Point of Care Testing:
Vaginal pH
Eberhard Fiebig, MD
Director, SFGH Clinical Laboratory
Purpose (Indications)
pH Testing is Helpful in the Diagnosis of:


ruptured amniotic
membranes in
pregnancy
bacterial vaginosis
and trichomonas
infection
Ruptured Membranes
Bacterial Vaginosis
Principle
pH Paper Strips…

Fluid from the upper vagina is normally acidic (pH
3.8-4.5)

Leakage of amniotic fluid (normal pH 7.0-7.5) OR
bacterial overgrowth raises the pH to >4.5


The pH paper is impregnated with the dye nitrazine
(phenaphtazine) which changes color from yellow
to blue as pH increases from 4.5 to ≥ 7.0
Changes in color shades occur in pH increments of
0.5, allowing semiquantitative pH measures when
the color of the pH paper is compared to a
standard color chart supplied with each roll of pH
paper
…at pH 4.0 and 7.0
Sample

Pooled vaginal fluid sampled with a
cotton swab during speculum
examination
Testing



Apply cotton tip soaked in
vaginal fluid to pH paper
Observe the paper for
immediate color change
by comparing to the color
chart in the dispenser
Record pH value
corresponding to the color
chart
Quality Control




Quality control (QC) of pH paper is performed
by the Clinical Laboratory on shipment
samples before release.
QC consists of verification of the appropriate
color reaction against certified buffer
solutions.
Verified papers will be given an expiration
date of 1 year from QC. The expiration date is
printed on a label attached to each paper roll
dispenser.
pH Paper without expiration date label on the
dispenser or pH paper past the expiration
date MUST NOT BE USED.
Expiration Date on Dispenser
Limitations


False positive (elevated) pH values may occur
due to alkalinization of the vagina by blood,
semen, urine, soap, antiseptic solutions,
antibiotic therapy and infections.
False negative pH values (failure to detect
elevated pH as a result from ruptured
membranes) may occur due to decreased efflux
of amniotic fluid as the time between membrane
rupture and testing increases.
Are You Color Fit?

Interpretation of vaginal pH test results
may be affected by poor color vision.

Up to 10% males and 0.4% females may
be color deficient to some degree.


Everyone should see “12”
If you have not done so already, have your
color vision checked if you perform point of
care tests or other tasks that require color
discrimination.
New employees are color tested as part of
the orientation process. Existing employees
should make an appointment with SFGH
Clin Lab’s POCT services (206-8588).
Persons with normal color
vision should see “26”
References


Simoes JA, Discacciati MG, Brolazo EM,
Portugal PM, Dini DV, Dantas MCM. Clinical
diagnosis of bacterial vaginosis. Intl J Gyncol
Obstet 2006;94:28-32.
Davidson, KM. Detection of premature
rupture of the membranes. Clin Obstet
Gyncol 1991;34(4):715-722.
Vaginal pH Quiz
1. Vaginal pH Testing is Intended for:
A. Exact pH measurement of vaginal fluid
B. Aiding in the diagnosis of ruptured membranes in
pregnancy, bacterial vaginosis and trichomonas
infection
C. Exclusion of pregnancy
D. Diagnosis of herpes infection
E. Screening for vaginal bleeding
Vaginal pH Quiz
2. Vaginal pH Measurement is based on:
A.
B.
C.
D.
Color change of pH paper from yellow to red
Color change of pH paper between pH 1.0 – 4.0
Change in color of pH paper from yellow to blue
Random color changes as pH increases
E.
Change in color shade every 2 pH points
Vaginal pH Quiz
3. Vaginal pH Testing is performed by:
A.
B.
C.
D.
E.
Collection of vaginal fluid by cotton swab during
speculum exam.
Touching the pH paper with cotton tip containing
collected vaginal fluid.
Observing pH paper for immediate color change by
comparing to standard color chart.
Recording the pH value, corresponding to the color
change in the patient’s chart.
All of the above is correct.
Vaginal pH Quiz
4. Quality Control of the Vaginal pH Test
A.
B.
C.
D.
E.
Is performed by the Clinical Laboratory
Consists of verifying the performance of a sample of pH
paper against certified buffer solutions
Is documented by the Clinical Laboratory through placing
a label with an expiration date on individual pH paper
dispensers
Allows the pH paper to be used until the expiration date
which is 1 year from when QC was performed
All of the above is correct
Vaginal pH Quiz
5. Limitations of Vaginal pH Testing include
A.
B.
C.
D.
E.
pH paper does not work very well in the relevant range
between pH 4.0 and 7.0
It takes a while for pH paper to change color after
coming in touch with vaginal fluid
pH paper is only useful for detecting ruptured
membranes in pregnancy
False elevation of vaginal pH may be caused by urine,
blood, semen, soap and antiseptic solutions
All of the above are correct