Chronic kidney disease (CKD) is defined by evidence of kidney damage or reduced kidney function that persists for at least three months. An estimated glomerular filtration rate (eGFR/GFR) below 60 mL/min sustained over that timeframe is an objective indicator of chronically decreased renal function and supports CKD identification and staging in the outpatient record. This is why outpatient CDI programs frequently use trended eGFR as a clinical indicator to prompt documentation of CKD stage (e.g., stage 3a/3b, stage 4, etc.) when appropriate. BNP >1000 is more aligned with heart failure severity/volume status rather than kidney damage. BUN <12 is within/near normal and does not indicate renal impairment (elevated BUN may be seen with renal dysfunction but is less specific and affected by hydration, diet, GI bleed). Glucose >100 is a screening indicator for impaired fasting glucose/prediabetes but does not, by itself, establish chronic kidney damage. Therefore, sustained GFR <60 is the best objective lab-based measure of chronic kidney damage over time.