<Very Good Health Hospital>
Specific Gravity Procedure, Refractometer
The Total Solids (T.S.) meter is a refractometer that is
specifically designed to measure the total solids in solution.
It actually measures the refractive index of the solution but
has a calibrated scale to give a reading for specific gravity.
The refractive index is the ratio of the velocity of light in
air to the velocity of light in solution. The refractive index
varies with temperature but the T.S. meter is temperature
compensated. It contains a liquid in a sealed chamber in the
optical path which also has a refractive index change with
temperature change, thus compensating for the change in
refractive index of the sample. The refractometer is
calibrated to give results in terms of specific gravity, valid
for urine only, not other salt or glucose solutions.
A few drops of fresh urine is preferred. If testing cannot
be performed within 1 hour, refrigerate the specimen at 2o-8o
- Distilled water.
- Urine controls. Refer to the manufacturer’s storage and
use instructions and assayed values.
- Transfer pipets
- Lens paper
Calibration is confirmed by testing with distilled water
and commercial urinalysis controls. All control specimens must
be processed in the same manner as patient samples.
- Test the refractometer with distilled water. The reading
should be 1.000 +/- .001. Record this value on the Specific
Gravity QC log sheet.
- Process the commercial urinalysis controls. Record the
values on the Specific Gravity QC log sheet. If the results
fall outside the acceptable range, repeat the procedure. If
they are still unacceptable, do not report patient results
and notify the Point-of-Care Coordinator. Suspend the use of
the refractometer until the problem is resolved.
- Clean the surface of the cover and prism of the
refractometer with a dampened piece of lens paper and then
dry with lens paper.
- Close the cover.
- With a dropper, place one or two drops of specimen on the
(at the notched bottom of the cover). Capillary action
causes the specimen to flow over the prism surface.
- Holding the refractometer in a horizontal position, turn
toward a bright light.
- Rotate the eyepiece until the specific gravity scale is in
- Read directly on the specific gravity scale at the point
where the dividing line between bright and dark fields
crosses the scale. The scale reads from 1.000 to 1.035 in
increments of 0.001.
- Record the results on the Specific Gravity QC/Patient
sheet as well as the clinical daily flow sheet.
- Dry the refractometer with lens paper between addition of
- When readings are completed, dry the refractometer, add a
drop of distilled water to cleanse the prism and dry with
CARE OF REFRACTOMETER:
- Never touch the prism with anything other than specimen or
- Always apply specimens to the refractometer with the
plastic prism cover in the closed position.
- Never expose the refractometer to temperatures above 65o
- The instrument can be damaged by immersion of the eyepiece
and the focusing ring in water.
Expected Range: 1.000-1.035
Specific gravity is always reported to the third decimal
place. Report the specific gravity as read on the
refractometer scale. If the specific gravity is greater than
1.035 report as >1.035.
- Strasinger, S.K. Urinalysis and Body Fluids, FA Davis Co.,
- Cambridge Instruments TS meter, Optical Systems Division,
Buffalo, NY, 1988.
February 1999 by <Very Good Point of Care
Coordinator>, Point-of-Care Coordinator
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