eGFR 90 or higher mL/min/1.73m²

An eGFR of 90 or higher is what KDIGO calls "Normal or high," and on its own it is not kidney disease. The guideline's Table 2 footnote is explicit: "In the absence of evidence of kidney damage, neither G1 nor G2 fulfills the criteria for CKD." Chronic kidney disease needs one of two things for at least 3 months: a GFR under 60, or a marker of damage, and the marker KDIGO lists first is albumin in the urine at an albumin-to-creatinine ratio of 30 mg/g or higher. So the number that decides whether G1 means anything is not the eGFR. It is the urine ACR, and KDIGO says this "nuance is often missed by healthcare providers and students."

What KDIGO says to do. If your ACR is under 30 (category A1), the guideline's monitoring figure labels the cell "Screen" once a year, and its risk key reads "Low risk (if no other markers of kidney disease, no CKD)." If albumin is present, G1 is CKD and the figure switches to "Treat": once a year at A2 (ACR 30 to 300), three times a year at A3 (over 300). An incidental abnormal ACR is confirmed on a first-morning sample before anything is diagnosed, and KDIGO warns not to "assume chronicity based upon a single abnormal level for eGFR and ACR."

Treatment that applies at G1 with albuminuria. KDIGO recommends an ACE inhibitor or ARB for people with CKD and severely increased albuminuria without diabetes (Recommendation 3.6.1, grade 1B), suggests one at moderately increased albuminuria (3.6.2, 2C), and recommends one for either level with diabetes (3.6.3, 1B), in each case whether or not blood pressure is high. An SGLT2 inhibitor is recommended for anyone with type 2 diabetes and CKD (3.7.1, 1A) and for an ACR of 200 mg/g or higher, or heart failure, at any eGFR of 20 or above (3.7.2, 1A). For adults 50 and older with CKD at G1 or G2, a statin is recommended (3.15.1.2, 1B). None of those switch on for a G1 reading with a normal ACR.

A high number is not a better number. KDIGO notes that creatinine-based eGFR "exhibited a J-shaped association such that risk increased with eGFR values >105 ml/min per 1.73 m2," and attributes that to creatinine, not to true filtration: a low creatinine from low muscle mass reads as a high eGFR. The guideline's Table 8 lists the situations where creatinine misleads and cystatin C is the better basis, including eating disorders, amputation, spinal cord injury, cirrhosis, heart failure, cancer and class III obesity. And the kidney failure risk equations KDIGO recommends at G3 to G5 "may not be valid for use in those with CKD G1–G2," so no one should quote you a five-year risk from this band.