Dear colleague,
See the following references for interference in the benzethonium
method:
Ann Clin Biochem 1990;27:88-9
1989;26:104-5
Clinical Chemistry 1988;34:1944-5
1987;33:2127-8
Best regards
Raymond Wulkan
Rotterdam-NL
Date sent: Tue, 19 Oct 1999 12:15:35 -0400
Subject: Interference in urine proteine assay ?
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Dear colleagues,
We have been using the Roche benzethonium chloride method for urinary protein on
a Hitachi 917 (run as a rate assay) successfully for quite a while but recently
ran into a problem.
We measured 1.97 g/L of protein on a patient who also happened to have a request
for urine protein electrophoresis. The sample was concentrated 50fold but gave a
faint protein pattern not compatible with the expected protein concentration. A
subsequent dipstick reading was 0.3 g/L. Diluting the sample two and fourfold
gave 1/2 and 1/4 of the original concentration by benzethonium, as expected. We
then sent the sample to two other labs and got 0.2 g/L with the sulfosalicylic
acid method and 0.58 g/L with the pyrogallol method.
Interestingly, the patient had shown a discrepancy between the benzethonium and
the dipstick method four weeks earlier already (1.45 g/L vs 0.3 g/L) but had
much more compatible results ( 0.08 g/L vs negative protein) five weeks earlier.
The only interference listed for the assay is hemoglobin at > 50 mg/dL but the
urine was yellow and the dipstick was negative for blood. When I called Roche
they had no other information on interferences on file.
The patient was on antibiotics, though, some of which interfere in other urine
protein assays. He was using Azithromycin, Trimethoprim and Sulfamethoxazole. He
was also on Colchicine, Sucralfate, Docusate, and Prednisone, unlikely
candidates for interference. He's off his antibiotics now and expected back soon
for another urine sample.
Has anyone else seen interference in this assay ?
Many thanks
***********************************************************
Wolfgang Schneider
Division of Medical Biochemistry, Montreal General Hospital
1650 Cedar Avenue, Montreal, Quebec H3G 1A4, Canada
Phone (514)-937-6011 x 2782 Fax (514) 934-8086
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Email at home: [log in to unmask]
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