Proteinuria is protein in the urine.
Proteinuria is defined as:
- albumin:creatinine ratio >30mg/mmol or albumin concentration >200mg/l
- urine protein:creatinine ratios >45 mg/mmol (2)
The loss of up to 150 mg of protein per day is normal; this may be expressed as normal is less than 4 mg per hour per square metre of body surface area.
Proteinuria may be increased by a factor of 2-3 times by strenuous exercise or fever.
- other causes of transient include urinary tract infection, vaginal mucus, orthostatic proteinuria (occurs after patient has been upright for some time and is not found in early morning urine - this condition is uncommon in patients over 30 years old) and pregnancy
Causes of persistent proteinuria include:
- primary renal disease: this may be glomerular (e.g. glomerulonephritis) or tubular
- secondary renal disease: diabetes mellitus, hypertension, connective tissue diseases, vasculitis, amyloidosis, myeloma, congestive cardiac failure
- NICE suggest that (2):
- all people with diabetes, and people without diabetes with a GFR less than 60 ml/min/1.73 m^2, should have their urinary albumin/protein excretion quantified. The first abnormal result should be confirmed on an early morning sample (if not previously obtained)
- quantify by laboratory testing the urinary albumin/protein excretion of people with an eGFR 60 ml/min/1.73 m2 or more if there is a strong suspicion of CKD
- for the initial detection of proteinuria, if the albumin:creatinine
ratio (ACR) is 30 mg/mmol or more (this is approximately equivalent to
protein: creatinine ratio (PCR) 50 mg/mmol or more, or a urinary protein
excretion 0.5 g/24 h or more) and less than 70 mg/mmol (approximately
equivalent to PCR less than 100 mg/mmol, or urinary protein excretion
less than 1 g/24 h) this should be confirmed by a subsequent early morning
- if the initial ACR is 70 mg/mmol or more, or the PCR 100 mg/mmol or more, a repeat sample need not be tested
- in people without diabetes consider clinically significant proteinuria to be present when the ACR is 30 mg/mmol or more (this is approximately equivalent to PCR 50 mg/mmol or more, or a urinary protein excretion 0.5 g/24 h or more)
- in people with diabetes consider microalbuminuria (ACR more than 2.5 mg/mmol in men and ACR more than 3.5 mg/mmol in women) to be clinically significant
- do not use reagent strips to identify proteinuria unless they are capable of specifically measuring albumin at low concentrations and expressing the result as an ACR
- to detect and identify proteinuria, use urine ACR in preference, as it has greater sensitivity than PCR for low levels of proteinuria. For quantification and monitoring of proteinuria, PCR can be used as an alternative. ACR is the recommended method for people with diabetes
- regard a confirmed ACR of 3 mg/mmol or more as clinically important proteinuria
- classification of ACR
ACR (albumin creatinine ratio) category ACR (mg/mmol) A1 <3 A2 3-30* A3 >30**
* Relative to young adult level
** Including nephrotic syndrome (ACR usually >220 mg/mmol)
- (1) MeReC Briefing 2004;26:1-8.
- (2) NICE (July 2014). Chronic Kidney Disease - Early identification and management of chronic kidney disease in adults in primary and secondary care
- (3) The Renal Association (May 2006).UK CKD Guidelines
- (4) Haynes J, Haynes R. Proteinuria. BMJ 2006;332:284.
Last reviewed 01/2018