Chronic kidney disease: eGFR and classification

Serum creatinine alone is an imperfect marker of renal function because it is affected by creatinine generation as well as filtration. eGFR provides a better estimate, but must be interpreted in clinical context.

Pathophysiology / principle

GFR reflects the kidney's overall filtering capacity
eGFR is calculated from serum creatinine with adjustment for factors that influence creatinine production
UK practice now uses CKD-EPI creatinine equations rather than MDRD
- the CKD-EPI formula is the recommended method for estimating GFR and calculating drug doses in most patients with renal impairment.
- CKD-EPI is adjusted for body surface area (BSA) and utilises serum creatinine, age, and sex as variables.
CKD is defined by abnormalities of kidney function or structure present for more than 3 months

Interpreting eGFR

eGFR is normalised to a body surface area of 1.73 m²
less reliable in:
- pregnancy
- extremes of muscle mass, e.g. amputees, body-builders, frailty
- acute kidney injury
- after eating cooked meat/red meat shortly before testing
eGFR may be mildly reduced with age; this alone does not diagnose CKD

CKD classification

classify CKD using both GFR category (G) and albuminuria category (A)
stages G1 and G2 require another marker of kidney disease, e.g. albuminuria, haematuria of renal origin, structural abnormality, or histological abnormality

G category	eGFR (mL/min/1.73 m²)
G1	90 or more
G2	60-89
G3a	45-59
G3b	30-44
G4	15-29
G5	less than 15

A category	ACR (mg/mmol)
A1	less than 3
A2	3-30
A3	more than 30

example: eGFR 95 with ACR 5 = CKD G1A2

+PassMedicine Notes

Pathophysiology / principle

GFR reflects the kidney's overall filtering capacity
eGFR is calculated from serum creatinine with adjustment for factors that influence creatinine production
UK practice now uses CKD-EPI creatinine equations rather than MDRD

the CKD-EPI formula is the recommended method for estimating GFR and calculating drug doses in most patients with renal impairment.
CKD-EPI is adjusted for body surface area (BSA) and utilises serum creatinine, age, and sex as variables.

CKD is defined by abnormalities of kidney function or structure present for more than 3 months

Interpreting eGFR

eGFR is normalised to a body surface area of 1.73 m2
less reliable in:

pregnancy
extremes of muscle mass, e.g. amputees, body-builders, frailty
acute kidney injury
after eating cooked meat/red meat shortly before testing

eGFR may be mildly reduced with age; this alone does not diagnose CKD

CKD classification

classify CKD using both GFR category (G) and albuminuria category (A)
stages G1 and G2 require another marker of kidney disease, e.g. albuminuria, haematuria of renal origin, structural abnormality, or histological abnormality

G category _ eGFR (mL/min/1.73 m2) | G1 _ 90 or more | G2 _ 60-89 | G3a _ 45-59 | G3b _ 30-44 | G4 _ 15-29 | G5 _ less than 15 | A category _ ACR (mg/mmol) | A1 _ less than 3 | A2 _ 3-30 | A3 _ more than 30 |