Proteinuria
Proteinuria is one of the most common signs of renal disease. Detection is now primarily by Stix testing. Most reagent strips can detect a concentration of 100 mg/L or more in urine. They react primarily with albumin and are relatively insensitive to globulin and Bence Jones proteins.
If proteinuria is confirmed on repeated Stix testing, protein excretion in 24-hour urine collections should be measured (but see below). Normal values for urinary protein excretion are dependent on the laboratory methods used and in particular whether or not the method measures Tamm-Horsfall glycoprotein, which is a normal constituent of urine. Results must therefore take account of the laboratory's normal reference range.
Given this caveat, healthy adults excrete approximately 60-100 mg of protein daily but up to 150-200 mg daily is within the acceptable range. Slightly higher values - up to 300 mg daily - may be excreted by adolescents.
Pyrexia, exercise and adoption of the upright posture all increase urinary protein output. Proteinuria, while occasionally benign, always requires further investigation.
Postural proteinuria
This term is used to refer to proteinuria present on dipstick testing which becomes undetectable after a period of hours lying flat. Typically, a negative dipstick result is obtained on the first urine passed on rising in the morning, whereas subsequent specimens give a positive result. This is regarded by many - including some insurance companies - as a benign condition.
Renal biopsy sometimes discloses glomerular abnormalities but progressive renal failure is rare.
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