A31(W)
A COMPARISON OF ACR AND PCR MEASUREMENT IN THE DETECTION OF
PROTEINURIA
Lamb, E 1 McTaggart, M1 Pinnock, R2 Price, C3 Newall, R4, Stevens, P5
1
Department of Clinical Biochemistry and the 5Kent Kidney Care Centre,East Kent
Hospitals University NHS Foundation Trust, Canterbury, 2North Street Surgery, Ashford,
Kent, 3Department of Clinical Biochemistry, University of Oxford, Oxford, and
4
Amersham, Buckinghamshire
Proteinuria is routinely detected by measurement of the urinary albumin- and/or protein-tocreatinine ratio (ACR/PCR). There is debate concerning whether the ACR or PCR is the more
reliable indicator of protein loss.
We have assessed causes of discordance between the measured ACR and PCR in patients with
chronic kidney disease (CKD) and those at risk of developing CKD, e.g. patients with diabetes
mellitus or hypertension. ACR (immunoturbidimetric urinary albumin method) and PCR
(benzethonium chloride urinary total protein method) were measured in 297 patient samples: 18
(6%) of these samples had a normal ACR (<3.4 mg/mmol) but raised PCR (>23 mg/mmol) by
USA Kidney Disease Outcome Quality Initiative thresholds. The nature of the proteinuria was
investigated in these ‘discrepant’ samples which were retained for further laboratory analyses.
This analyses included repeat albumin and total protein measurement, examination using SDSAGE, assays for ‘tubular proteins’ and the use of alternative albumin and total protein methods.
Only a trace of albumin was visible in the discrepant samples following SDS-AGE. Neither
cystatin C nor beta trace protein was detectable in any of the samples, although the alpha-1microglobulin-to-creatinine ratio was slightly above the reference range of 1.5 mg/mmol in
seven of the samples (highest was 5.9 mg/mmol). Repeat measurement of albumin did not
result in reclassification of any of the samples from normoalbuminuric to albuminuric, whilst
the repeat measurement of total protein resulted in the reclassification of one proteinuric sample
to non-proteinuric. Use of an alternative method to measure albumin (immunonephelometric)
did not affect sample classification. However, when an alternative total protein method
(pyrogallol red) was used, eleven of the discrepant samples were reclassified from proteinuric to
non-proteinuric.
Analytically, ACR appears to be a more reliable indicator of proteinuria than PCR.
Classification of proteinuria based on PCR was dependent on the chemical method used.