Creatinine level in the blood is a sensitive and specific marker of kidney function. Creatinine is released from the skeletal muscles and therefore its value in blood is higher in those who have larger muscle mass.

Creatinine is normally thrown out by the kidneys through urine. When kidneys are working abnormally low, creatinine level in the blood rises.

On repeated checks, when this rise remains sustained for at least three months, the person is said to have chronic kidney disease.

Normal values for men are 0.7 to 1.1 mg/dL and for women are 0.6 to 0.9 mg/dL. These values vary from laboratory to laboratory and the same sample tested in two different labs will often give significantly different values.

The other simple test is to do urine test to look for proteins. Normally, protein is not present in urine. If it is present, it indicates kidney disease.

Symptoms of kidney disease do not appear till 90 % of the kidney function is lost and therefore screening of individuals at risk (see below) is of utmost importance.

If the kidney sizes on sonography are small (i.e. < 9.0 cm), that almost confirms the diagnosis of CKD.

Glomerular Filtration Rate (GFR)

Glomerular Filtration Rate is a parameter of kidney functions. It is the amount of blood that is cleared of waste substances ( e.g. urea, creatinine) every minute by the kidneys. In an ideal setup, it can be calculated by a tedious test involving injection of a substance and collection of timed blood samples and urine samples.

GFR can be estimated in the clinic by simple formulae based on creatinine level, body weight, race and age. This value is called estimated GFR (eGFR).

Normal values vary with race and dietary habits. Western population have a normal GFR of 100 to 125 mL/min. In Indian population, where people are of much smaller stature, have lesser muscle mass and have predominantly vegetarian diet, the GFR is commonly less than 100 mL/min.

However, a value of less than 60 mL/min is abnormal irrespective of age, race and muscle mass.

Stages of Kidney Disease

Based on GFR, National Kidney Foundation has divided CKD into five stages.