Chronic Kidney Disease Assessment

Definition and Classification

Normal GFR in adults ranges from 90-120 mL/min/1.73 m² for those under 40 years of age, with values progressively declining after age 40, and values between 60-89 mL/min/1.73 m² considered mildly decreased 1
The American College of Physicians recommends that GFR ≥90 mL/min/1.73 m² is generally considered normal kidney function, though CKD diagnosis requires additional markers of kidney damage (e.g., albuminuria) 1
The CKD-EPI equation is recommended for reporting eGFR in adults as it has less bias than the MDRD equation, especially at GFR ≥60 mL/min/1.73 m² 1
The CKD-EPI equation for estimating eGFR is: eGFR (mL/min/1.73 m²) = 186 × [SCr (mg/dL)]^-1.154 × [age (years)]^-0.203 × [0.742 if female] × [1.21 if African American], although a race-free version updated in 2021 is now preferred 2, 3
For children and adolescents (>2 years), a normal eGFR is typically considered to be ≥90 mL/min/1.73 m², with values <90 mL/min/1.73 m² flagged as "low" in this age group 4

The National Kidney Foundation Kidney Disease Outcomes Quality Initiative (K/DOQI) classification system defines CKD stages based on GFR as follows:

Stage	Description	GFR (mL/min/1.73 m²)
1	Kidney damage with normal or increased GFR	≥90
2	Kidney damage with mild decrease in GFR	60-89
3a	Mild to moderate decrease in GFR	45-59
3b	Moderate to severe decrease in GFR	30-44
4	Severe decrease in GFR	15-29
5	Kidney failure	<15 or dialysis	[2, 5, 6, 3, 7]

GFR should be interpreted alongside albuminuria for comprehensive kidney function assessment 8, 9
The National Kidney Foundation recommends the following risk categories: Low risk (GFR ≥60 mL/min/1.73 m² with normal/mildly increased albuminuria), Moderate risk (GFR ≥60 mL/min/1.73 m² with moderately increased albuminuria OR GFR 45-59 mL/min/1.73 m² with normal/mildly increased albuminuria), High risk (various combinations of decreased GFR and increased albuminuria), and Very high risk (severely decreased GFR (<30 mL/min/1.73 m²) with any degree of albuminuria) 8
The British Medical Association recommends that the frequency of GFR monitoring should be based on the risk category: Low risk (Annual monitoring), Moderate risk (1-2 times per year), High risk (2-3 times per year), and Very high risk (3-4 times per year) 8, 9
The American Journal of Kidney Diseases recommends using age-appropriate equations, such as the CKD-EPI equation for adults, to estimate glomerular filtration rate (GFR), with specific considerations for elderly patients where BIS1 or FAS equations may be more appropriate 4
Serum creatinine alone is inadequate for GFR estimation, particularly in elderly patients, those with reduced muscle mass, or malnutrition 2
Special populations, such as obese individuals and transgender individuals, require consideration when estimating eGFR, as certain equations may be less reliable 4, 2

Stage 2 CKD diagnosis requires evidence of kidney damage (such as albuminuria) in addition to the GFR value, according to KDOQI guidelines 3
Patients with a GFR of 17 mL/min/1.73 m² should be referred to nephrology care immediately, as this GFR level represents severe kidney disease 10
Referral to a nephrologist should be considered for patients with eGFR <45 mL/min/1.73m², as this is associated with a 3.5-fold increased risk of death compared to stages 1-2, and increased risk of diabetes, heart failure, and hypertension, according to clinical guidelines 11

Hypertension is a risk factor for progressive kidney damage, and careful blood pressure management is necessary to preserve kidney function, according to the European Society of Cardiology and the American Heart Association 12, 13
Target blood pressure should be <130/80 mmHg, with first-line agents being ACE inhibitors or ARBs, particularly if albuminuria is present, according to the KDOQI guidelines and the American College of Cardiology 3
Statin therapy for lipid management and aspirin for secondary prevention in those with established cardiovascular disease are also recommended, according to the KDOQI guidelines 3
Lifestyle modifications, including regular physical activity, weight management, smoking cessation, and alcohol moderation, are recommended, according to the KDOQI guidelines 3
Sodium restriction (<2.3 g/day), moderate protein intake (0.8 g/kg/day), potassium restriction if hyperkalemic, and phosphorus restriction if hyperphosphatemic, are recommended, according to the KDOQI guidelines 3

Monitoring for complications of advanced kidney disease, such as electrolyte abnormalities, metabolic acidosis, anemia, mineral bone disorder, and uremic symptoms, is crucial, according to the American Journal of Kidney Diseases guidelines 14
Preparation for kidney failure treatment options should be initiated, including education about kidney transplantation, peritoneal dialysis, hemodialysis, and conservative management, as suggested by the American Journal of Kidney Diseases guidelines 15
The decision to initiate dialysis should be based on the presence of uremic symptoms, volume status and blood pressure control difficulties, nutritional status, overall clinical condition, and patient preference after informed discussion, with most patients beginning dialysis when their GFR falls below 15 mL/min/1.73 m² (stage 5) 3, 7
The Kidney Failure Risk Equation (KFRE) can provide more precise risk stratification by incorporating age, sex, eGFR, and albuminuria, to assess the risk of progression to ESRD requiring dialysis or transplantation within 5 years 3, 7
Discontinuing potentially nephrotoxic medications and adjusting dosages of medications cleared by kidneys is essential to preserve remaining kidney function, as implied by the need for urgent evaluation and intervention 5