Most of this protein is albumin and Tamm Horsfall protein with
smaller amounts of immunoglobulins.- False positive proteinuria by dip stick occurs mainly when urine is
alkaline and very concentrated; or if the stick test is left in urine for
long time.
False negative proteinuria is observed when protein excretion is
mainly Bence Jones proteinuria and when urine is very diluted. - Bence Jones protein which is the light chain fraction of
immunoglobulin appears in abnormal amounts in urine in cases of
multiple myeloma, clots at temperature 45-55°C, above and below
that range it dissolves in urine. Presence of Bence Jones proteinuria
should be confirmed by immunoelectrophoresis. - The causes of Bence Jone's proteinuria include: multiple myeloma,
amyloidosis, adult Fanconi syndrome, benign monoclonal
gammopathy and hyperparathyroidism.
Mechanism of proteinuria:
There are four known mechanisms for proteinuria. These are:
- Abnormality in permeability of the glomerular basement membrane
because of glomerular disease or abnormal glomerular
hemodynamics. - Increased concentration of small molecular weight protein in blood
(MW 60000- 70000) e.g. hemoglobin, myoglobin and
immunoglobulin light chains. These will pass easily through the
normal GBM - Tubular disease with inadequate reabsorption of normally filtered
proteins of MW <60000 e.g. B2-microglobulin. - Secretion by renal tubular cells of Tamm-Horsfall protein (urinary
glycoprotein).