Response from bpacnz editorial team:
Proteinuria is a sign of chronic kidney disease (CKD) as well as being an indicator for progressive CKD and future cardiovascular
events.1 Many clinicians will routinely use urine dipstick to test for proteinuria. However, New Zealand guidelines
now recommend assessing patients with risk factors for CKD with urinary albumin:creatinine ratio (ACR), serum creatinine
and blood pressure testing;2 the addition of these tests to all diabetes screening and cardiovascular risk
assessments is also recommended.3 The frequency of CKD testing for patients with risk factors is:2
- At least every one to two years for patients without CKD
- At least every 12 months for patients with diabetes
ACR is the preferred method for quantifying proteinuria because:1
- Urinary dipstick is not sensitive enough to reliably detect proteinuria (see below)
- Albumin is the main protein excreted in the vast majority of proteinuric kidney disease
- ACR provides greater sensitivity in the detection of lower, but clinically significant, proteinuria compared with
measures of total protein, i.e. protein:creatinine ratio (PCR)
Despite it being a rapid and simple point-of-care test the ability of urine dipstick to detect anything other than overt
proteinuria is limited.4 In a sample of urinalysis results for more than 10,000 Australian adults aged 25 years
and older, a dipstick test result ≥ 1+ protein identified ACR ≥ 3.4 mg/mmol, i.e. microalbuminuria, with 57.8% sensitivity
and 95.4% specificity, meaning four out of ten patients with microalbuminuria would be expected to return a false-negative
result on urine dipstick testing.5 When the threshold for detection was raised to ACR ≥ 33.9 mg/mmol, i.e.
macroalbuminuria, the sensitivity of dipstick was increased to 98.9% with a specificity of 92.6%.5
The concern in using a negative result on urine dipstick to effectively “rule-out” clinically significant proteinuria
in patients with reduced renal function is that while patients with macroalbuminuria, who are admittedly at the highest
risk, are likely to be identified, some patients with microalbuminuria may be missed.
Urine dipstick can, however, provide useful information in some situations in patients with reduced renal function.
For example, dipstick testing for haematuria can provide useful diagnostic information.
It is acknowledged that routine ACR testing in all patients with a mildly reduced eGFR, i.e. 60–89 mL/min/1.73m2,
will include a substantial number of patients and an associated cost. It is important to remember
that in New Zealand 7–10% of the adult population is estimated to have CKD;3 with future rates of CKD expected
to rise secondary to the increasing prevalence of obesity and diabetes, early detection in primary care is a priority.
The overarching aim of CKD surveillance is to reduce the number of people reaching end-stage kidney disease and the resultant need for patient dialysis and kidney transplants.
For further information, see: “Interpreting
urine dipstick tests in adults: a reference guide for primary care”, BT (Jun, 2013) and “The detection and management
of patients with chronic kidney disease in primary care”, BPJ 66 (Feb, 2015).