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Unexpected random urinary protein : creatinine ratio results-limitations of the pyrocatechol violet-dye method . 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 .
60520
Intervention_Pharmacological
pyrocatechol violet-dye method
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Participant_Sample-size
160
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Participant_Sex
women
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Participant_Condition
high-risk maternity