GFR & ACR

In medical parlance, Kidney damage is defined by any one of the following findings:

1. Pathologic kidney abnormalities
2. Persistent proteinuria
3. Markers of kidney damage: albuminuria (ACR > 3 mg/mmol), haematuria (or presumed or confirmed renal origin), electrolyte abnormalities due to tubular disorders, renal histological abnormalities, structural abnormalities detected by imaging (e.g. polycystic kidneys, reflux nephropathy) or a history of kidney transplantation
4. Imaging abnormalities
5. eGFR<60mL/min/1.73m² separated by 90 days gap with or without markers of kidney damage.

A patient is said to have chronic kidney disease (CKD) if they have abnormalities of kidney function or structure present for more than 3 months. The definition of CKD includes all individuals with markers of kidney damage (point no c above) or those with an eGFR of less than 60 ml/min/1.73m2 on at least 2 occasions 90 days apart (with or without markers of kidney damage). GFR level has a lot to do with the age and eating habit of the patient.

Patients with CKD can be classified depending on their level of kidney function, or eGFR, and the amount of protein present in the urine (ACR).  The higher the stage (G1->G5) and the greater the amount of protein present in the urine (A1->A3) the more “severe” the CKD.

Glomerular Filtration Rate (GFR) measures the stages of kidney failure. Glomeruli are the tiny filters in the kidneys that filter waste from the blood. Glomerular Filtration Rate (GFR) is a test which estimates how much blood passes through the glomeruli each minute. GFR indicates the stage of Chronic Kidney Disease (CKD) of a patient. The lower the eGFR, higher the damage suffered by kidney. Stages of Chronic Kidney Disease based on e GFR is given in the table below:

*Because of greater cardiovascular disease risk and risk of disease progression at lower eGFRs, CKD Stage 3, is sub-divided into Stages 3A (45–59 mL/min/1.73 m2) and 3B (30–44 mL/min/1.73 m2)
CKD Stage 5 includes patients that may require or are undergoing kidney replacement therapy. Designations 5D and 5T indicate end-stage renal disease patients who undergo chronic dialysis (5D) treatment or have undergone kidney transplantation (5T).

Note: Glomerular filtration rate (GFR) is the total amount of plasma that is ultrafiltered across all the glomeruli of both the kidneys in unit time. Estimated glomerular filtration rate (eGFR) is a calculated estimate of the glomerular filtration rate and is therefore also referred to as the calculated GFR.

Albumin Creatinine Ratio (ACR): Albumin-to-creatinine ratio (ACR) is used to detect elevated protein in urine. When kidney functioning decreases, protein is leaked in urine. The level of protein in urine indicates the degree of kidney failure. ACR for determining categories of Chronic Kidney disease (CKD) is as follows:

• A1-<30mg/g (or <3mg/mmol): Normal to mildly increased risk of CKD
• A2->=30mg/g to 299mg/g (3-29 mg/mmol): Moderately increased risk of CKD
• A3->=300mg/g (or >=30 mg/mmol): Severe risk of CKD

Both GFR and ACR are taken together along with other parameters to estimate the stage of kidney disease. Screening for metabolic complications of CKD is typically not recommended in persons with eGFR >60 mL/min/1.73 m2 and no albuminuria, unless a genetic disorder with a high degree of penetrance is present (autosomal dominant polycystic kidney disease).