Unexpected random urinary protein:creatinine ratio results–limitations of the pyrocatechol violet-dye method

BMC Pregnancy and Childbirth

Laura A Magee¹  Peter von Dadelszen¹  Yasser Sabr⁴  Anne-Marie Côté²  Anne C Halstead³  Dane A De Silva⁴ 

[1] Child and Family Research Institute, University of British Columbia, Vancouver, Canada;Department of Medicine, Université de Sherbrooke, Sherbrooke, Canada;Department of Pathology and Laboratory Medicine, Children’s and Women’s Health Centre of British Columbia and the University of British Columbia, Vancouver, Canada;Department of Obstetrics and Gynaecology, University of British Columbia, Vancouver, Canada

关键词: Laboratory;    Proteinuria measurement;    Protein:creatinine ratio;    Pregnancy;    Pre-eclampsia;    Hypertension;   

Others  :  1137948
DOI  :  10.1186/1471-2393-13-152

 received in 2012-11-06, accepted in 2013-07-07,  发布年份 2013

【 摘 要 】

Background

For clinicians, it is important to rely on accurate laboratory results for patient care and optimal use of health care resources. We sought to explore our observations that urine protein:creatinine ratios (PrCr) ≥30 mg/mmol are seen not infrequently associated with normal pregnancy outcome.

Methods

Urine samples were collected prospectively from 160 pregnant women attending high-risk maternity clinics at a tertiary care facility. Urinary protein was measured using a pyrocatechol violet assay and urinary creatinine by an enzymatic method on Vitros analysers. Maternal/perinatal outcomes were abstracted from hospital records.

Results

91/233 (39.1%) samples had a PrCr ≥30 mg/mmol, especially when urinary creatinine concentration was <3 mM (94.1%) vs. ≥3 mM (16.4%) (p < 0.001). When using the last sample before delivery, 47/160 (29.4%) had a PrCr ≥30 mg/mmol in diluted urine vs. only 17/160 (15.4%) in more concentrated urine (p < 0.001); PrCr positive results were also more frequent among the 32 (20.0%) women with known normal pregnancy outcome (90.9% vs. 0) (p < 0.001). Using the same analyser, 0.12 g/L urinary protein was ‘detected’ in deionised water. Re-analysis of data from two cohorts revealed substantially less inflation of PrCr in dilute urine using a pyrogallol red assay.

Conclusions

Random urinary PrCr was overestimated in dilute urine when tested using a common pyrocatechol violet dye-based method. This effect was reduced in cohorts when pyrogallol red assays were used. False positive results can impact on diagnosis and patient care. This highlights the need for both clinical and laboratory quality improvement projects and standardization of laboratory protein measurement.

【 授权许可】

   
2013 De Silva et al.; licensee BioMed Central Ltd.

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