eGFR guide: equation choice, indexed and absolute GFR

Which equation is suggested

The result at the top comes from the equation that fits the patient’s age and the markers entered. For adults this is EKFC, or EKFC Creatinine-Cystatin C when both markers are available. Under 18 it is CKiD U25, which needs height (without height, EKFC from age 2), and for babies born at term, up to 4 weeks old, the neonatal equation. EKFC is preferred over CKD-EPI because one equation covers everyone from age 2 without a jump at 18, and it was validated against measured GFR in European cohorts (Pottel et al., Ann Intern Med 2021). Equations outside their validated age range are never suggested, and neither is KRS, the kidney recipient specific equation developed in transplant recipients. Any other validated equation can be shown at the top from the list.

Indexed and absolute GFR

Most equations report GFR indexed to a body surface area of 1.73 m², in mL/min/1.73 m². This is the value used to classify CKD and to follow kidney function over time, and the KDIGO categories are defined on it.

Absolute GFR, in mL/min, is the indexed value multiplied by the patient’s body surface area and divided by 1.73. It is the relevant value for dosing drugs cleared by the kidneys, particularly in patients far from average size: KDIGO 2024 advises non-indexed eGFR for drug dosing at extremes of body weight. Formulas such as Calvert’s for carboplatin also expect mL/min. For a woman of 160 cm and 50 kg with an indexed eGFR of 60, absolute GFR is 52 mL/min; for a man of 190 cm and 110 kg with the same indexed value, it is 83 mL/min.

Cockcroft-Gault estimates creatinine clearance in mL/min rather than GFR, and many drug labels still base their dosing tables on it. Once height and weight are entered, the calculator shows both values for every equation except Cockcroft-Gault, which has only mL/min. Body surface area comes from the DuBois formula in adults and the Haycock formula under 18.

KDIGO GFR and albuminuria categories

CKD is defined as a GFR below 60 mL/min/1.73 m², or markers of kidney damage such as albuminuria, for more than 3 months (KDIGO 2024). The categories do not apply to children under 2.