Patho Lab

     Urinometer method

     Principle

Specific gravity is a function of the number, density and weight of the solute particles present and is used as a measure of the concentrating power of the kidney. The specific gravity of urine is its density compared with the density of distilled water that is conveniently fixed as 1.000 at 200C.

It ismeasured using a weighted cylinder called "urinometer", which floats in the urine and which is calibrated against distilled water at 20° C. Check the working of the urinometerby floating it in distilled water to see if the reading is 1.000. As the specific gravity varies with temperature, apply temperature correction before reporting.

      Procedure

     Pour about 40 - 50ml of urine into a 100ml glass measuring cylinder.

     lower the urinometer gently into the urine, rotate and release (avoid frothing).

     Wait for the urinometer to settle (make sure that the urinometer does not come into contact with the sides or bottom of the cylinder).

     Read the specific gravity given on the scale at the surface of the urine (use the lower point of the meniscus for reading).

     Observe the temperature of the urine.

     Result

Check the temperature at which the urinometer is calibrated. It is usually at 200C. For every 30C that the urine temperature is above the calibration temperature, add 0.001 to the measured specific gravity and for every 30C that the urine temperature is below the calibration temperature, subtract 0.001 from the measured specific gravity.

Example

Urinometer is calibrated at 200C

Urine temperature 230C

The measured specific gravity 1.023

The temperature of urine is 30C higher than the calibration temperature.

\ Specific gravity to be added to the measured specific gravity =

3/3 x 0.001 = 0.003/3 = 0.001.

\ The actual specific gravity = 1.023+0.001=1.024.

     Interpretation and quality control

The normal urine-specific gravity is 1.010 – 1.030

The presence of an increased amount...