332.1 🎓 醫孞生版

332.1.0.1 📌 䞀頁重點

332.1.0.1.1 Renal Functions (Six Key)
332.1.0.1.1.1 1. Excretion of Metabolic Waste
  • Urea (protein metabolism)
  • Creatinine (muscle metabolism — proxy for GFR)
  • Uric acid (purines)
  • Drugs + toxins
332.1.0.1.1.2 2. Fluid + Electrolyte Balance
  • Na, K, Cl, Ca, PO4, Mg
  • Water balance (ADH, AQP2)
  • Osmolality regulation
332.1.0.1.1.3 3. Acid-Base Balance
  • HCO3 reabsorption (proximal tubule)
  • H+ secretion + NH4+ excretion (distal tubule)
  • pH regulation 7.35-7.45
332.1.0.1.1.4 4. Blood Pressure Regulation
  • RAAS axis (renin from JG cells)
  • Pressure natriuresis
  • Volume control
332.1.0.1.1.5 5. Endocrine Functions
  • Erythropoietin (EPO) → RBC production
  • Calcitriol (1,25-OH-vitamin D) → Ca/PO4 absorption
  • Renin → Ang II → aldosterone
332.1.0.1.1.6 6. Gluconeogenesis
  • ~ 20% in proximal tubule
332.1.0.1.2 Renal Anatomy + Physiology
332.1.0.1.2.1 Macroanatomy
  • Two kidneys, retroperitoneal
  • ~ 12 cm length
  • Cortex + medulla
  • Renal pelvis → ureter → bladder
332.1.0.1.2.2 Microanatomy — Nephron
  • ~ 1 million nephrons per kidney
  • Glomerulus (filtration) + tubules (reabsorption/secretion)

Glomerulus: - Capillary loop in Bowman’s capsule - Filtration barrier: 1. Fenestrated endothelium 2. Glomerular basement membrane (GBM) 3. Podocyte foot processes + slit diaphragm (nephrin, podocin) - Mesangial cells + matrix

Tubule Sections: - Proximal tubule (PCT, PST): bulk reabsorption (Na, water, glucose, AA, HCO3) - Loop of Henle: thin descending (water permeable), thin + thick ascending (NaCl reabsorption) - Distal convoluted tubule (DCT): NaCl reabsorption (thiazide site) - Collecting duct (CD): principal cells (Na/water/K — aldosterone) + intercalated cells (acid-base)

332.1.0.1.2.3 Glomerular Filtration

Glomerular Filtration Rate (GFR): - Normal: 90-120 mL/min/1.73m² - Function of: - Hydrostatic pressure - Oncotic pressure - Filtration coefficient (Kf) - Permeability + surface area

Filtration Fraction: - GFR / RBF - Normal ~ 20%

332.1.0.1.3 eGFR (Estimated Glomerular Filtration Rate)
332.1.0.1.3.1 Formulas

CKD-EPI 2021 (Race-Free) — Preferred: - Variables: serum creatinine + age + sex - Eliminates race coefficient (more equitable) - Adopted ASN/NKF 2021

Cystatin C-Based: - Useful when creatinine misleading (muscle wasting, athletes, elderly) - Less affected by muscle mass

Combined Cr + Cystatin C: - Most accurate - ASN recommends for refined estimation

Older Formulas (Historical): - MDRD (4-variable) — less accurate - Cockcroft-Gault — uses weight; OK for drug dosing

332.1.0.1.3.2 Limitations
  • Creatinine secretion by tubules (overestimates GFR)
  • Diet (high protein, creatine supplements)
  • Muscle mass variation
  • Race (now removed)
332.1.0.1.3.3 Measured GFR
  • Inulin clearance (gold standard, research)
  • Iothalamate
  • Cr-EDTA
  • DTPA scan
332.1.0.1.4 Urinalysis
332.1.0.1.4.1 Dipstick + Reflex Microscopy

Specific Gravity: 1.005-1.025 - Concentrated: dehydration - Dilute: DI, polydipsia

pH: 5.0-8.0 - Acid: high protein, DM, acidosis - Alkaline: vegetarian, UTI (urea-splitting), distal RTA

Glucose: positive - DM (uncontrolled) - SGLT2 inhibitor - Pregnancy - Fanconi syndrome

Ketones: positive - DKA - Starvation - Pregnancy

Blood: - RBC: glomerular, stones, UTI, tumor, trauma - Free Hb (hemolysis) - Myoglobin (rhabdomyolysis) - Distinguishing: dipstick + RBC absent → myoglobin/Hb

Protein: dipstick mainly albumin - > 30 mg/dL = albuminuria - UACR (urine albumin/creatinine ratio) more accurate - Microalbuminuria: 30-300 mg/g creatinine - Macroalbuminuria: > 300 mg/g - Nephrotic range: > 3.5 g/day or > 3500 mg/g

Leukocyte Esterase: UTI screening

Nitrites: UTI from nitrate-reducing bacteria

332.1.0.1.4.2 Sediment

RBCs: - > 5 per HPF abnormal - Dysmorphic = glomerular - Acanthocytes (ring with bleb)

WBCs: - > 5 per HPF abnormal - UTI, interstitial nephritis, glomerular

Casts: - Hyaline: normal in concentrated urine; not pathological - RBC cast: glomerular bleeding (GN) - WBC cast: pyelonephritis, interstitial nephritis - Granular cast: ATN, glomerular disease - Muddy brown cast: ATN (classic) - Waxy cast: chronic disease - Fatty cast: nephrotic syndrome

Crystals: - Calcium oxalate (stones, ethylene glycol) - Uric acid (gout, TLS) - Cystine (cystinuria) - Triple phosphate / struvite (UTI urease-splitting)

332.1.0.1.5 Proteinuria Assessment
332.1.0.1.5.1 UACR (Urine Albumin/Creatinine Ratio)
  • Spot urine sample
  • A1: < 30 mg/g (normal)
  • A2: 30-300 mg/g (moderately ↑, microalbuminuria)
  • A3: > 300 mg/g (severely ↑, macroalbuminuria)
332.1.0.1.5.2 24-hour Urine Protein

  • 3.5 g/24h = nephrotic range

  • More accurate quantification
  • Inconvenient
332.1.0.1.5.3 Spot Urine Protein/Creatinine Ratio (UPCR)
  • Less accurate than UACR (includes non-albumin proteins)
  • Useful for nephrotic-range monitoring
332.1.0.1.6 Major Patient Presentations

332.1.1 Acute Kidney Injury (AKI)

  • Rapid decline of kidney function
  • Cr ↑ > 0.3 mg/dL in 48 hr OR
  • Cr ↑ > 50% in 7 days OR
  • UO < 0.5 mL/kg/h × 6 hr
  • See Ch332

332.1.2 Chronic Kidney Disease (CKD)

  • eGFR < 60 OR
  • Kidney damage (albuminuria, hematuria, imaging) for ≥ 3 months
  • See Ch334

332.1.3 Nephrotic Syndrome

  • Proteinuria > 3.5 g/24h
  • Hypoalbuminemia
  • Edema
  • Hyperlipidemia
  • ± Hypercoagulability
  • See Ch338-339

332.1.4 Nephritic Syndrome

  • Hematuria + RBC casts
  • HTN
  • Edema
  • Variable proteinuria
  • ± AKI
  • See Ch338-339

332.1.5 Urinary Tract Infection (UTI)

  • Dysuria, frequency, urgency, hematuria
  • See Ch344

332.1.6 Nephrolithiasis (Kidney Stones)

  • Flank pain (renal colic)
  • Hematuria
  • See Ch343

332.1.7 Obstruction

  • Hydronephrosis on imaging
  • Often asymptomatic until late
332.1.7.0.1 Electrolyte Disorders Overview
332.1.7.0.1.1 Sodium (Na)
  • Hyponatremia (Na < 135): SIADH, cirrhosis, HF, hypothyroid, adrenal insufficiency, polydipsia
  • Hypernatremia (Na > 145): water loss > Na (DI, GI, sweat); rare polydipsia
332.1.7.0.1.2 Potassium (K)
  • Hypokalemia (K < 3.5): GI loss, renal loss (diuretics, hyperaldosterone), Mg deficiency, alkalosis
  • Hyperkalemia (K > 5): AKI, CKD, ACE/ARB/MRA, K-sparing diuretic, RTA-IV, pseudohyperkalemia
332.1.7.0.1.3 Calcium (Ca)
  • Hypercalcemia: hyperPTH, malignancy (PTHrP), vitamin D excess, thiazide, sarcoidosis
  • Hypocalcemia: hypoPTH, CKD, vitamin D deficiency, magnesium deficiency, hyperphosphatemia, pancreatitis
332.1.7.0.1.4 Phosphate (PO4)
  • Hyperphosphatemia: CKD, rhabdomyolysis, TLS, hypoPTH
  • Hypophosphatemia: refeeding, alkalosis, alcoholism, hyperPTH
332.1.7.0.1.5 Magnesium (Mg)
  • Hypomagnesemia: alcohol, GI loss, refeeding, PPI long-term, diuretics
  • Hypermagnesemia: CKD + Mg intake (laxative, antacid)
332.1.7.0.2 Acid-Base
332.1.7.0.2.1 Anion Gap
  • AG = Na - (Cl + HCO3)
  • Normal: 8-12
  • High AG metabolic acidosis (MUDPILES):
    • Methanol
    • Uremia
    • DKA
    • Paraldehyde
    • Iron, INH
    • Lactic acidosis
    • Ethylene glycol
    • Salicylates
  • Non-AG (hyperchloremic) acidosis: GI loss (diarrhea), RTA, NaCl IV
  • Metabolic alkalosis: vomiting, NG suction, diuretics, hyperaldo
332.1.7.0.2.2 Respiratory
  • Respiratory acidosis: ↑ PaCO2 (hypoventilation)
  • Respiratory alkalosis: ↓ PaCO2 (hyperventilation)

332.1.7.1 🩺 床邊速查

  • eGFR: CKD-EPI 2021 race-free (preferred); cystatin C for muscle issues
  • UACR: A1 < 30, A2 30-300, A3 > 300 mg/g
  • Glomerular: dysmorphic RBC, RBC casts, proteinuria
  • Tubular: muddy brown casts, AKI, electrolyte abnormalities
  • Interstitial: WBC casts, eosinophils, drug-induced
  • AKI vs CKD: time course + imaging
  • Anion gap MUDPILES: methanol, uremia, DKA, INH, lactic, ethylene glycol, salicylates