About Chronic Kidney Disease

Definition

Chronic Kidney Disease (CKD) is defined by:

eGFR < 60 mL/min/1.73m2 that is present for ≥ 3 months
- or -
Markers of kidney damage present for ≥ 3 months:

  • Albuminuria ≥ 3 mg/mmol
  • Urine sediment abnormalities
  • Structural or pathological abnormalities

If eGFR is ≥ 60 mL/min/1.73m2 , and there are no markers of kidney damage, then CKD is not present

 

Classification

CKD is classified based on eGFR and albuminuria categories.


eGFR Categories:

CategoryeGFR(mL/min/1.73 m2)Description
G1 >90 Normal or high
G2 60-89 Mildly decreased
G3a 45–59 Mildly to moderately decreased (CKD)
G3b 30–44 Moderately to severely decreased (CKD)
G4 15–29 Severely decreased (CKD)
G5 <15 Kidney failure (CKD)

Albuminuria (ACR) Categories:

CategoryACR(mg/mmol)Description
A1 <3 mg/mmol Normal to mildly increased
A2 3-30 mg/mmol Moderately increased (CKD)
A3 >30 mg/mmol Severely increased (CKD)
 

General
information about random urine ACR

Random urine ACR:

  • Excess amounts of protein in urine are a marker of kidney damage and increase kidney disease and CVD risk.
  • Random urine ACR is preferred to detect proteinuria (ideally first morning void).
  • ACR has greater sensitivity than protein:creatinine ratio (PCR) for low levels of proteinuria.
  • ACR ≥3.0 mg/mmol for both men and women is clinically significant.

Approximate equivalent values of ACR, PCR and urinary protein excretion:

ACR (mg/mmol)PCR (mg/mmol)Urinary protein excretion (g/24h)
30 50 0.5
60 100 1

Factors affecting urinary ACR:

FactorExamples of effect
Transient elevation in albuminuria
  • Menstrual blood contamination
  • Symptomatic UTI
  • Exercise
  • Upright posture (orthostatic proteinuria)
  • Other conditions increasing vascular permeability (e.g. septicemia)
Intraindividual variability
  • Intrinsic biological variability
  • Genetic variability
Pre-analytical storage conditions
  • Degradation of albumin before analysis
Non-renal causes of variability in creatinine excretion
  • Age (lower in children and older people)
  • Race (lower in Caucasian than black people)
  • Muscle mass (e.g. lower in people with amputations, paraplegia, muscular dystrophy)
  • Gender (lower in women)
Changes in creatinine excretion
  • Non-steady state for creatinine (AKI)
 

Prognosis and recommended frequency of testing per year

Early identification and management of CKD can reduce progression and cardiovascular risk. CKD prognosis for mortality, CVD and kidney function progression is determined by eGFR and albuminuria (ACR).

Albuminuria (ACR) Categories
A1 A2 A3
<3 mg/mmol 3-30 mg/mmol >30 mg/mmol

eGFR Categories

G1 ≥90
G2 60-89
G3a 45-59
G3b 30-44
G4 15-29
G5 <15