General consideration Urine analysis is an essential component in the investigation of patients with
paraproteinaemia or with suspected B cell malignancies. An important feature
used to help distinguishing malignant from non-malignant conditions is the finding
of immunoglobulin fragments produced by tumour cells. The fragments, which may
not be detectable on serum electrophoresis separations, are usually of lower
molecular weight than intact immunoglobulin molecules. These fragments pass readily
through the kidney, and may be clearly visible in the urine due to the concentration
effect. The finding of Bence-Jones proteins (BJP) therefore provides a high index
of suspicion for malignancy, although it does occur in apparently benign conditions.
Even low concentrations (10mg/l) may be significant and therefore concentrated
urine (at least 100-fold concentration of early-morning urine is preferable)
must be run in the serum systems. Whatever system is used, a trace of albumin
must be visible in all urine samples; if this is not the case, the sample should
be re-run or further concentrated. Where a BJP
is present in significant concentrations (>100mg/l) with no
accompanying glomerular or tubular proteinuria, detection is straightforward
and the immunofixation
identification step is unequivocal. However, the renal damage associated
with BJ proteinuria, frequently results in complex, non-standard
patterns requiring
immunofixation to resolve the possible presence of BJP. A low concentration
of BJP may also accompany significant glomerular proteinuria in
patients with light chain renal amyloidosis; the urine of any such
patient
should be investigated by immunofixation even in the absence of a band
suggestive of BJP. Patients with serum paraproteins may show a "leak" of
the serum paraprotein into the urine. This may occur with or without
Bence Jones
protein
and immunofixation is essential to distinguish these. A number
of other proteins may appear as discrete bands on urine electrophoretic
separations, particularly where there is an element of tubular proteinuria.
These include the a- and ß-microglobulins, lysozyme (migrating in the slow gamma
region), degraded fragments of glomerular origin and rarely seminal fluid proteins.
In some samples the ß2-microglobulin will be present in high concentrations
and give a very prominent band. Normal Values • Protein
is not normally found in large quantities in the urine. What abnormal results mean Special
considerations Drugs that can affect the measurement of proteins
include chlorpromazine, corticosteroids, isoniazid, neomycin, phenacemide,
salicylates, sulfonamides, and tolbutamide. Never discontinue any
medication without consulting your health care provider.
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