332.3 🏥 內科專科考前版

332.3.1 Mechanistic Deep Dive

332.3.1.1 Renal Blood Flow

  • ~ 20-25% of cardiac output
  • 1200 mL/min total
  • Filtration fraction ~ 20%
  • Autoregulation maintains stable GFR (myogenic + tubuloglomerular feedback)

332.3.1.2 Tubuloglomerular Feedback (TGF)

  • Macula densa senses Cl- delivery
  • Adenosine + others modulate afferent arteriole
  • Maintains GFR

332.3.1.3 RAAS in Detail

  • Renin (JG cells) → angiotensinogen → Ang I → ACE → Ang II
  • Ang II: vasoconstriction (efferent > afferent), aldosterone
  • Aldosterone: Na retention, K excretion, fibrosis
  • AT1R (vasoconstriction, growth) vs AT2R (vasodilation, anti-proliferation)

332.3.1.4 Acid-Base in Kidney

  • HCO3 reabsorption (PCT, 90%)
  • NH4 excretion (distal acidification)
  • Acid base disorders → urine pH, urine anion gap

332.3.1.5 Solute Handling

Sodium: - Filtered ~ 26,000 mEq/d - 65% PCT, 25% LoH, 5-10% DCT, <5% CD - Aldosterone in CD

Potassium: - Reabsorbed mostly PCT + LoH - Distal CD: secretion or reabsorption (depending on K state) - Aldosterone → K secretion

Calcium: - 70% PCT, 20% LoH, 5-10% DCT, 5% CD - PTH ↑ DCT reabsorption - Vitamin D ↑ absorption

332.3.2 Recent Trials & Updates

332.3.2.1 CKD-EPI 2021 Race-Free Equation

  • Adopted by ASN/NKF 2021
  • Removes race coefficient
  • More equitable
  • Combined Cr + cystatin C even better

332.3.2.2 SGLT2i in CKD (FLOW, DAPA-CKD, EMPA-KIDNEY)

  • Beyond DM
  • Dapagliflozin DAPA-CKD: CKD with or without DM
  • Empagliflozin EMPA-KIDNEY: similar
  • FLOW (2024): semaglutide for CKD

332.3.2.3 Finerenone in CKD (FIDELIO-DKD, FIGARO-DKD)

  • Non-steroidal selective MRA
  • Reduces CKD progression + CV events
  • FDA approved for DKD + albuminuria

332.3.2.4 APOL1 Studies

  • Inaxaplin (formerly VX-147): targeted for APOL1 nephropathy
  • Phase 3 trials ongoing

332.3.3 High-Yield Specialist Points

332.3.3.1 Drug Dosing in CKD

  • Use Cockcroft-Gault for many drugs (FDA historical)
  • eGFR (CKD-EPI) for newer labels
  • Some drugs require dose adjustment

332.3.3.2 Vitamin D in CKD

  • 25-OH vitamin D (storage form)
  • 1,25-OH vitamin D = calcitriol (active)
  • 1α-hydroxylase in kidney
  • Deficiency in CKD → 2° hyperparathyroidism → CKD-MBD

332.3.3.3 Anemia in CKD

  • Reduced EPO production
  • Iron deficiency
  • Erythropoiesis-stimulating agents (ESAs)
  • Iron supplementation
  • HIF-PHI (roxadustat, vadadustat, daprodustat) — newer

332.3.3.4 CKD-MBD (Mineral Bone Disorder)

  • Hyperphosphatemia
  • ↓ Vitamin D
  • ↑ PTH (secondary hyperparathyroidism)
  • ↑ FGF-23
  • Vascular calcification
  • Treatment: phosphate binders, calcitriol or analog, cinacalcet, etelcalcetide

332.3.3.5 Cardiovascular in CKD

  • CKD = CHD risk equivalent
  • HF, stroke, MI very common
  • Top cause of death in CKD

332.3.3.6 Glomerular Disease Workup

  • UACR, sediment
  • ANA, dsDNA, complement, ANCA, anti-GBM
  • Hepatitis serologies (HBV, HCV)
  • HIV
  • Free light chains
  • Cryoglobulins
  • Renal biopsy

332.3.3.7 Imaging

  • US: size, hydronephrosis
  • CT: stones, masses
  • MRI: vascular, masses
  • Nuclear: function, scar

332.3.4 Pearls

  • eGFR: CKD-EPI 2021 race-free preferred
  • UACR: A1 (< 30), A2 (30-300), A3 (> 300 mg/g)
  • Nephrotic: > 3.5 g protein + hypoalbuminemia + edema + hyperlipidemia
  • Nephritic: hematuria + RBC casts + HTN + AKI variable
  • Casts: muddy brown (ATN), RBC (GN), WBC (AIN/pyelo), waxy (chronic), fatty (nephrotic)
  • MUDPILES for anion gap acidosis
  • APOL1: African ancestry risk genotype for nephropathy
  • 2024 CKD therapies: SGLT2i + finerenone + GLP-1 RA (FLOW)