Dear Colleagues,
We have previously performed interference studies with bilirubin on
multiple creatinine methods using the Glick method for preparing bilirubin.
This is presumably unconjugated bilirubin we have been using. It seems we
now need to evaluate unconjugated bilirubin.
We recently had a patient with severe liver disease and a bilirubin
(largely conjugated) of about 700 umol/L. A Roche rate-blanked Jaffe
creatinine assay and an Olympus two point Jaffe assay each gave values of
about 0.25 mmol/L. In contrast a Vitros dry-slide enzymatic method gave
values of about 0.14 mmol/L. The patient was on continuous venous dialysis
and the urea was also elevated.
We have no local data on the effects of conjugated bilirubin on any of the
methods. We know that unconjugated bilirubin has little effect on any of
the assays at 700 umol/L. A medline search suggests that the interference
of all forms of bilirubin on the Jaffe reaction is negative. A reference
also suggests that conjugated bilirubin can falsely lower enzymatic
creatininines, presumably by antioxidant activities on the H2O2 prodiced.
Does anyone have experience with the effect of conjugated bilirubin on
Jaffe or enzymatic methods? Does anyone have a source for conjugated
bilirubin for in-vitro studies?
Many thanks,
Graham
Dr Graham Jones
Staff Specialist in Chemical Pathology
St Vincent's Hospital, Sydney
Ph: (02) 8382-9160
Fax: (02) 8382-2489
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