Interference with serum indices measurement, but not chemical analysis, on the Roche Modular by Patent Blue V

Ann Clin Biochem 2008;45:289-292
© 2008 Association for Clinical Biochemistry


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Original Articles

Denise Darby and
Christopher Broomhead

Department of Clinical Biochemistry, Wythenshawe Hospital, Manchester M23 9LT, UK

Corresponding author: Dr Denise Darby. Email: denise.darby{at}

Background: Patent Blue V is an inert dye increasingly being used duringcancer surgery to identify the sentinel lymph node. We recentlydiscovered three cases with falsely elevated lipaemic indiceson the Roche Modular, following intramammary injection of PatentBlue. This, and other potential interferences by Patent Blue,is examined in this study.

Methods: Serum samples which visually appeared normal, haemolysed oricteric were spiked with Patent Blue to a concentration of 7.3mg/L and the effect on the lipaemic, haemolysis and ictericindices and routine chemical analyses (sodium, potassium, urea,creatinine, bilirubin, alanine aminotransferase, gamma-glutamyltransferase,aspartate aminotransferase, magnesium, creatine kinase, lactatedehydrogenase, amylase, albumin, calcium and phosphate) undertaken.Dose-response curves in the range of 4.9 mg/L to 22.7 mg/L ofPatent Blue were established for normal, icteric and haemolysedpooled serum samples.

Results: Significant positive interference by 7.3 mg/L of Patent Blue was observed in the lipaemic index, with an increase of 149 ± 6.3 (mean ± standard deviation [SD]; P < 0.001). Significant negative interference was observed in both the haemolysis and icteric indices, with decreases of 71 ± 9.7 (P < 0.001) and 46 ± 8.9 (P < 0.001), respectively.Patent Blue had a linear dose-response effect on the serum indices.No significant differences were observed in the chemical analysesassessed.

Conclusions: The effects observed on the Roche Modular serum index measurementswith Patent Blue raises the novel concept of interference inmethods routinely used to detect interference. Despite PatentBlue having no direct effect on chemical analysis, failure toreliably detect potential interference, particularly haemolysis,may lead to misleading results being issued.

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