The problems of proteinuria measurement in urine with presence of Bence Jones protein
ABSTRACT Protein concentration measurement in the urine can be problematic in the presence of Bence Jones protein. We have carried out an external quality control assessment with the participation of 79 clinical biochemistry laboratories from the Czech Republic and Slovakia.
The laboratories received a reference urine sample obtained from a patient with multiple myeloma and lambda free light chain proteinuria and were asked to type the paraprotein using immunofixation and to measure total urinary protein using their established method, most commonly turbidimetry, pyrogallol red assay, and biuret assay.
There was a very wide inter-laboratory variability in the protein concentration readouts with up to three-fold difference in some cases. High-resolution two-dimensional electrophoresis and linear mass spectrometry showed that a high proportion of the urinary paraprotein was composed of lambda light chain fragments with molecular weight of 12kDa.
Our results highlight the challenges of reliable and reproducible measurement of urinary protein concentration in the presence of Bence Jones protein.
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ABSTRACT: Permanent proteinuria is an early marker of the kidney dysfunction. Tracking by urinary strip, imposes a precise quantification by the laboratory. In front of the difficulties of urine collection during 24 hours, protein determination can be carried out on the urine of a miction and can be expressed as g per g of creatinine (uPCR). We analysed the impact of the expression of the proteinuria in g/L (uP) as compared to uPCR on the urinary electrophoretic profiles. A revision and a simplification of this in practice clinical interpretation is proposed. The proteinuria of 696 in-patients was quantified on an Olympus AU2700. The urinary electophoretic profiles (SDS-AGE) were interpreted by two biologists. uP and uPCR are well correlated (r=0.847, p< 0.0001). Data agreed for proteinuria > 1 g/L but concordance was obtained only in 74% of the subjects and 55% of the pathological patients. A repetition of the analyses is suggested. The interpretative diagram suggested with simplified comments improved interpretation. We advise an interpretation by two biologists. In conclusion, interpretation of the urinary electrophoretic profile rests on the rate of total proteinuria. Expression of the proteinuria as g/g of creatinine must be associated with the expression in g/L because of the analytical conditions. The SDS-AGE Technique does not allow the identification of the monoclonal compound but allows a quantitative follow-up under treatment and especially an early tracking of the type of renal dysfunction.12/2013; 71(6):667-678. DOI:10.1684/abc.2013.0913
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ABSTRACT: Preeclampsia is a pregnancy-specific disorder of unknown etiology and a leading contributor to maternal and perinatal morbidity and mortality worldwide. Because there is no cure other than delivery, preeclampsia is the leading cause of iatrogenic preterm birth. We show that preeclampsia shares pathophysiologic features with recognized protein misfolding disorders. These features include urine congophilia (affinity for the amyloidophilic dye Congo red), affinity for conformational state-dependent antibodies, and dysregulation of prototype proteolytic enzymes involved in amyloid precursor protein (APP) processing. Assessment of global protein misfolding load in pregnancy based on urine congophilia (Congo red dot test) carries diagnostic and prognostic potential for preeclampsia. We used conformational state-dependent antibodies to demonstrate the presence of generic supramolecular assemblies (prefibrillar oligomers and annular protofibrils), which vary in quantitative and qualitative representation with preeclampsia severity. In the first attempt to characterize the preeclampsia misfoldome, we report that the urine congophilic material includes proteoforms of ceruloplasmin, immunoglobulin free light chains, SERPINA1, albumin, interferon-inducible protein 6-16, and Alzheimer's β-amyloid. The human placenta abundantly expresses APP along with prototype APP-processing enzymes, of which the α-secretase ADAM10, the β-secretases BACE1 and BACE2, and the γ-secretase presenilin-1 were all up-regulated in preeclampsia. The presence of β-amyloid aggregates in placentas of women with preeclampsia and fetal growth restriction further supports the notion that this condition should join the growing list of protein conformational disorders. If these aggregates play a pathophysiologic role, our findings may lead to treatment for preeclampsia.Science translational medicine 07/2014; 6(245):245ra92. DOI:10.1126/scitranslmed.3008808 · 14.41 Impact Factor