Interlaboratory bias of albuminuria and proteinuria in hypertensive pregnancy

Abstract

Background: Measurement of proteinuria in women with hypertensive disorders of pregnancy is of major importance in the diagnosis and management of preeclampsia. Urinary protein/creatinine ratio, which is commonly used to detect kidney damage in preeclampsia, suffers from important analytical limitations, including poor harmonization of results between laboratories. Adoption of albuminuria could help reduce interlaboratory bias, since methods used to quantify it are better harmonized.

Methods: A total of 27 urinary samples collected from hypertensive women evaluated for preeclampsia were sent to four different clinical laboratories in Canada. Urinary proteins and albumin as well as urinary creatinine were measured in duplicates in one batch to calculate protein/creatinine (PCR) and albumin/creatinine (ACR) ratio. Statistical analyses were done to evaluate interlaboratory variability of urinary proteins and urinary albumin.

Results: Interlaboratory bias for urinary proteins ranged from 64.7% at low concentration to 3.9% at higher concentrations. In contrast, urinary albumin interlaboratory bias ranged from 29.2% to 4% from low to high concentrations. Coefficient of variation for urinary proteins reached a maximum of 91.5% in lower concentration while urinary albumin highest value was 42.7%. When looking at PCR and ACR ratio, eight samples had PCR measurement range that contained the diagnostic threshold used to detect kidney damage in HDP (30 mg/mmol), while only four samples had ACR ratio measurement range that contained the diagnostic threshold used outside of pregnancy in Canada (2 mg/mmol).

Conclusion: Interlaboratory bias was lower for urinary albumin measurement compared to urinary proteins in hypertensive women evaluated for preeclampsia. Better harmonization with the use of albumin instead of protein measurement would reduce instances where results of different laboratories lead to opposite diagnosis of kidney damage in pregnancy.

Keywords: Albumin; Hypertension; Interlaboratory bias; Preeclampsia; Pregnancy; Protein.