Laboratory of Forensic Services
Serology Manual
Sacramento County District Attorney
Sero: Urea Presumptive Test for Urine
Urea is the chief product of protein metabolism and is found in high
concentrations in urine.
Principle
Equipment and
Supplies
ve
d
A small cutting of suspected urine stain is placed on a piece of filter paper
with a drop of the acid/base indicator bromothymol blue dried on it. If urea is
present in the suspected stain, the addition of urease will cause the release of
ammonia. Ammonia raises the pH on the filter paper, changing the
bromothymol blue indicator from yellow to blue.
This procedure uses the following laboratory equipment and supplies:
balance
filter paper
Pasteur pipettes.
This procedure uses the following reagents:
Reagents
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i
Bromothymol Blue Solution (10 mL)
Dissolve 40 milligrams of bromothymol blue in 10 mL of deionized water.
Urease Solution (4 mL)
Ar
Dissolve 10 milligrams of urease in 4 milliliter of deionized water. This
reagent must be made fresh daily.
Quality control
The reagents must be tested on a positive control (urine) and a negative
control (water) each day of use. The results of these tests are recorded in the
case notes.
Sample
preparation
Remove an appropriate sized area of the suspected urine stain.
Continued on next page
Title:
Approved by:
Issue Date:
Sero: Urea Presumptive Test for Urine
Laboratory Director
04/2009
Revision No:
Document Class:
0
LFS Policy/Procedure
All printed copies are uncontrolled. This document printed on 3/31/2015
Page 1 of 2
Laboratory of Forensic Services
Serology Manual
Sacramento County District Attorney
Sero: Urea Presumptive Test for Urine, Continued
Use the following procedure to test for urea.
Step
1
2
3
Action
Place one drop of Bromothymol Blue Solution on a piece of
filter paper, allow to dry.
NOTE: The treated filter paper can be prepared ahead and kept
frozen.
Put the cutting from the suspected urine stain in the middle of the
dried drop.
Add one drop of Urease Solution over the cutting.
ve
d
Procedure
A blue color indicates a positive test for the presence of urea.
Interpretation
The rapid development of a blue color is interpreted as a positive (+) test and
indicates the presence of urea.
ch
i
The absence of the blue color reaction indicates a negative (-) test for the
presence of urea.
This is a presumptive test for the presence of urine. A positive result does not
confirm the presence of urine.
References
The following references were used in the development of this procedure.
Ar
Biology Methods Manual, Metropolitan Police Forensic Science Laboratory,
1978.
Sourcebook in Forensic Serology, Immunology and Biochemistry, U.S.
Department of Justice, National Institute of Justice 1983.
Title:
Approved by:
Issue Date:
Sero: Urea Presumptive Test for Urine
Laboratory Director
04/2009
Revision No:
Document Class:
0
LFS Policy/Procedure
All printed copies are uncontrolled. This document printed on 3/31/2015
Page 2 of 2