Kidney evaluation includes the determination of the glomerular filtration rate, estimated on the basis of the serum creatinine level and the level of albuminuria, assessed on the basis of urinary albumin to creatinine ratio.
Functional kidney abnormalities are related to the decreased GFR, whereas structural abnormalities are inferred from markers of kidney damage, including increased albuminuria and abnormalities in the urine sediment and imaging.
Urine albumin/creatinine ratio is a widely used initial method to estimate daily protein excretion in urine.
The implementation of the 24-hour urine collection is the most accurate procedure in practice to figure out the urinary protein excretion.
The difference between urine albumin/creatinine ratio and 24-hour urine collection is that former requires a urine sample to be collected only once at any time.
Creatinine is normally released into the urine at a constant rate.
The ratio of protein to creatinine roughly estimates the actual value gained from the 24-hour urine protein test.
The normal urine albumin/creatinine ratio is not more than 200 mg/g.
Current guidelines for albuminuria evaluation recommend the determination of the albumin to creatinine ratio in a spot urine sample as the initial test, usually by an early morning sampling.
This result is confirmed by assessing the albumin excretion rate in a timed urine collection.
Either a decreased GFR of less than 60 mL per minute per 1.73 m² of body surface area or increased albuminuria with a albumin to creatinine ratio of greater than 30 per milligrams per gram with albumin measured in milligrams and creatinine in grams constitutes the clinical criterion for the definition of acute kidney disease and chronic kidney disease, whereas the only criterion for acute kidney injury is decreased GFR from baseline.
Age, gender and race can affect results.
Values in men 17-250 mg/ gm and in women 25-355 mg/gm.
Young patients, men and African-Americans have higher urine creatinine levels and may underestimate albumin excretion rate in these patients.