Albumin/Creatinine Ratio and Kidney Disease Progression

Classification and Clinical Significance

The Kidney Disease Improving Global Outcomes (KDIGO) guidelines categorize albuminuria as A1 (Normal to Mildly Increased): ACR <30 mg/g, A2 (Moderately Increased): ACR 30-299 mg/g, and A3 (Severely Increased): ACR ≥300 mg/g 1, 2
An albumin/creatinine ratio (ACR) of 455 mg/g indicates severely increased albuminuria (category A3), representing significant kidney damage and high risk for chronic kidney disease progression, cardiovascular events, and mortality 1, 2
The American College of Physicians and other guideline societies imply that an ACR of 455 mg/g is associated with increased risk of progression to end-stage renal disease, higher cardiovascular morbidity and mortality, and greater all-cause mortality 3, 4

The Kidney Disease Improving Global Outcomes (KDIGO) guidelines recommend confirming elevated ACR with repeat testing, with at least 2 of 3 specimens collected within a 3-6 month period showing abnormal results to establish persistent albuminuria 5, 4
Evaluation of estimated glomerular filtration rate (eGFR) is necessary to fully stage chronic kidney disease, according to the National Kidney Foundation and other guideline societies 3, 6

The American Diabetes Association and other guideline societies recommend implementing blood pressure control, targeting appropriate goals based on comorbidities, and optimizing glycemic control for patients with diabetes 3, 4
The use of renin-angiotensin system blockers (ACE inhibitors or ARBs) is recommended to reduce albuminuria and slow CKD progression, as suggested by the American Heart Association and other guideline societies 6, 7
Aiming for >30% sustained reduction in albuminuria is a treatment goal, according to the Kidney Disease Improving Global Outcomes (KDIGO) guidelines 5

Single ACR measurements can have up to 40-50% variability, and confirmation with repeat testing is essential, as noted by the National Institute of Diabetes and Digestive and Kidney Diseases and other guideline societies 5
False elevations in ACR can occur with hematuria, febrile illness, or vigorous exercise within 24 hours of collection, according to the American College of Physicians and other guideline societies 8
Morning spot urine samples are preferred for ACR measurement to minimize variability, as recommended by the Kidney Disease Improving Global Outcomes (KDIGO) guidelines 4

The KDIGO guideline categorizes albumin‑creatinine ratio (ACR) as A1 < 30 mg/g (normal to mildly increased), A2 30–299 mg/g (moderately increased, formerly “microalbuminuria”), and A3 ≥ 300 mg/g (severely increased). 13
KDIGO recommends abandoning the term “microalbuminuria” and using “moderately increased albuminuria” for ACR 30–299 mg/g and “severely increased albuminuria” for ACR ≥ 300 mg/g. 13

KDIGO advises that a first‑morning void urine specimen should be used for confirmatory ACR testing to reduce biological variability and to exclude orthostatic proteinuria, especially in children and young adults. [13][14]
KDIGO requires that any ACR ≥ 30 mg/g detected on a random, untimed urine sample be confirmed with a subsequent early‑morning urine specimen. 13
KDIGO notes that vigorous exercise within 24 hours can cause transient protein elevation and should be avoided before urine collection. 13

The American Society of Nephrology (ASN) states that urine ACR measured on a first‑morning midstream sample is the preferred initial test for albuminuria screening. 14
KDIGO mandates that clinical laboratories report ACR as a ratio (mg albumin per g creatinine) in addition to the absolute albumin concentration; reporting albumin concentration alone is insufficient. 13
ASN permits the use of reagent‑strip urinalysis for albumin with automated reading when quantitative ACR is unavailable, provided that positive results are confirmed with a quantitative ACR measurement. 14

KDIGO recommends assessing estimated glomerular filtration rate (eGFR) and albuminuria at least annually in individuals with chronic kidney disease. 13
KDIGO advises more intensive monitoring (every 3–6 months) for higher‑risk patients—those with eGFR 30–60 mL/min/1.73 m² or albuminuria > 300 mg/g. 13

ASN indicates that point‑of‑care ACR devices may be employed when laboratory access is limited, but they must participate in external quality assessment programs and follow the same pre‑analytical criteria as standard laboratory testing. 14