine and urine output criteria. Use for nephrology research, AKI outcome studies, or renal function monitoring.
tier	validated
category	clinical

KDIGO AKI Staging

The Kidney Disease: Improving Global Outcomes (KDIGO) criteria define Acute Kidney Injury (AKI) stages based on serum creatinine changes and/or urine output reduction.

When to Use This Skill

• AKI incidence and outcome studies
• Renal function trajectory analysis
• CRRT initiation studies
• Drug-induced nephrotoxicity research
• ICU quality metrics

AKI Staging Criteria

Creatinine-Based Criteria

Stage	Creatinine Criterion
1	>= 1.5x baseline within 7 days OR >= 0.3 mg/dL increase within 48h
2	>= 2.0x baseline
3	>= 3.0x baseline OR >= 4.0 mg/dL with acute increase OR RRT initiation

Urine Output-Based Criteria

Stage	Urine Output Criterion
1	< 0.5 mL/kg/h for 6-12 hours
2	< 0.5 mL/kg/h for >= 12 hours
3	< 0.3 mL/kg/h for >= 24 hours OR anuria for >= 12 hours

Final AKI Stage = MAX(creatinine stage, urine output stage, CRRT stage)

Pre-computed Tables

KDIGO Stages (Combined)

SELECT
    subject_id,
    hadm_id,
    stay_id,
    charttime,
    -- Creatinine criteria
    creat_low_past_7day,
    creat_low_past_48hr,
    creat,
    aki_stage_creat,
    -- Urine output criteria
    uo_rt_6hr,
    uo_rt_12hr,
    uo_rt_24hr,
    aki_stage_uo,
    -- CRRT
    aki_stage_crrt,
    -- Final stage
    aki_stage,
    aki_stage_smoothed  -- Smoothed over 6-hour window
FROM mimiciv_derived.kdigo_stages;

Creatinine with Baseline

SELECT
    hadm_id,
    charttime,
    creat,
    creat_low_past_7day,
    creat_low_past_48hr
FROM mimiciv_derived.kdigo_creatinine;

Urine Output Rates

SELECT
    stay_id,
    charttime,
    weight,
    uo_rt_6hr,   -- mL/kg/h over 6 hours
    uo_rt_12hr,  -- mL/kg/h over 12 hours
    uo_rt_24hr   -- mL/kg/h over 24 hours
FROM mimiciv_derived.kdigo_uo;

Critical Implementation Notes

1. Baseline Creatinine: Uses the lowest creatinine in the past 7 days as the baseline. This may underestimate AKI if patient was already in AKI on admission.

2. 48-Hour Window: The >= 0.3 mg/dL acute increase criterion uses the lowest creatinine in the past 48 hours specifically.

3. Stage 3 with Cr >= 4.0: Requires EITHER:

   • An acute increase >= 0.3 mg/dL within 48h, OR
   • An increase >= 1.5x baseline

4. Urine Output Timing: UO criteria require the patient to be in ICU for at least 6 hours before staging (KDIGO definition). Earlier times get stage 0.

5. Weight for UO Calculation: Uses documented weight from mimiciv_derived.kdigo_uo. Weight estimation methods vary.

6. CRRT as Stage 3: Any patient on CRRT is automatically Stage 3 AKI.

7. Smoothed Stage: aki_stage_smoothed carries forward the maximum stage from the past 6 hours to reduce fluctuation between creatinine/UO measurements.

8. Time Series Data: AKI is calculated at every creatinine/UO measurement time, not just once per admission.

Example: AKI Incidence

WITH max_aki AS (
    SELECT
        stay_id,
        MAX(aki_stage) AS max_aki_stage
    FROM mimiciv_derived.kdigo_stages
    GROUP BY stay_id
)
SELECT
    max_aki_stage,
    COUNT(*) AS n_stays,
    ROUND(100.0 * COUNT(*) / SUM(COUNT(*)) OVER(), 1) AS pct
FROM max_aki
GROUP BY max_aki_stage
ORDER BY max_aki_stage;

Example: AKI by Criteria Type

WITH aki_type AS (
    SELECT
        stay_id,
        MAX(aki_stage_creat) AS max_cr_stage,
        MAX(aki_stage_uo) AS max_uo_stage,
        MAX(COALESCE(aki_stage_crrt, 0)) AS max_crrt_stage
    FROM mimiciv_derived.kdigo_stages
    GROUP BY stay_id
)
SELECT
    CASE
        WHEN max_cr_stage > 0 AND max_uo_stage > 0 THEN 'Both Cr and UO'
        WHEN max_cr_stage > 0 THEN 'Cr only'
        WHEN max_uo_stage > 0 THEN 'UO only'
        WHEN max_crrt_stage > 0 THEN 'CRRT only'
        ELSE 'No AKI'
    END AS aki_type,
    COUNT(*) AS n_stays
FROM aki_type
GROUP BY 1;

Example: Time to AKI Development

WITH first_aki AS (
    SELECT
        k.stay_id,
        MIN(k.charttime) AS first_aki_time
    FROM mimiciv_derived.kdigo_stages k
    WHERE k.aki_stage >= 1
    GROUP BY k.stay_id
)
SELECT
    ROUND(
        TIMESTAMP_DIFF(f.first_aki_time, ie.intime, HOUR), 0
    ) AS hours_to_aki,
    COUNT(*) AS n_stays
FROM first_aki f
INNER JOIN mimiciv_icu.icustays ie ON f.stay_id = ie.stay_id
GROUP BY 1
HAVING hours_to_aki BETWEEN 0 AND 168  -- First week
ORDER BY 1;

Example: AKI Stage Transitions

WITH aki_trajectory AS (
    SELECT
        stay_id,
        charttime,
        aki_stage,
        LAG(aki_stage) OVER (PARTITION BY stay_id ORDER BY charttime) AS prev_stage
    FROM mimiciv_derived.kdigo_stages
    WHERE aki_stage IS NOT NULL
)
SELECT
    prev_stage AS from_stage,
    aki_stage AS to_stage,
    COUNT(*) AS n_transitions
FROM aki_trajectory
WHERE prev_stage IS NOT NULL
    AND prev_stage != aki_stage
GROUP BY 1, 2
ORDER BY 1, 2;

References

• KDIGO Clinical Practice Guideline for Acute Kidney Injury. Kidney International Supplements. 2012;2(1):1-138.
• Kellum JA, Lameire N. "Diagnosis, evaluation, and management of acute kidney injury: a KDIGO summary." Critical Care. 2013;17(1):204.