Artifactually Low Serum Urea Caused by Antibodies to Bacteria Urease

[摘要] Bacterial or jack bean urease is used for determining urea in serum or urine (1). We encountered a clinical serum sample with an abnormally low urea value as measured with a reagent containing bacterial urease, but with a normal urea as measured with a urea reagent containing jack bean urease. We believed that the low urea value was caused by an inhibitor of bacterial urease activity, potentially an immunoglobulin. Although enzyme-binding human immunoglobulins have been reported for lactate dehydrogenase, alkaline phosphatase, and amylase (2)(3), no cases have been reported of immunoglobulin against non-human urease. To investigate the possible presence of immunoglobulins that bind bacterial urease, we used an ELISA method to react bacterial urease with serum from the patient; we measured the urea after serum IgG was removed by adsorption to protein A.Serum samples obtained on admission and discharge were stored at −20 °C until use. Urea and immunoglobulin were measured with a Hitachi model 7150 analyzer. The urea measurement methods (Iatron) were (a) a colorimetric jack bean urease method with indophenol, (b) a jack bean urease method with glutamate dehydrogenase (GLDH) for ultraviolet detection of generated ammonia, and (c) a bacterial urease method with GLDH. The method (Iatron) for immunoglobulin (IgG, IgA, and IgM) was a turbidimetric immunoassay. The serum was centrifuged in an ultrafiltration unit (Amicon Centrifree) at 1500 g for 10 …

[学科分类] 过敏症与临床免疫学