8.2.3 Sulphosalicylic Acid Test
Sulphosalicylic acid is an anionic protein precipitant; it reacts with protein cations
and causes precipitation.
8.2.3.1 Reagent
Three percent aqueous solution of sulphosalicylic acid.
8.2.3.2 Procedure
Mix 1 ml of urine with 3 ml of sulphosalicylic acid. Presence of turbidity or white
precipitate indicates proteins. Uric acid may give false positive test. To rule out this
possibility, the sample is heated; if it becomes clear, proteins are absent and turbidity
is due to uric acid.
8.2.4 Nitric Acid Ring Test (Heller’s Test)
8.2.4.1 Reagents
Conc. HNO 3.
8.2.4.2 Procedure
Layer the urine carefully over few ml of conc. HNO 3 in a test tube so as to get a sharp
line of demarcation. Proteins give a white color ring at the junction offluids.
However, urea, uric acid, and iodinated organic compounds used for X-rays of the
urinary tract can give false positive test.
8.2.5 Bence-Jones Proteins
Bence-Jones proteins are light chains of immunoglobulins which precipitate at low
temperature. The excretion of Bence-Jones proteins in urine is associated with
multiple myeloma and malignant lymphoma. Bence-Jones proteins are synthesized
by malignant plasma cells. There are three qualitative tests to indicate the presence of
Bence-Jones proteins.
8.2.5.1 Harrison’s Test
Principle
Bence-Jones proteins coagulate at temperature from 40 to 60C, but the precipitated
proteins dissolve at the boiling point (80– 100 C). Subsequent cooling to 40– 50 C
reprecipitates the proteins.
Procedure
Add urine to 3/4 of test tube and add few drops of 33% acetic acid. The temperature
is increased up to 40– 60 C. Bence-Jones proteins get precipitated. If the temperature
8.2 Tests for Urinary Proteins 35