Mantoux Tuberculosis Skin Test Facilitator Guide
Return to Mantoux TB Skin Test Facilitator
Guide Main Page
Part Two: Reading the Mantoux Tuberculin Skin Test
|
19:02 |
The last part of the procedure is to read the Mantoux tuberculin
skin test. The method demonstrated in this videotape is based on
the palpation method. The steps include collecting supplies; inspecting
the site; palpating, marking, and measuring the induration; and
recording the measurement.
There are several different methods for reading the Mantoux tuberculin
skin test, and they can vary among facilities. For each facility,
everyone reading the skin test should receive training in and use
the same method.
A great deal of practice is required to achieve consistently reliable
measurements.
The skin test should be read between 48 and 72 hours after the
skin test has been administered.
A patient who doesn't return within 72 hours will probably need
to be rescheduled for another skin test.
To begin, collect the following supplies: a small, plastic, flexible
ruler marked in millimeters to measure the test, a pen to mark the
edges of the induration, and an alcohol pad to clean off the pen
marks. You'll need the patient's record or other appropriate forms
for documenting the measurement results.
|
A sharp eyeliner pencil and baby oil can be substituted
for the pen and alcohol pad, to remove the marks easily. This
is especially useful if blinded duplicate readings are done
as part of quality control. |
Also have culturally appropriate patient education materials available
for the patient to reinforce information that is explained to the
patient, help answer questions, and provide information on follow-up
evaluation.
|
Patient education materials are available from CDC and
the National TB Model Centers (see Appendix
C). In addition, the National
Prevention Information Network provides access to a TB
Resource Guide that has information about where to find
TB educational materials and other resources. Discuss the
utility of sharing appropriate patient education materials
with the patient prior to placing the test as well as prior
to reading the test.
|
To locate the skin-test site, inspect the arm in good light and
on a firm surface. When the site is on the forearm, turn the arm
palm up, support it, and slightly flex it at the elbow.
The basis of reading the skin test is the presence or absence of
induration, which is a hard, dense, raised formation. This is the
area that is measured.
Sometimes the site has erythema, a reddening of the skin that can
also have swelling. The erythema should NOT be measured.
Whatever induration is present at 48 to 72 hours should be measured
and recorded. Only the part of the reaction that can be felt, which
is the induration, is measured, even if there is soft swelling or
redness at the site. Keep in mind there might not be an induration.
Reactions to the tuberculin test at the injection site can range
from no induration to a large, well-defined induration.
In order to feel the induration properly, keep your fingernails
short enough so that they don't protrude beyond the finger.
The induration is not always visible, so you must rely on palpation
with your fingertips to discover if there's induration at the site.
With your fingers together, touch the area lightly with the pads
of your fingertips.
Using a light, gentle motion, sweep the fingertips over the surface
of the forearm in a 2-inch diameter in all four directions to locate
the margins or edges of induration.
|
Explain how the fingertips are swept from north to south,
south to north, east to west, and west to east. Explain that
there should be no pushing or prodding to find the induration,
only gentle sweeping motions.
|
If induration is present, use a zigzag, feather-like touch over
the area of induration to outline the margins of induration. Determining
margins all around the induration helps to find the edges, which
will be measured later.
When palpating for margins, be careful not to confuse a margin
of induration with a margin of muscle on the forearm. To check this,
raise the patient's arm to a 45-degree angle and palpate again.
You should still be able to palpate the margins of induration.
The diameter of the induration is measured across the forearm,
from the thumb side of the arm to the little finger side of the
arm or vice versa.
|
Explain that the orientation of the line of measurement
can be remembered by visualizing the direction in which a
watch-band lies across the arm.
|
To mark the edges of the induration, hold your palm over the injection
site with your fingertips at the outer edge of the patient's forearm.
Without lifting, move the fingertips from the outer edge of the
forearm towards the induration. Rest one fingertip firmly against
the induration margin border on one side before marking the margin.
The fingertip should remain in contact with the skin at all times.
Mark lightly with a fine dot at the widest edge of the induration,
using the fingertip as a guide.
Repeat the procedure from the other side of the patient's forearm
and place the second mark on the margin of induration. Palpate again
to double check that the induration was marked correctly.
If the margin is not equally clear all the way around the induration,
it's still necessary to mark the margins on each side of the induration.
Palpate around the induration from the easily felt margin to the
not-so-easily-felt margin.
If the margins of induration are irregular, mark and measure the
longest diameter across the forearm.
To measure the diameter of the induration, use the millimeter ruler.
Place the zero ruler line inside the left dot edge and read the
ruler line inside the right dot edge. If the measurement falls between
two divisions on the millimeter scale, record the lower mark. The
induration shown here measures 10 mm.
Reactions to the skin test will vary. For example, this is a very
large reaction with blistering, swelling, and redness.
Make sure to record blistering, even if no induration is present.
Palpate this induration gently, as it may be painful. Measure only
the induration.
This reaction measures 17 mm.
There is redness and swelling in this reaction, but there is no
induration. Because only the margins of induration are significant,
the redness and swelling should not be mistakenly measured.
Therefore, the measurement of this induration is 0 mm.
Immediately after the test is measured, write the exact measurement
in millimeters of induration on the patient's record. Do not simply
record the interpretation of the results as "negative"
or "positive," and do not record the results in centimeters.
For example, an induration that measures 3 mm should be recorded
as "3 mm" and not as "negative." Additional
information should include the date and time the test was read,
the name and signature of the person who read the skin test, and
the presence or absence of adverse effects.
State or local policies may require additional documentation of
adverse effects.
|
Discuss the documentation policies and procedures
in your facility. Share a copy of the documentation form(s)
that is used in your facility. Describe any additional documentation
that may be necessary for reporting adverse effects (e.g.,
MedWatch forms).
|
Accurately reading and recording skin test measurement results
is important and gives the health care provider useful information
for evaluation. Results are often used as a baseline or as a comparison
with past or future test results.
Interpretation should be performed by a trained health care provider
in accordance with institutional policies based on CDC guidelines.
Check your institution's policy for evaluation and referral procedures.
|
Discuss your facility’s policy for interpretation
of the skin test measurement. If interpretation is conducted
by the same person who reads the skin test, discuss cut points
for interpretation (see Appendix
D). If interpretation is conducted by someone else at
your facility, discuss evaluation and referral procedures.
|
Reliable reading of the tuberculin skin test requires a great deal
of practice and adherence to appropriate steps for quality control.
The steps in this method include standardization of procedures,
training, supervision, and practice. This may include periodic standardized
reliability testing.
|
Discuss the opportunities available for additional
practice and training on the Mantoux tuberculin skin test
in your facility. Discuss any reliability testing and supervision
procedures that are used at your facility.
- Who will supervise the readings?
- How many readings need to be performed before supervision
is no longer necessary?
|
Last Reviewed: 05/18/2008 Content Source: Division of Tuberculosis Elimination
National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention
|