proteinuria

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Proteinuria is protein in the urine.

Proteinuria is defined as:

albumin:creatinine ratio >30mg/mmol or albumin concentration >200mg/l (1,2) or
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

Notes:

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 sample
- 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)

Reference:

Last reviewed 08/2018

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