Bence Jones proteinuria is the classic example of overflow proteinuria where increased serum concentrations of proteins of low molecular mass are filtered through the glomerulus and exceed the reabsorptive capacity of tubules.
Bence Jones protein should be detected by electrophoresis of urine as passed, or after concentration, depending on the sensitivity of the protein stain used. The test of the adequate sensitivity of the method is that albumin should be visible in all urines studied. Following electrophoresis that demonstrates protein bands in addition to albumin, Bence Jones Protein should be confirmed or excluded by immunofixation.
Dipstick testing for urine protein will NOT detect Bence Jones Protein.
Estimation of the amount of BJP in a 24 hr. urine collection may be of value in the monitoring of BJ-only myeloma, however, the variability in its tubular reabsorption and metabolism by the kidney may make these measurements unrepresentative, particularily at low concentrations of Bence Jones Protein. The value of the test is further compromised by the inherent imprecision of the urine total protein assay (vide infra). A value can be obtained by densitometry of the stained electrophoretic separation and relating this to the total urine protein. When BJP occurs without other overt proteinuria the total protein is an estimate of the BJP.
There is no International Reference Preparation for urinary light chains, and there will be marked variations in reactivity of antisera with monoclonal light chains. For this reason immunochemical methods of quantitation of BJP are not recommended.
See also Monitoring of paraproteins.
Sample requirement: 25 mL urine.
Bence Jones Protein values above 10 mg/L should be considered as potentially malignant. Other references quote 60 mg/L and there are a few well documented reports of concentrations well in excess of these which could not be attributed to B-cell malignancy.