SPECIFIC GRAVITY

1.000-1.030

Specific Gravity of Urine

pKa change of a polyelectrolyte

principle involved in specific gravity

High protein concentration

Indicates False positive of specific gravity

Methyl Vinyl Ether Malaeic Anhydrided Bromothymol Blue

Reagent used in Multistix in Specific Gravity

Ethyleneglycol DiAminoEthyl Ether Tetraacetic Acid Bromothymol Blue

Reagent used in Chemstrip for Specific Gravity

High Alkaline Urine (>6.5)

(This is when adding 0.005 to the SG, the pH of the urine will be >6.5)

indicates False Negative

• Tempreature of 20C = 1.013 True Value

• Temperature of 17C =62.6 °F corrected value of SG 1.012

Requuired correction SG value

Refractometer

Refractive index refers to the comparison of the velocity of light in air to the velocity of light in solution.

15C-38C

Temperature for Refractometer

LOWER=0.002

Reading of Refractometer compared to Urinometer by 0.002

Harmonic Oscillation Densitometry

• This is where urine enters a glass tube with an electromagnetic coil at one end.

• An older model of the IRIS automated system used HOD

1.080

Validity of result of SG for research purposes

Mass Gravity Meter

It is used b y YELLOW IRIS (International Remote Imaging System)

Multiply the last 2 digits of SG by 2

Formula for Urine Dilution , if the specific gravity is too high to get a reading, then dilution is necessary.

Temperature Correction

Adjusts specific gravity based on urine temperature.

Baseline Value

Standard reference temperature set at 20°C.

Specific Gravity

Density measurement of urine relative to water.

Glucose Correction

Subtract 0.004 for each 1g/dL glucose.

Protein Correction

Subtract 0.003 for each 1g/dL protein.

Refractometer

Device measuring refractive index of urine.

Refractive Index

Velocity of light in a solution.

Polyelectrolyte

Ionizes, releasing H+ ions in urine.

Calibration

Adjusting instruments for accurate measurements.

Alkaline Urine

Urine with pH greater than 6.5.

Distilled Water SG

Standard specific gravity value of 1.000.

Harmonic Oscillation Densitometry

Method using sonic oscillation to measure density.

Electromagnetic Coil

Generates sonic oscillation in HOD system.

Microprocessor

Corrects temperature in harmonic oscillation densitometry.

Mass Gravity Meter

Device used for specific gravity determination.

IRIS Diagnostics

Automated system for urine analysis.

Required Urine Volume

6mL needed for IRIS analysis.

Dilution Method

Used when specific gravity is too high.

Sample Problem

Example calculation for diluted urine SG.

True SG Calculation

Multiply last two digits by 2.

Obsolete Technology

IRIS changed from HOD to refractometry in 2011.