Diagnosis of proteinuria in primary care

• dipstick urinanalysis - highly specific in detecting glomerular proteinuria - albuminuria - in excess of 300 mg/d
• dipstick urinanalysis will not detect microalbuminuria in early diabetic nephropathy (30-300mg/d); also will not detect Bence Jones protein
• if proteinuria is detected then it must be determined whether
  • the proteinuria is persistent?
  • the amount of protein excretion
• a 24-hour urine collection is indicated may be indicated if there is persistent proteinuria, protein detected on at least two urine samples (see notes)
• urine microscopy - will help identify proteinuria, microscopic haematuria and proteinuria is suggestive of glomerular disease

Notes (2):

• no need to perform 24 h urine collections for the quantitation of proteinuria in primary care
• positive dipstick test (1+ or greater) should result in a urine sample (preferably early morning) being sent to the laboratory for confirmation by measurement of the total protein:creatinine ratio or albumin:creatinine ratio (depending on local practice). Simultaneously, a midstream sample should be sent for culture to exclude urinary tract infection (UTI)
• urine protein:creatinine ratios >45 mg/mmol or albumin:creatinine ratios of >30 mg/mmol should be considered as positive tests for proteinuria.
• positive tests for proteinuria should be followed by tests to exclude postural proteinuria, by analysis of an early morning urine sample, unless this has already been done
• if a patient has two or more positive tests for proteinuria, preferably spaced by 1 to 2 weeks, the s/he should be diagnosed as having persistent proteinuria

Reference:

1. Update 1998; 57 (4): 255-61.
2. The Renal Association (May 2006).UK CKD Guidelines