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December 2000

Procedure:  Specific Gravity Procedure, Refractometer
Product: Total Solids Refractometer
State:  Pennsylvania
Accrediting organization: CAP
NCCLS format:Yes

Point-of-Care testing

<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 C.

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    1. Distilled water.
    2. Urine controls. Refer to the manufacturer’s storage and use instructions and assayed values.


    1. Refractometer
    2. Transfer pipets
    3. 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.

    1. Test the refractometer with distilled water. The reading should be 1.000 +/- .001. Record this value on the Specific Gravity QC log sheet.
    2. 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.

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    1. Clean the surface of the cover and prism of the refractometer with a dampened piece of lens paper and then dry with lens paper.
    2. Close the cover.
    3. With a dropper, place one or two drops of specimen on the prism surface
    4. (at the notched bottom of the cover). Capillary action causes the specimen to flow over the prism surface.

    5. Holding the refractometer in a horizontal position, turn toward a bright light.
    6. Rotate the eyepiece until the specific gravity scale is in focus.
    7. 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.
    8. Record the results on the Specific Gravity QC/Patient sheet as well as the clinical daily flow sheet.
    9. Dry the refractometer with lens paper between addition of each specimen.
    10. When readings are completed, dry the refractometer, add a drop of distilled water to cleanse the prism and dry with lens paper.

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    1. Never touch the prism with anything other than specimen or lens paper.
    2. Always apply specimens to the refractometer with the plastic prism cover in the closed position.
    3. Never expose the refractometer to temperatures above 65o C.
    4. 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.


    1. Strasinger, S.K. Urinalysis and Body Fluids, FA Davis Co., Philadelphia, 1994.
    2. Cambridge Instruments TS meter, Optical Systems Division, Buffalo, NY, 1988.

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Prepared: February 1999 by <Very Good Point of Care Coordinator>, Point-of-Care Coordinator

Medical Director



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