Bence Jones proteinuria: why the dipstick misses it
9-year-old German Shepherd with lethargy and lumbar pain. Radiographs show punched-out lytic lesions in several vertebrae. Results:
| Parameter | Result | Reference |
|---|---|---|
| Total protein (serum) | 10.8 g/dL | 5.5–7.5 |
| Albumin | 2.6 g/dL | 2.6–4.0 |
| Globulins | 8.2 g/dL | 2.5–4.5 |
| Urine specific gravity | 1.018 | — |
| Urine pH | 6.0 | 5.5–7.5 |
| Protein (dipstick) | Negative | Negative |
| Sulfosalicylic acid | 3+ | Negative |
What explains the discrepancy?
chevron_right Show answer and explanation
A. False-positive sulfosalicylic acid test due to alkaline urine
Alkaline urine causes false positives on the dipstick, not the sulfosalicylic acid test, and the pH here is 6.0. False positives with sulfosalicylic acid come from iodinated contrast or some antibiotics.
B. Urine too dilute for the dipstick to detect albuminuria
At a specific gravity of 1.018 the urine is not particularly dilute, and albuminuria strong enough to give 3+ with sulfosalicylic acid would also be dipstick-positive.
C. The dipstick mainly detects albumin and barely free light chains
Correct. The dipstick indicator (tetrabromophenol blue) is far more sensitive to albumin than to globulins and light chains. Sulfosalicylic acid precipitates all proteins, so it detects Bence Jones protein; confirm with urine electrophoresis and immunofixation.
D. Renal amyloidosis with glomerular proteinuria underestimated by the dipstick
Glomerular proteinuria is mainly albumin, exactly what the dipstick detects best. A negative dipstick with 3+ sulfosalicylic acid points to proteins other than albumin.
lightbulb Key takeaway
When myeloma is suspected, do not rely on the dipstick: use sulfosalicylic acid and urine electrophoresis/immunofixation. Bence Jones protein occurs in a proportion of canine myelomas and, together with bone lysis, marrow plasmacytosis and a paraprotein, supports the diagnosis.
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Updated: November 1, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.