skin prick test

1. MANTOUX
DR. FIROZA HAKKIM
PG- 1STYR CHEST MEDICINE

2. TUBERCULIN SKIN TEST
 Detect infection with tubercle bacilli
 Low technology
 In expensive
 Easy to administer, read

3.  Based on – infection with mycobacterium
tuberculosis produces sensitivity to certain
components called sensitins, which are
contained in culture extracts called tuberculins

4.  Used among children for detection of
tuberculosis infection and as a supportive tool
for diagnosis of tb disease
 Limited role in diagnosis of tb among adults
living in areas where tb is highly endemic
 Used by epidemiologists for assesment of tb
situation in community

5. History

6.  Sir robert koch – produces a filtrate prepared
from heat sterilized concentrated broth cultures
of human tubercle bacilli
Initialy prepared for treatment of
Tb , but proved ineffective .
Subcutaneous inoculation in a patient suffering
from tb resulted in local reaction at inoculation
site laid foundation of its use as diagnostic aid
Was namedOLDTUBERCULIN (OT)

7. Clement von pirquet
in 1907 , observed
that
Tiny scratch with a
little quantity of
tuberculin resulted in
a local reaction at the
test site

8.  Moro in 1908 announced the patch test
 Tuberculin was incorporated into an ointment
that was smeared onto skin , with a piece of
guaze over it

9. Charles mantoux
developed the
intradermal test, to be
administered by
injection as a measured
volume ( mantoux test )

10.  Other test – HEAF test – used a simple
instrument that caused six spring loaded
needles to pierce the skin with a drop of
undilutedOT

11.  TINE test – disposable multi puncture test
where tuberculin was introduced into skin by
puncture with four tines coated with dried
tuberculin

12.  ONL
Y MANTOUXTECHNIQUEWHICH
ALLOWEDQUANTITATIVE MEASUREMENT
HASSTOODTHETESTOFTIME,AND IS NOW
THE STANDARD METHOD OF
ADMINISTRATIONOFTUBERCULINSKINTEST

13. Florence B.
Seibert

14.  Siebert in 1934 showed that active principle in
tuberculin reaction was the protein fraction
 Made a preparation from heat concentrated
synthetic medium OT by precipitation with
trichloroacetic acid .
 It still contained lipopolysaccharides and
nucleic acid
 Later precipitation achieved by ammonium
sulphate to obtain a preparation with less
nucleic acid and polysaccharide content
termed PURIFIED PROTEIN DERIVATIVE
(PPD)

15.  ONETUBERCULINUNIT [TU]OF PPDWAS
DEFINEDASTHEACTIVITYCONTAINED IN
0.02 MICROGRAMOF PPD

16. •Statens serum institute , copenhagen
produced a large batch of PPD in 1952 at
behest of unicef andWHO, and was
designated RT23
•TWEEN 80 is added to prevent
reabsorption of tuberculin to glass surface
•Seed lot of PPD RT23 is maintained by
BCGVACCINE LABORATORY ,GUINDY ,
CHENNAI.
•It is reconstituted and is supplied as ready
to use preparation in isotonic buffer
solution as 5ml vials, 0.1 ml corresponding
to 1TU.

17. Immunological basis
 Individuals infected with mycobacteium
tuberculosis respond with delayed type
hypersensitivity

18. Test site
Injection
of
tuberculin
Proliferation
of sensitized
T cell
lymphocytes
Cytokines &
chemokines
released
Lymphocytes
& monocytes
attracted
Increased
permeability
of local blood
capillaries
INDURATION at
test site

19. Skin changes in TST
 Reaction include a delayed course reaching a
peak more than 24 hrs after injection and an
induration with occasional vesicilation and
necrosis
Delayed type hypersensitivity reaction peaks by
48 to 96 hours, with an area of erythmatous
induration

20. Standard tuberculin skin
test
 Standard test employs a single batch
tuberculin ie PPD RT – 23
 Dose – 0.02 microgram [ 1TU ] of PPD RT -23
in 0.1 ml of the diluent withTween 80

21.  2TU of PPD RT – 23 is now recomended as
the standard dose , based on a series of
studies conducted in india
 It demonstrated equal sensitivity for 1TU &
2TU in detecting true infection with
mycobacterium tuberculosis.
 Available in 1TU/0.1ml, 2TU/0.1ml, 5TU/0.1ml
and 10TU/0.1ml strengths.

22. 1TU/0.1ml
5TU/0.1ml

23.  Earlier special glass syringes with a platinum
needle was preferred for injection.
 These days disposable tuberculin syringes
(1ml) are preferred.

24. Glass syringe 1 ml Plastic syringe

25. Storage
 Tuberculin vials – stored at 2-8 °C and used
before expiry period
 Avoid exposure to sunlight and heat
 Never freeze or keep at temp exceeding 20°C
 Vial once used may be re- used within a
maximum of 48 hrs

26. Administration
 Administerd 2-4 inches
below the elbow joint
 Place the forearm palm
side up on a firm well lit
surface
 Select an area free of
barriers ( scars, sores ) to
placing and reading
 Clean the area with an
alcohol swab

27.  Check expiry date on
vial and ensure vial
contains tuberculin
(5TU per 0.1ml)
 Use a single dose
tuberculin syringe with
a ¼ to ½ inch 27 gauge
needle with a short
bevel
 Fill the syringe with 0.1
ml of tuberculin

28.  Insert slowly , bevel up
at 5- 15 degree angle
 After injection a tense
pale wheal should
appear over the needle
 Check the skin test-
wheal should be 6-10
mm in diameter . If not
repeat test at a site at
least 2 inches away from
original site
 Record information (
date, time of
administration, injection
site, location, lot
number of tuberculin)

31.  Educate the patient on the possible
reactions to theTST (e.g., mild itching,
swelling, irritation).
 Instruct patient not to rub, scratch or put
an adhesive bandage or lotion on the test
site.
 Schedule reading date and explain the
importance of the patient returning for
reading in 48 to 72 hours.

32. Reading (48-96 hrs)
 Visually inspect site under good
light.
 Use fingertips to find margins of
induration
 Mark induration by using fingertips
as a guide for marking widest
edges of induration across forearm
 Measure the induration ( not the
erythema) . Place the 0 ruler line
inside left dot edge. Read ruler
line inside right dot edge
 Record measurement of induration
in mm
 Do not record as positive or
negative
 Records made of bullae, vesicles,
ulceration etc at test site

35. Interpretation
• Signifies reaction with tubercle
bacilli, irrespective of BCG
vaccination status
Size of induration
15 mm & above
• Cross sensitivity induced by environmental
mycobacteria
• BCG induced sensitivity
• Infection with mycobacterium tuberculosis
Size of induration
10-14 mm
• Cross sensitivity by environmental
mycobacteria/ BCG vaccination/ infection
with tubercle bacilli in the presence of
immunosuppresive conditions
Size of induration
5-9 mm
• Indicates absence of any type of
mycobacterial infection except in
individuals with severe degree of
immunosuppression
Size of induration
less than 5 mm

36. Adverse effects
 Some atopic individuals, develop an urticarial
wheal, which may dissapear within minutes.
 Occurence of such an allergic reaction does
not signify the presence of TB.
 Systemic allergic reactions seldom occur
 Formation of vesicles, bullae, lymphangitis,
ulceration or necrosis in a proportion of
children indicates high degree of tuberculin
sensitivity.

39. Skin sensitivity to tuberculin
 Persons with sensitivity to tuberculin are
called ‘Reactors’.
 Not all reactors are infected with tubercle
bacilli.
 Sensitivity to tuberculin may oocur due to
infection with environmental
mycobacteria
BCGVaccination
Infection with Mycobacterium
tuberculosis

40. Infection with environmental
mycobacteria
 Sensitivity induced by them cross-reacts with
tuberculin and is known as ‘NonSpecific
Sensitivity’ (NSS).
 sensitivity induced by these results in smaller
reactions.
 Distinction from true infection is not always
very clear.
 Highly prevalent in most parts of India.

41. BCG Vaccination
 Sensitivity may vary from very weak to about
the same level as natural infection.
 Depends on strength of vaccine used,
handling, administration, and time interval
between vaccination and testing.
 Generally peaks at 10 weeks then begin to
wane.
 UnderUIP in India, a reduced dose of 0.05 ml
of Danish 1331 strain is administered.

42.  About 70% of children upto 9 yrs of age with
a BCG scar elicited either no rection or
<10mm to 1TU PPD withTween 80.
 It may be inferred that the BCG induced
sensitivity is generally weaker than that of
infection with tubercle bacilli.
 Weak sensitivity does not imply that
vaccination is ineffective.

43. Infection with Mycobacterium
tuberculosis
 Most individuals harbouringTB infection
usually elicit a larger reaction to tuberculin
 The probability of true positives increases as
the reaction size increases
 Probability is also increased in the presence
of history of contact with a sputum smear
positive case ofTB.

44. False positive reactions
 Infection with environmental mycobacteria.
 BCG vaccination.
 Repeat testing.
 Testing with high dose of tuberculin.
 Reading errors.
 Needle injury.

45. False negative reactions
 Non significant reaction does not always
exclude the presence ofTB infection or
disease.
 Most common reasons being :
 Improper storage
 Poor technique
 Other reasons :
 Immunosupression
 DisseminatedTB
 Undernutrition

46.  Hodgkin’s
 Malignancy
 Sarcoidosis
 HIV –AIDS
 Vaccination with live virus vaccines
 Acute viral infections
 Window period
 Infants < 3months ( immature immune system)
 Old age
 Cutaneous anergy
 Supression due to live virus vaccines appears
after 48 hrs of vaccination and start waning 4-6
wks later.

47. Anergy
 Anergy refers to failure to mount a full
immune response against a target.
 Term ‘ANERGY’ was coined byVon Pirquet
 Commonly used antigens for anergy panel
contain trychophyton, candida , etc
 Anergic patients are more likely than
immunologically intact patients to present
with noncavitoryTB.

48.  In sarcoidosis patients, anergy to tuberculin
can be restored by concurrent administration
of hydrocortisone.
 This paradoxical reaction presumably also
occurs inTB patients who have been
desensitized for tuberculin.

49. Reversion, Conversion and
Booster Phenomenon
 Reversion:
 In elderly & many adults, significant
reactions to tuberculin declines with age.
 Estimated to occur at a rate of 5% per yr.
 Attributed to waning of CMI or loss of
lymphocyte blastogenic capacity in elderly.

50. Booster phenomenon
 Boosting of the size of the second test by the
small amount of tuberculin injected for the first
test.
 Results from ‘recall’ of the sensitivity.
 To avoid this, repeat test should be given at a
different site within one week of the first test.
 Boosting effect was observed when test
repeated after 2 months ,not when repeated
after 18 months.

51. Conversion
 Simple tuberculin conversion from a non
significant reaction at first test to a significant
reaction at a subsequent test.
 Larger increase in reaction size (10mm or more)
correlates better with the risk of developingTB.
 Other causes can be boosting effect, infection
with environmental mycobacteria in the
intervening period.
 For detection of new infections, there should be
a significant increase in reaction size (14mm or
more) in the subsequent test, one-and-half to 3
yrs apart.

52. Interpretation in HIV
patients
 All HIV seropositive individuals should be
assessed for activeTB.
 Once activeTB is excluded,TST is done as
soon as possible.
 Reliability ofTST decreases asCD4+T-Cell
count diminishes, espp.To < 200/cmm.
 As the prob. of significant induration indicative
ofTB infection is significantly lower in HIV-
infected persons, a lower cut-off point is
advised.

53.  Irrespective of the test results, patients with
evidence of old healedTB inCXR or past H/O
activeTB and a significant reation toTST may
be considered infected for all practical
purposes.
 TST should never be the sole criteria for
diagnosingTB.

54. Interpretation in
sarcoidosis
 TST in patients with sarcoidosis has a high
specificity but poor sensitivity forTB.
 A –veTST in general poulation is a sensitive
test for sarcoidosis.
 A +veTST in patients suspected of havin
sarcoidosis is a specific test forTB, and is an
absolute indication for a thorough work-up for
TB.

55. Epidemiological use
 Tuberculin surveys are carried out among
young children as the results obtained reflect
relatively recent situation.
 Prevalence andAverageAnnual Risk of
Infection (ARI) are calculated.
 ARI is defined as the avg. prob. of acquiring
newTB infection over the course of one year.
 ARI reflects the overall impact of TB prevalence
in a community and the efficiency of TB control
activities.

56. Newer tuberculins
 Further attempts are being made to develop
newer, more species-specific tuberculins.
 One of the improvisations is to avoid heating
to prevent protein denaturation of PPD.
 Electrophoresis andChromatography.
 T-1327 andT-1456 are under progress.

57. Interferon gamma release
assays ( IGRA)
 In vitro assays that detect the presence of
CMI towards M. tb-specific antigens.
 These include the early secretory antigenic
target-6 (ESAT-6), culture filtrate protein 10
(CFP-10), and theTB7.7 antigens.
 The antigens in IGRAs are absent in most of
NTM as well as in BCG strains.

59.  Available methods :
 Quantiferon-TBGold assay (ELISA based)
 Quantiferon-TBGold INTube assay(ELISA
based)
 T-SPOTTB assay (ELISPOT based)

60. Advantages of IGRA’s
 Higher specificity thenTST.
 Less cross reactivity with BCG vaccination and
NTM infection
 Less inter-reader variations.
 No boosting phenomenon.
 Fewer patient visits.

61. Disadvantages of IGRA’s
 A negative IGRA does not rule out activeTB
or LTBI.
 IGRAs are not able to differentiate LTBI from
activeTB.
 In high-TB incidence countries, there is no
added value in using IGRAs to diagnose LTBI,
as the focus of prevention and control is to
identify and treat active cases.

62.  In presence of immunosuppression, a –ve
IGRA should not preclude further
investigations or treatment if clinical suspicion
is high.
 Technically more demanding.
 Higher cost.

63. Conclusion
 Tuberculin test have stood the test of time and
is still widely used for over a century for
detecting the infection withTB and when used
wisely, has promising results.
 For now, it is probably a good strategy to keep
both IGRA’s andTST on the LTBI diagnostic
menu, and select the appropriate test based on
population, purpose of testing and the
available resources.

64. REFERENCES
 SHARMA
 TOMANS
 INTERNET