Chronic kidney disease Study Guide

📖 Core Concepts Chronic Kidney Disease (CKD) – long‑lasting (≥ 3 months) loss of kidney function or structure. Estimated Glomerular Filtration Rate (eGFR) – the main numeric measure of kidney filtering ability; reported as mL/min/1.73 m². Albuminuria – excess albumin in urine; expressed as an albumin‑to‑creatinine ratio (ACR) ≥ 30 mg/g, indicating kidney damage even when eGFR is still normal. Stages 1‑5 – classification by eGFR (and albuminuria for early stages) that guides monitoring and treatment intensity. Key complications – hypertension, cardiovascular disease, electrolyte disturbances (hyper‑K⁺, hyper‑P), anemia, bone‑mineral disorders, metabolic acidosis, and eventual end‑stage renal disease (ESRD) requiring dialysis or transplant. 📌 Must Remember Diagnostic cut‑offs: eGFR < 60 mL/min/1.73 m² or ACR ≥ 30 mg/g → CKD. Staging: Stage 1: eGFR ≥ 90 + albuminuria Stage 2: eGFR 60‑89 + damage Stage 3A: eGFR 45‑59 Stage 3B: eGFR 30‑44 Stage 4: eGFR 15‑29 (prep for RRT) Stage 5: eGFR < 15 (ESRD) Hyperkalemia threshold: eGFR < 20‑25 mL/min/1.73 m² → risk of dangerous K⁺ elevation. First‑line BP meds: ACE inhibitors or ARBs (slow GFR decline & lower CV events). Statin indication: age > 50 yr or younger with extra risk factors. Anemia target: hemoglobin 100‑120 g/L; >120 g/L offers no extra benefit. Referral triggers: eGFR < 30, decline > 3 mL/min/1.73 m² / yr, or ACR > 30 mg/mmol. 🔄 Key Processes Screening workflow Identify high‑risk individuals (DM, HTN, >60 yr, African ancestry, family history). Draw serum creatinine → calculate eGFR. Collect first‑morning urine → measure ACR. CKD staging determination If eGFR ≥ 60, look for persistent albuminuria → Stage 1/2. If eGFR < 60, assign stage based on the numeric range. Blood‑pressure management Start ACE‑I/ARB → titrate to target BP (usually <130/80 mmHg). Add thiazide or loop diuretic if needed for volume control. Anemia treatment algorithm Check Hb → if <100 g/L, give parenteral iron first. If iron replete and Hb still low, start erythropoietin‑stimulating agent (ESA). Bone‑mineral disorder control Monitor Ca, P, PTH, FGF‑23. Give calcitriol for vitamin D deficiency. Add phosphate binders when serum phosphate rises. 🔍 Key Comparisons ACE‑I vs ARB – both block the renin‑angiotensin system; ACE‑I also raise bradykinin (cough risk), ARB less likely to cause cough. Hyperkalemia vs Hyperphosphatemia – K⁺ rises when eGFR < 20‑25; phosphate rises earlier as filtration of P declines. Stage 3A vs 3B – 3A (45‑59) has slower progression and fewer symptoms than 3B (30‑44). Dialysis vs Transplant – dialysis prolongs survival vs conservative care; transplant offers better long‑term survival but higher early peri‑operative risk. ⚠️ Common Misunderstandings “Normal creatinine = normal kidney” – creatinine can be normal until eGFR falls ≈ 30 mL/min/1.73 m²; rely on eGFR and albuminuria. “All CKD patients need low‑protein diet” – protein restriction is most beneficial in advanced stages or high proteinuria; overly low protein can cause malnutrition. “Statins are useless in CKD” – they reduce cardiovascular events in patients > 50 yr and are recommended despite reduced renal clearance. “Dialysis cures CKD” – dialysis replaces filtration but does not halt underlying disease; transplant is the only definitive cure. 🧠 Mental Models / Intuition “Filter‑Leak‑Fire” – As GFR (filter) drops, wastes and electrolytes “leak” (hyper‑K, hyper‑P) and “fire” (metabolic acidosis, bone disease). Remember the cascade: ↓GFR → ↑toxins → CV stress → mortality. “Staging ladder” – Visualize CKD as a ladder: each step down (lower eGFR) adds a new set of complications and triggers tighter interventions. 🚩 Exceptions & Edge Cases Gadolinium contrast – contraindicated only when eGFR < 30 mL/min/1.73 m² (risk of nephrogenic systemic fibrosis). Sodium restriction – very aggressive restriction can cause hypotension, especially in patients on ACE‑I/ARB. Lithium‑induced CKD – occurs in 1‑5 % after 10‑20 yr; stop lithium if CKD progresses. 📍 When to Use Which Choose ACE‑I vs ARB – start ACE‑I; switch to ARB if cough or angioedema develop. Phosphate binder vs dietary phosphate restriction – use binders when serum P > 5.5 mg/dL despite low‑phosphate diet. ESA vs iron alone – give iron first; add ESA only after iron repletion if anemia persists. Dialysis modality – consider home high‑intensity hemodialysis for better survival/quality of life; peritoneal dialysis if vascular access is problematic. 👀 Patterns to Recognize eGFR < 30 + rapid decline → imminent need for nephrology referral and RRT planning. Hyperkalemia + metabolic acidosis – both appear when eGFR falls below 25 mL/min/1.73 m². Persistent albuminuria with normal eGFR – early CKD (Stage 1) – treat aggressively to prevent GFR loss. Elevated FGF‑23 + low 1,25‑vit D – classic for secondary hyperparathyroidism in CKD. 🗂️ Exam Traps “CKD is diagnosed only when eGFR < 60” – false; persistent albuminuria also meets criteria. “All CKD patients need dialysis at eGFR = 15” – false; decision depends on symptoms, volume status, and patient preferences. “ACE‑I are contraindicated in CKD” – false; they are first‑line unless hyperkalemia or AKI develops. “Statins are harmful in CKD because of liver metabolism” – misleading; benefits outweigh risks, especially > 50 yr. “Hyperphosphatemia only occurs in Stage 5” – false; phosphate rises as early as Stage 3 due to reduced excretion.