Normal GFR is 90+ mL/min/1.73m².

CKD stages: G1 (≥90): Normal with other kidney damage signs, G2 (60-89): Mild decrease, G3a (45-59): Mild-moderate decrease, G3b (30-44): Moderate-severe decrease, G4 (15-29): Severe decrease, G5 (<15): Kidney failure requiring dialysis.

Age-related decline is normal: 40s average 100, 70s average 70-75.

Concern if <60 for 3+ months or rapid decline.

CKD-EPI (2021) is now preferred by NKF/ASN for all patients.

It is more accurate than MDRD, especially for GFR >60.

Use CKD-EPI for: routine screening, GFR >60, medication dosing.

MDRD still acceptable for: diabetic nephropathy monitoring, GFR <60 where both formulas agree, historical comparisons.

The 2021 CKD-EPI update removed race coefficient, using only age, sex, and creatinine for equity.

Common causes: diabetes (leading cause 40%), hypertension (30%), glomerulonephritis, polycystic kidney disease, prolonged NSAID use, aging.

Seriousness by stage: G1-G2: Usually no symptoms, reversible if caught early.

G3a: Mild symptoms, manage with diet/medications.

G3b-G4: Fatigue, swelling, anemia - nephrology referral needed.

G5: Dialysis or transplant required.

Early detection critical - 90% of people with CKD do not know they have it.

Early-stage CKD (G1-G3a) can improve with treatment: control blood sugar (diabetes), manage blood pressure (<130/80), stop NSAIDs/nephrotoxic drugs, SGLT2 inhibitors (improve GFR 3-5 points), ACE inhibitors/ARBs (slow progression).

Lifestyle changes: low-sodium diet, adequate hydration, weight loss, smoking cessation.

Advanced CKD (G4-G5) rarely improves but progression can be slowed.

Monitor GFR every 3-6 months to track trends.

Muscle mass: High muscle (bodybuilders) falsely lowers GFR, low muscle (elderly, amputees) falsely raises GFR.

Diet: High-protein meal 24 hours before test can elevate creatinine.

Dehydration: Temporarily lowers GFR by 10-20%.

Medications: Trimethoprim, cimetidine block creatinine secretion.

Race: 2021 equation removed race adjustment.

Acute illness: Fever, infection distort results.

For accuracy: fast 8 hours, avoid exercise 24 hours, well-hydrated, repeat abnormal results.

Immediate referral: GFR <30 (G4-G5), rapidly declining GFR (>5 points/year), heavy proteinuria (>300 mg/day), difficult-to-control hypertension.

Routine referral: GFR 30-59 (G3b) with diabetes/hypertension, GFR <45 (G3b) without other causes, persistent hematuria with low GFR.

Primary care can manage: GFR 45-59 (G3a) stable, GFR >60 with isolated finding.

Test frequency: G3 every 6 months, G4 every 3 months, G5 monthly.