Specific gravity is a measurement of urine density that reflects the kidney's ability to concentrate or dilute urine. It depends on the amount of solutes in the urine. The specific gravity of normal urine ranges from 1.003 to 1.030. An increased specific gravity indicates conditions like dehydration, diabetes, or kidney disease that cause higher solute concentration, while a decreased specific gravity suggests diabetes insipidus or kidney failure. Specific gravity can be measured using a urinometer, refractometer, or reagent strips and provides important information about a patient's hydration status and kidney function.

1. SPECIFIC GRAVITY
OF URINE AND ITS
SIGNIFINACE
DR.ABHINAV GOLLA
MEDICURE DIAGNOSTICS AND
RESEARCH CENTER
VIJAYANAGAR COLONY, HYDERABAD,
TELANGANA.

2. DETAILS
• Introduction
• Composition of urine
• Indication of urine analysis
• Collection of urine sample
cont…

3. •Changes which occur in
standing urine at room
temperature
•Chemical preservatives
•Specific gravity of urine

4. INTRODUCTION
•Urine analysis is one
of the most
commonly performed
laboratory tests in
clinical picture.

5. COMPOSITION OF URINE
•Volume – 600-2000ml
•Specific gravity-1.003-
1.030
•Osmolality – 300-900
mOsm/kg
•Ph – 4.6-8.0

6. • Proteins - <150 mg
• Urobilinogen -0.5 – 4.0 mg
• Porphobilinogen – 0 – 2 mg
• Creatinine – 14-26mg/kg (male)
11-20mg/kg (female)
cont..

7. •Urea nitrogen -12-20mg
•Uric acid – 250-750mg
•Sodium -40-220mEq
•Potassium- 25-125mEq
cont…

8. •Chloride – 110-250mEq
•Calcium – 50-150 mg
•Formiminoglutamic acid (FIGLU)-
<3mg
•Red cells , epithelial cells , WBC-
</=1-2cells/high power
field

9. INDICATIONS FOR URINALYSIS
• Suspected renal diseases like
glomerulonephritis , nephrotic
syndrome , pyelonephritis and renal
failure
• Detection and management of UTI
cont…

10. • Differential diagnosis of
jaundice
• Detection and management
of plasma cell dyscrasis
• Diagnosis of pregnancy

12. CHANGES AT ROOM
TEMPERATURE
•Increase in ph
•Formation of crystals
•Loss of ketone bodies
•Decrease in glucose
cont…

13. • Oxidation of bilirubin to biliverdin
• Oxidation of urobilinogen to
urobilin
• Bacterial proliferation
• Distintegration of cellular elements

14. DO’S AND DONT’S
• Urine sample must be tested in the
lab with in 24hrs of collection.
• Refrigerated (4-6°C) is best general
method of process upto 8 hrs
• For routine urine analysis
perservatives should be avoided

15. CHEMICAL PRESERVATIVES
•HCL
•Toulene
•Boric acid
•Thymol
•Formalin

16. PHYSICAL EXAMINATION
• PARAMETERS:
• Volume
• Color
• Appearance
• Odor
• Specific gravity
• Ph

17. SPECIFIC
GRAVITY

18. DEFINITION
•It is the measurment of urine density
which reflects the ability of the
kidney to concentrate or dilute the
urine relative to the plasma from
which it is filtered .
•Also called as RELATIVE MASS
DENSITY.

19. • It depends on the amount of
solutes in a solution.
• It is basically a comparision of
density of urine against that of
distilled water at particular
temperature.

20. • SG of distilled water is 1.000
• SG of urine is 1.003-1.030
(depends on the state of hydration)
• SG of normal urine is mainly related to urea
and sodium .
• SG , osmolality , urine color are reliable
indicators of hydration status.

21. INCREASE OF SPECIFIC GRAVITY
• Diabetes mellitus (glucosuria )
• Nephrotic syndrome ( proteinuria )
• Fever
• Dehydration
• Adrenal insufficiency
• Congestive heart failure
• Hepatic diseases.

22. DECREASE OF SPECIFIC GRAVITY
•Diabetes insipidus (SG btw
1.002-1.003)
•Chronic renal failure .
•Compulsive water drinking .

23. ISOTHENURIA
• When little or no variability of specific
gravity is noted between several specimens
from a patient.
• Specific gravity is fixed and the value is
1.010
• This condition is seen in case of severe
renal damage with disruption of both
concentrating and diluting abilities.

24. METHODS OF MEASURING
SPECIFIC GRAVITY
1. Urinometer
2. Refractometer method
3. Reagent strip method

25. URINOMETER METHOD
• Based on the principle of bouyancy
• Urinometer (hydrometer) is placed in a container filled
with urine .
• When solute concentration is high , uptrust of solution
increases and urinometer is pushed up (high SG )
• If solute concentration is low ,it sinks (low SG)
• Its accuracy needs to be checked with distilled water .

27. PROCEDURE
• Fill a measuring cylinder with 15 ml of urine.
• Lower the urinometer gently into the urine and let it
float.
• Let the urinometer settle , it should not touch the
sides or bottom of the cylinder.
• Take the reading of SG on the scale (lowest point of
meniscus) at the surface of the urine.
• Take out the urinometer and immediately note the
temperature of urine with a thermometer.

28. CORRECTION OF TEMPERATURE
•Density of urine -Increases at low
temperature
decreases at high
temperature
•This causes false reading of
SG.
•Therefore SG is corrected for
difference between urine

29. • Check the temperature and calibration of
the urinometer to get the corrected SG ,
add 0.001 to the reading for every 3°C that
the urine temperature is above the
temperature of calibration.
• Similarly substracted 0.001 from the
reading for every 3°C below the calibration
temperature .

30. CORRECTION OF DILUTION
• If quantity of urine is not
sufficient for measurement of
SG , urine can be appropriately
diluted and the last two figures
of SG are mutliplied by dilution
factor

31. CORRECTION FOR ABNORMAL
SOLUTE CONCENTRATION
• High SG in the presence of
glycosuria or protienuria will not
reflect true kidney function
(concentrating ability ).
• Therefore it is necessary to
nullify the effect of glucose or
protiens .

32. •For this 0.003 is substracted
from temperature corrected
SG for each 1gm of
protien/dlurine and 0.004 for
every 1 gm of glucose/dl
urine

33. REFRACTOMETER METHOD
• SG can be precisely determined by a
refractometer , which measures the
refractive index of the total soluable
solids .
• Higher the concentration of total
dissolved solids , higher the refractive
index .

34. • Extent of refraction of a beam of light passed through
urine to measure the solute concentration and thus
the SG .
• The method is simple and requires only 1-2 drops of
urine .
• Result is read from a scale or digital display.

37. REAGENT STRIP METHOD
• Reagent strip measures the concentration
of ions in the urine , which correlates with
SG
• Reagent has 3 main ingredients –
polyelectrolyte , indicator substance , buffer
• Principle: this is based on th pka change of
pretreated polyelectrolyte inrelation to the
ionic concentration of urine .

38. • Depending on the ionic strength
of urine , a polyelectrolyte will
ionize in proportion.
• This causes a change in color of
Ph indicator ( bromothymol
blue )

40. • Other methods
Harmonic oscillation densitometry
Falling drop method
Both these methods measure specific
gravity
directly.

41. TAKE HOME MESSAGE
Direct method
• Principle – measures density
• Molecular sizes of solutes donot
effect the values.
• All solutes are detected.Indirect method
• Principle - measures
refractive index
Indirect method
• Principle-Measures pka(acid
dissociation constant)
Limitation – measures only ionic
solutes.
Cannot measure non
ionic solutes.
Limitation –results are affected by
molecular size & structure.
Mostly the correction calculation not
done.
Unacceptable accuracy for urine
measurements.disadvantage is more
amount of urine is
required,urinometer is calibrated
daily, temperature correction needed

42. REFERENCES
• Henrys – Clinical diagnosis and management by
laboratory methods.
• Fundamentals of urine & Body fluid analysias – Nancy
A.Brunzel.