Interactive physiology

AKI & CKD

Creatinine is a late, indirect marker of GFR: it rises only as it accumulates, so it trails the injury by days. Where the injury sits decides what the urine shows. CKD is staged by GFR and albuminuria together, and both set the risk.

Crss=Cr₀ 80 × GFR₀ 100GFR 10 =800 µmol/L
τ= Vd 42 LGFR 14.4 L/day =2.9 days
True GFReGFR from creatinineCreatinineKDIGO 123
Single-compartment model: creatinine made at a constant rate G, spread through total body water (Vd = 0.6 × weight) and cleared by GFR, so dCr/dt = (G − GFR × Cr) / Vd. eGFR is CKD-EPI 2021 for a 55-year-old man, applied to each day's creatinine as a laboratory would. Faint lines show the whole course.
Step 5 of 5 Recovery day 8

90%
70 kg · 42 L
Steady-state map. The curve is where creatinine settles for each GFR (Cr = G / GFR), so halving GFR doubles creatinine. The red point is the patient now: during injury it sits left of the curve and climbs toward it, in recovery it sits right of it and falls. The blue diamond is the GFR a steady-state reading of this creatinine implies, the assumption every eGFR equation makes.

Localisation

Where the injury is

Before the kidney, in it, or after it. The site of injury decides how the tubules handle sodium and water and what reaches the urine, which is why urine sodium, osmolality and the sediment help localise AKI.

cortex medulla afferent arteriole glomerulus proximal tubule loop of Henle distal tubule collecting duct ureter, bladder

Pre-renal

filtratered cellwhite cellcast

Indices hold best in oliguric AKI before diuretics or fluids. Calculate FeNa and FeUrea in the bedside section.

Bedside

Stage, localise, estimate

Three calculators in the order you would use them: KDIGO staging of AKI, fractional excretion to separate pre-renal from tubular injury, and CKD-EPI 2021 with the KDIGO risk grid for chronic disease. Each accepts a comma as the decimal mark.

KDIGO AKI staging

Illustrative values, not real patients.

mL/kg/h
hours

    FeNa and FeUrea

    Illustrative values, not real patients. Urine creatinine is usually reported in mmol/L and plasma creatinine in µmol/L, so each has its own unit.

    mmol/L
    mmol/L

      eGFR and CKD risk

      Illustrative values, not real patients. CKD-EPI 2021 does not use race.

      years

        GFR categoryA1<3 mg/mmolA23–30A3>30

        Cells show suggested monitoring visits per year. ACR in mg/g: A1 <30, A2 30–300, A3 >300. eGFR in mL/min/1.73 m².

        Reference

        Complications, dialysis and treatment

        What to look for as GFR falls, when to call for urgent dialysis, and the core of KDIGO 2024 management.

        CKD complications by stage

        ComplicationUsually fromCheckNote
        Renal anaemiaG3b, commoner in G4–G5Hb; ferritin and transferrin saturationReduced erythropoietin with iron deficiency or block. Correct iron first; erythropoiesis-stimulating agents under specialist care.
        CKD–mineral and bone disorderPTH from G3a; phosphate from G4Calcium, phosphate, PTH, ALP, 25-hydroxyvitamin DFalling calcitriol and phosphate retention drive secondary hyperparathyroidism. Raises vascular calcification and fracture risk.
        Metabolic acidosisG4–G5Venous bicarbonateReduced ammonium excretion. Normal anion gap at first, raised in advanced disease.
        HyperkalaemiaG4–G5; earlier with RAS blockade, MRA, diabetesK⁺ and creatinine 2–4 weeks after starting or increasing ACE inhibitor, ARB or finerenoneContinue the ACE inhibitor or ARB unless creatinine rises by more than 30% within 4 weeks.
        HypertensionAll stages, rising as GFR fallsStandardised office BPDriven by sodium and volume retention and RAS activation. SBP target below.
        Drug dosingG3a onward (eGFR <60)Every prescriptionAdjust renally cleared drugs (metformin, DOACs, gabapentinoids, low-molecular-weight heparin, aminoglycosides). Avoid NSAIDs. Where a label states dosing by clearance in mL/min, use the method it specifies.

        Indications for urgent dialysis

        IndicationDetail
        HyperkalaemiaRefractory to medical treatment, or rising despite it
        Metabolic acidosisSevere and refractory to medical treatment
        Fluid overloadRefractory to diuretics, particularly with pulmonary oedema
        Uraemic complicationsPericarditis, encephalopathy, uraemic bleeding
        Dialysable toxinsLithium, toxic alcohols (methanol, ethylene glycol), salicylate

        Key CKD management

        MeasureForNote
        ACE inhibitor or ARBAlbuminuria or hypertensionTitrate to the maximum tolerated dose. Check K⁺ and creatinine 2–4 weeks after each change.
        SGLT2 inhibitorCKD with eGFR ≥20With or without diabetes. Once started, it can be continued below 20 unless not tolerated or dialysis begins.
        FinerenoneType 2 diabetes with albuminuria on maximal tolerated RAS blockadeNeeds normal K⁺ and eGFR ≥25. Monitor K⁺.
        Blood pressureSBP <120 mmHg when toleratedKDIGO 2021, measured with standardised office technique.
        StatinAdults ≥50 with CKDStatin or statin with ezetimibe when not on dialysis.

        KDIGO 2024 CKD guideline, KDIGO 2021 blood pressure guideline and KDIGO 2012 AKI guideline.