D'Arcy Little, MD, CCFP
Director of Medical Education,
York Community Services, Toronto, ON
Proteinuria, defined as the presence of urinary protein in concentrations greater than 0.3 g/d on a 24-hour collection, or greater than 1+ protein on a dipstick, is a common finding, which occurs in approximately 10% of elderly patients.1 Although proteinuria has been regarded as "the first sign of serious renal disease",2 its presence can represent anything from a benign abnormality to the signpost of significant disease,1 with the potential for progressive renal insufficiency.3 Because of the variable significance and multiple causes of proteinuria, the clinician requires a systematic approach for the work-up of this condition in the older patient. This paper will review the renal physiology associated with proteinuria, the classification of proteinuria, and an approach to the diagnosis of proteinuria in the older patient.
Approximately 15 kilograms of protein passes through the adult kidney in a single day.3 However, in a healthy adult, only up to 150 mg of protein should be excreted per day, for protein excretion levels to be considered normal.