intradermal tests.pptx

Intradermal tests are done for both diagnostic and therapeutic purposes

1. INTRADERMAL TESTS PRESENTER: Dr Vinayak Akki PGY1 MODERATOR: Dr. A. Venkata Krishna Sir ( Professor & HOD ) PAPER INCHARGE : Dr. A. Venkata Krishna Sir (Professor & HOD) GUIDE: Dr. A. Venkata Krishna Sir (Professor & HOD)

2. OVERVIEW Definition Procedure Interpretation IDT for infectious diseases Bacterial diseases Fungal diseases Parasitic diseases IDT for non infectious diseases

3. DEFINITION A test for immunity or hypersensitivity made by injecting a minute amount of diluted antigen into the skin Also called as Intracutaneous test For the first time used in 1916

4. Intradermal tests are widely used to support the diagnosis of dermatological and nondermatological diseases. They are mainly indicated for the detection of immediate (Type I hypersensitivity) and delayed type hypersensitivity (DTH, Type IV hypersensitivity) towards exogenous or endogenous antigens.

5. Prerequisites Before undertaking intradermal test, it is advisable to stop or avoid systemic steroids or immunosuppressive agents at least three days before the procedure as moderate to large doses of corticosteroids may inhibit a DTH reaction.

6. Intradermal testing is in general safe with few reactions and does not appear to result in sensitizati on , resuscitative measures should be kept ready as there remains possibility of anaphylaxis. In case of anaphylaxis supplies needed: Epinephrine 1:1000 Systemic corticosteroid Systemic antihistamine Oxygen

7. Contraindications Severe eczem a,dermographism Severe asthma. Drug intake such as antihistamines, ACE inhibitors,beta blockers,antidepressants,calcineurin inhibitors as they affect result interpretation. Acute or chronic UV B radiation exposure in the skin test area. Pregnancy

8. Side effects: Irritation Itching Anaphylaxis Granuloma formation in TST Exacerbation of asthma

9. PROCEDURE The uniform feature of all intradermal tests is the injection of the antigen into the superficial layer of the dermis through a fine-bore (26 or 27-G) needle with its bevel pointing upwards.

10. The quantity injected may vary from 0.01 to 0.1 ml but conventionally 0.1 ml is universally used. Although the tests could be done at any site, the proximal part of the flexor aspect of the forearm is conventionally used. This site can be conveniently exposed and the skin of the proximal area is more sensitive.

11. INTERPRETATION OF INTRADERMAL TESTS The optimal time for reading the reaction depends upon the pharmacological agent used for the test and the type of immunological reaction to be observed. IDT for drug sensitivity are read at 15 minutes. IDT for the detection of DTH are read at 48h, although they can be read as early as 12h and as late as 4 days. The size of the induration is more important than erythema while interpreting Type IV hypersensitivity.

12. The measurement of a wheal is made by diameter, more sophisticated methods like volume measurements and Doppler flow have been used. If the wheal is not circular, an approximation may be made by averaging maximum/minimum diameters, or more accurately the area may be calculated by the formula D 1* D 2 * π/4, where D 1 and D 2 are the maximum and minimum diameters . For irregular wheal's, a tracing may be made on squared paper. Pseudopodia should be noted, but for measurement of diameter they are ignored. Attempts to assess the volume of a wheal are less satisfactory for routine use

13. The size of the wheal is not directly proportional to the dose of the active agent, but may vary with the total volume of fluid injected. For accurate quantitative observations, wheal diameters below 4 mm or above 15 mm cannot be relied upon.

14. INTRADERMAL TESTS ARE BROADLY DIVIDED INTO TWO CATEGORIES INTRADERMAL TESTS USED FOR INFECTIOUS DISEASES. INTRADERMAL TESTS USED FOR NON-INFECTIOUS DISEASES.

15. INTRADERMAL TESTS USED FOR INFECTIOUS DISEASES IDT USED FOR BACTERIAL INFECTIONS Tuberculin test Lepromin test Frei's test Ito Reenstierna test Anthraxin test Foshay test Dick's test IDT FOR FUNGAL INFECTIONS Trichophytin test Candidin test Coccidioidin test Histoplasmin test IDT FOR PARASITIC INFECTIONS Leishmanin test Casoni test Onchocerca skin test

16. INTRADERMAL TESTS USED FOR NON INFECTIOUS DISEASES Intradermal sensitivity test for common allergens Predictive sensitization tests Autologous serum skin testing (ASST) Kveim-Siltzbach test Pathergy test Auto erythrocyte sensitization test Histamine test Pilocarpine test

17. INTRADERMAL TESTS USED FOR INFECTIOUS DISEASES

18. IDT USED FOR BACTERIAL INFECTIONS Tuberculin test Also known as Pirquet's test/reaction or scarification test. Antigen used - Tuberculin, a purified protein extract of bacilli grown on 5% glycerol broth (ultra filtrate of tubercle bacilli containing over 200 ag shared with bovine BCG and many NTM) Routinely used is PPD equivalent to 1 TU of RT23 strain with tween 80. PROCEDURE: 0.1ml is injected intradermally on the flexor aspect of the forearm and a reading taken after 48h-72h (Mantoux method). RESULT: Induration measuring more than 10 mm in diameter is considered to be a positive response while that measuring less than 5 mm is considered as negative.

19. A positive test indicates past or present infection with M. tuberculosis (latent or clinical) or vaccination with bacillus Calmette-Guerin (BCG) or other mycobacteria. A tuberculin test represents DTH but this response is not associated with protective immunity against M.tuberculosis. A positive test does not indicate active infection except in children younger than two years and is directly proportional to the strength of the reaction. An induration of more than 15 mm is usually not due to BCG vaccination. Readings between 6 mm and 9 mm are doubtful and could be because of an atypical mycobacterial infection.

20. 5 mm considered + for high risk group which includes – close contacts, radiographic abnormalities, HIV, on corticosteroids, on immunosuppressive drugs. 10 mm considered + for migrants in endemic areas, health care workers, homeless, silicosis, DM, CKD 15 mm considered + for no risk persons

21. A negative tuberculin test can also occur due to technical errors. A negative tuberculin test indicates non-exposure or decreased or absent delayed hypersensitivity to M. tuberculosis as in HIV infection/AIDS, disseminated tuberculosis, primary immunodeficiency disorders of CMI, lymphoreticular malignancies, sarcoidosis, etc. A repeat test is not advocated before one week as the tuberculin injected for the first test has a booster effect on the subsequent dose.

22. Small non necrotising response is consistent with protection. Strong reaction to tuberculin directly correlates with prevalence of active Tb. Weaker reaction does not correlate with the active Tb and may be due to other infection or waning of reactivity due to ageing (reversion).

23. TST can act as a triggering factor for granuloma annulare TST is recommended in the work up of patients with sarcoidosis TST is routinely recommended before starting steroids, immunosuppressive, immunomodulator drugs and biologicals

24. Tuberculin's from atypical mycobacteria or environmental bacteria have also been prepared. They include PPD-B for Battey mycobacteria, PPD-Y for M. kansasii , SCROFULIN for M scrofulaceum and BURULI for M. ulcerans . Lack of specificity is the major drawback in population vaccinated with BCG Now TST is being replaced by IGRA (interferon gamma release assay) & NAAC ( nucleic acid amplification)

25. Disease Reactivity Primary inoculation Tb At beginning, + later Scrofuloderma + Orificial tb Usually + Ac cutaneous tb - Metastatic tuberculous abscess Usually + but can be – due to poor GC Lupus vulgaris Strongly + Tuberculids Strongly + but bx & culture - Lichen scrofulosum Strongly + and can even ulcerate Papulonecrotic tuberculid + and necrotic r/n Erythema induration of bazin + Lupus miliaris disseminated faciei + Tuberculous mastitis +

26. Lepromin test It is a prognostic test which helps in classifying leprosy. It cannot be used for diagnostic purpose since it is positive in a significant number of normal people and is negative towards the lepromatous pole of the disease. Antigens used – 1. Mitsuda lepromin , an autoclaved suspension of tissue (whole bacilli) obtained from experimentally infected armadillos (Lepromin A) 2. Dharmendra lepromin , a purified chloroform-ether extracted suspension of M. leprae (fractionated bacilli with soluble protein component). More specific . In India, lepromin antigen is prepared by the Central Leprosy Teaching and Research Institute, Chengalpattu,Tamil Nadu.

27. Result: The response after intradermal injection is biphasic, with an early Fernandez reaction (48-72 hours – erythema with induration) and a late Mitsuda reaction( 4 weeks – nodule/ulceration). Both responses are manifestations of CMI towards the antigen.

28. Response Time Reading Inference Remarks Fernandez reaction 48-72h Erythema or induration <5 mm Erythema or induration 5-10mm Erythema or induration 11-15mm Erythema or induration >16mm Negative Weakly positive(+) Moderately positive(++) Strongly positive (+++) More prominent with Dharmendra Lepromin Measure of existing DTH Mitsuda reaction 3-4 weeks Nothing to see/feel Papule<3mm Erythematous papule 4-7 mm Erythematous papule 7-10 mm Erythematous papule >10 mm or One of any size with ulceration. Negative Doubtful Positive (+) Positive (++) Positive (+++) More prominent with mistuda Lepromin indicates the ability to generate a cell mediated immune response

29. In immune competent person early lepromin reaction indicates a state of sensitisation against M leprae & was regarded as evidence for prior infection Late reaction represents CMI in patients & normal persons Incidence of LL is higher in sub clinically infected & Mitsuda negative persons Test is positive in TT & BT with increase in sensitivity in T1R & negative in other types.

30. Provides immunological aid in classification Spectrum TT BT BB BL LL Reactivity +++ +/++ -/+WEAKLY - VE -VE NEGATIVE in histoid leprosy Strongly POSITIVE in HIV + leprosy

31. Limitations : Low specificity Paucity of human leproma Reduced availability of test subjects

32. MEDINA TEST : Similar to lepromin test but antigen is prepared from lesions of lucio leprosy Second generation based tests – soluble antigen lipoarabinomannan (MLSA-LAM) MLCW antigen to test cell proliferation & CMI

33. Frei's test Frei's test was developed in 1925 for lymphogranuloma venereum (LGV) Antigen used - Frei's antigen. It indicates delayed hypersensitivity to an intradermal standardized antigen prepared from chlamydia grown in the yolk sac of a chick embryo. Result: The test is read after 48h and again on the fourth day. A nodule more than 5mm at fourth day is considered a positive response.

34. A positive test indicates past or present chlamydial infection. Frei's test becomes positive two to eight weeks after infection. Frei's antigen is common to all chlamydial species and is not specific to LGV. Due to its non specific nature, the test is no longer used.

35. Ito Reenstierna test Also known as Ducrey's test. This test was detects hypersensitivity against Hemophilus ducreyi (chancroid). A response indicates cell-mediated hypersensitivity against H. ducreyi and is due to past or current infection with the organism. The antigen is not commercially available.

36. Anthraxin test The anthraxin skin test measures DTH to anthrax antigens is used as a diagnostic tool. It has also been recommended by the WHO for evaluation of immunological memory against anthrax. Antigen used - Anthraxin, a cell wall extract from the vegetative, non capsulated strain of B. anthracis (Sterne strain), consists mainly of a complex of peptidoglycans and polysaccharides.

37. Anthraxin is prepared by using a cell wall extract in place of the vaccine antigen. The anthraxin skin test can differentiate between exposed and unexposed individuals, even if they have been immunized. Result: The anthraxin skin test becomes positive in most of the cases (80%) in the first three days of the disease, and stays positive for a long time after recovery from the disease. Anthraxin skin test is a valuable method for early diagnosis of acute anthrax and is the only method for the retrospective diagnosis of human anthrax.

38. Foshay test The test involves intradermal injection of a suspension of killed Bartonella henselae , the causative agent of cat-scratch disease. Antigen used - The antigen is prepared from the sterile lymph node material obtained from a patient of cat-scratch disease. Result: The appearance of an area of erythema more than 5 mm diameter after 48h at the injection site is considered a positive reaction. A positive test is a sign of past or present infection. The test is of historical importance only, no longer used for diagnosis because of concerns about the transmission of the organism.

39. Dick's test This test was used to identify children susceptible to scarlet fever, but is of historical value as scarlet fever is no longer a common or serious disease. The antigen used is pyrogenic exotoxin or Dick's or scarlatinal toxin of Streptococcus pyogenes . It is also known as erythrogenic toxin because intradermal injection causes an erythematous reaction in a susceptible person. Procedure: About 0.1 cc of the toxin in the dilution of 1:1000 is injected intradermally on the forearm.

40. Result: the response is read after 24h. The reaction is considered positive when there is an erythema more than 5 mm in diameter and strongly positive if induration also develops. A positive reaction develops after 8-12h and reaches its maximum after 24h. It is negative in convalescent patients and in insusceptible individuals.

41. IDT FOR FUNGAL INFECTIONS Trichophytin test This test is performed to detect allergic hypersensitivity towards dermatophytes. Antigen used - Trichophytin antigen is a glycopeptide extracted (using acetone-ethylene glycol extraction method) from the spores and mycelia of dermatophytes, mostly Trichophyton mentagrophytes. Procedure: Trichophytin in the concentration of either 10 μg, 1 μg or 0.1 μg in 0.1 ml of normal saline is injected intradermally into the flexor forearm.

42. Result: The test is read after 20 min for an immediate reaction and after 24 or 72h for a delayed response. Erythema, edema or induration may be seen and a papulovesicular or ulcerative lesion can also occur. A wheal larger than 10 mm in diameter at 20 min and induration more than 5 mm at 72h is considered a positive response.

43. Candidin test Hypersensitivity towards Candida albicans is universal. Hence, a test cannot be used to diagnose the infection. The candidin test serves as an aid to evaluate the cellular immune response in patients suspected of having reduced CMI. Antigen used - Candidin is used as a recall antigen for detecting DTH by intradermal testing. Candidin is made from the culture filtrate and cells of two strains of Candida albicans . Compared with healthy controls, reactivity to candidin is significantly reduced in patients with AIDS, Hodgkin's disease and sarcoidosis(tuberculin sensitivity is more reliable in the latter case).

44. Procedure: The test dose of 0.1 mL is injected intradermally on the forearm Result: an induration response in excess of 5 mm at 48h after injection in immunocompetent persons with cellular hypersensitivity to the antigen.

45. Coccidioidin test Antigens used - two antigens available: coccidioidin and spherulin. Coccidioidin is prepared from autolysates of the mycelial phase (saprophytic phase) of Coccidioides immitis , and spherulin, a more sensitive reagent, from the spherule phase (parasitic phase). A positive test is helpful in detecting exposure to the fungus Coccidioides immitis . It can help in differentiating the chronic pulmonary disease caused by this fungus from other chronic cavitary, nodular and fibrotic diseases like tuberculosis and malignancies. The test is negative in patients with disseminated disease or in patients with thin-walled cavities.

46. Histoplasmin test Histoplasmin skin testing is useful in epidemiological studies , such as investigations of case cluster or the definition of endemic areas but is not predictive of histoplasmosis. An antigen containing the M and H precipitins of Histoplasma capsulatum tends to elicit both immediate and delayed hypersensitivity, and hence more false-positive reactions. An antigen that is deficient in the M component can reduce this problem.

47. IDT FOR PARASITIC INFECTIONS Leishmanin test ( Montenegro test) Antigen used - Leishmanin, which contains killed Leishmania. A positive reaction consists of a palpable nodule more than 5 mm in diameter developing in 48 to 72h and indicates DTH, but not necessarily immunity, to leishmania organisms. The test is not species-specific. It becomes positive early in the course of cutaneous or mucocutaneous leishmaniasis (except in diffuse cutaneous leishmaniasis) and only after recovery from visceral leishmaniasis. It is highly sensitive for cutaneous leishmaniasis.

48. It is a useful and important tool for epidemiological, immunological, and diagnostic studies and is an essential component of vaccine trials. However, it cannot distinguish between present and past infection.

49. Casoni test: Done for Hadatid disease or Echinococcosis. Intradermal injection of 0.2 mL of fresh sterile hydatid fluid or hydatid antigen produces in half an hour a 5 cm wheal with multiple pseudopodia fading in an hour in positive cases. Normal saline is used as a control. A rapid slide test has been proposed for resource poor settings.

50. Onchocerca skin test The intradermal test with products from Onchocerca volvulus is highly sensitive in the detection of active onchocerciasis. However, a few reports indicate decreased CMI to parasite-derived antigens, delayed skin-test reactivity, and response to unrelated antigens during Onchocerca volvulus infection. Intradermal tests in various skin or systemic infections thus serve an important role in reaching a diagnosis and predicting the prognosis of these conditions.

51. INTRADERMAL TESTS USED FOR NON INFECTIOUS DISEASES

52. Intradermal sensitivity test for drug Intradermal testing is a rapid, convenient and reproducible method of detecting drug hypersensitivity (drug-specific IgE antibodies). It is commonly performed for penicillin, general and local anaesthetic agents, tetanus toxoid, iodinated radiocontrast media, insulin, heterologous sera, collagen chymopapain etc. Intradermal testing is in general safe with few reactions and does not appear to result in sensitization. However, resuscitative measures should be kept ready as there remains possibility of anaphylaxis.

53. Penicillin intradermal skin tests should be carried out using major determinant (benzyl penicilloyl polylysine, PPL)and minor determinant mixture (benzyl penicillin, benzyl penicilloate and benzyl penilloate) antigens. The test can also be performed using 2-10 units of freshly prepared penicillin. Skin test is read at 20 minutes.

54. Result: Negative response no increase in size of original bleb and no greater reaction than the control site Ambiguous response wheal only slightly larger than initial injection bleb, with or without accompanying erythematous flare and slightly larger than the control site; OR discordance between duplicates Positive response itching and significant increase in size of original blebs to at least 5mm. Wheal may exceed 20 mm in diameter and exhibit pseudopods

55. Negative intradermal test does not rule out penicillin sensitivity. Other agents are tested similarly for detection of immediate and delayed type of hypersensitivity. Intradermal skin tests have no predictive value in non IgE-mediated reactions such as serum sickness, haemolytic anaemia, drug fever, interstitial nephritis, contact dermatitis, maculopapular exanthemata or exfoliative dermatitis. Skin testing is contraindicated where there is a history of exfoliative dermatitis, Stevens-Johnson syndrome or TEN.

56. Predictive sensitization tests Sensitization index is the relative capacity of a given agent to induce sensitization in a group of humans or animals. Predictive sensitization tests are used to compare the sensitizing properties of new products or chemicals with those of known substances. Both in guinea-pigs and humans, an estimate of the sensitizing potential can be performed using intradermal route. Draize test and Freund's complete adjuvant test are intradermal methods of testing sensitization potential.

57. Autologus serum skin testing (ASST) Autologous serum skin test is a simple in-vivo clinical test for the detection of basophil histamine releasing activity and to diagnose chronic autoimmune urticaria among chronic spontaneous urticaria patients. About 25-45% of patients of chronic idiopathic urticaria have autoantibodies against the high affinity IgE receptor FceRI or IgE that are capable of histamine release. These antibodies, if present in serum, can cause wheal and erythema following intradermal serum injection. This reaction forms the basis of the ASST. Procedure: The test is performed by injecting 0.05 ml of the patient's own serum intradermally into the left flexor forearm two inches below the antecubital crease and a saline control into the right forearm.

58. Serum is obtained after withdrawing 5 ml of venous blood and standing for about 45 min for separation. The process can be hastened up by centrifugation of the blood. About 5 ml of venous blood was collected in a sterile vacutainer and allowed to clot at room temperature for 30 min. Serum was centrifuged at 2000 rpm for 15 min and 0.05 ml of autologous serum was injected intradermally, in uninvolved skin, using a 1 ml insulin syringe (30 gauge needle) into the right forearm 2 cm below the cubital fossa. Similarly, 0.05 ml of 0.9% sterile normal saline (negative control) was injected intradermally proximally into the left forearm, and at a distance of at least 5 cm, 0.05 ml of histamine (10 μg/ml) was injected distally into the left forearm as a positive control.

59. A serum induced erythematous wheal with a diameter of 1.5 mm more than the saline induced response within 30 min was taken as positive

60. ASST positivity has been found to correlate well with the severity and duration of attack of urticaria. The cases of idiopathic urticaria which are ASST positive are designated as autoimmune urticaria. Western blot, ELISA, flow cytometry may be useful for screening in the future

61. Intradermal allergy testing A small amount of diluted allergen is injected into the dermis. It is carried out with allergen concentrations 100 to 1000 times less than that used for skin prick tests. It increases the sensitivity but decreases the specificity of the test. It is most commonly used in testing for drug and venom allergy. IDSTs have a very high non-specific reaction rate and are not recommended for testing with inhalants or foods and food allergens. Moreover, intradermal tests carry a higher risk of adverse reactions than SPTs.

62. Kveim-Siltzbach test It is a valuable intradermal test for the diagnosis of sarcoidosis. The test can be utilized to differentiate from other causes of diffuse pulmonary mottling, uveitis and erythema nodosum. The antigen is prepared from the splenic tissue obtained from a proven case of sarcoidosis either after splenectomy or during autopsy. About 0.1-0.15 ml of this antigen is injected intradermally, a nodule develops after four to six weeks, which can be biopsied for histopathological confirmation of the diagnosis.

63. False positive reactions were found in an appreciable proportion of patients with Crohn's disease, ulcerative colitis and tuberculous lymphadenitis, but only with few batches of commercially available antigens.

64. Pathergy test Pathergy is the development of a papulopustular lesion around a puncture site on the skin, 24-48h after the injection of a sterile substance like normal saline intradermally. This phenomenon forms the basis of the pathergy test. The test is used as a diagnostic criterion for Behcet’s disease. Results of the test depend upon the type of needle used; reactivity varies with the diameter and sharpness of needle. The sensitivity and intensity of the reaction is considerably less with sharp needles and needles with smaller diameter.

65. Pathergy is also a reported phenomenon in pyoderma gangrenosum, in hairy cell leukaemia, Hodgkin's lymphoma and in chronic myeloid leukaemia treated with interferon alpha. Histopathological evaluation of the test is not found to be more sensitive than the clinical evaluation.

66. Auto erythrocyte sensitization test The intradermal test for the diagnosis of auto erythrocyte sensitization syndrome is done with washed RBCs of the patient in the intrascapular region with a saline control on the opposite side. Patient develops a painful ecchymotic reaction within two hours at the site of the injection indicating positive test. The control site does not show reaction.

67. Histamine test When histamine is injected intradermally, it causes bright red histamine flare due to capillary vasodilatation. However, this effect is due to axon reflex within dermal nerves. The histamine test can be used to test integrity of dermal nerves in cases of tuberculoid leprosy. One drop of histamine acid diphosphate 1 in 1000 (1mg/ml) is placed on the skin surface, one each on the normal skin and the other on the suspected patch. Superficial prick is made through the drop. The histamine solution is wiped off and the area is watched for 5 minutes. Response takes little longer on the extremities.

68. In the normal skin, a wheal at the site of prick and a flare of 2 cm diameter surrounding the wheal would be seen (test labeled as positive). The flare disappears in 10 minutes. In the patch of leprosy the flare is impaired or absent and only a wheal is seen (test negative). The flare is feeble and delayed in indeterminate and borderline leprosy, and absent in a tuberculoid lesion.

69. The response in the skin to histamine depends on the integrity of nerves of the autonomic nervous system. A utonomic nerves are nonmyelinated nerve fibers sheathed only by Schwann cells and are distributed along with the small dermal blood vessels. In early leprosy, which manifests as localized skin patches, the Schwann cells are parasitized by M. leprae . There is perivascular and perineural inflammation and the functions of sympathetic nerves of the skin supplying the blood vessels are impaired, even before the sensory nerves are affected.

70. The test is useful only to differentiate hypopigmented macules of leprosy from those of other skin diseases. There will be a normal flare (positive test) in other hypopigmented macules due to non leprosy conditions like vitiligo, pityriasis alba, fungal infections, etc. T he histamine test will also be negative in patients without any skin changes but only with areas of nerve deficit due to other peripheral neuropathies. I n patients with dark skin this test may not be useful because the flare is not easily visible.

71. Pilocarpine test Pilocarpine intradermal test is used to detect the integrity of dermal nerves in suspected cases of tuberculoid leprosy. About 0.2 ml of 1 in 1000 solution of pilocarpine nitrate is injected intradermally into the lesion, the injection site is then painted with tincture of iodine and then dusted with starch powder. Sweating, if present, causes blue discoloration of the powder. Alternatively, quinizarin powder can be used in place of starch powder with the advantage that there is no need for painting the test site with tincture of iodine.

72. Prausnitz - Kustner (PK) Test Used to test people for life threatening allergens such as bee venom Test involves transferring serum from the test subject to another healthy person. Serum from allergic patient is injected into healthy person and 24 hrs later suspected antigen is injected intradermally into healthy person. If allergic patient had developed antibodies, this will cause local reaction in the healthy person when the antibodies mix with antigen A positive PK test appears as wheal and flare demonstrating type 1 hypersensitivity reaction reaction. No longer recommended now.

73. Therapeutic uses of IDT: Autoinoculation : Done in viral warts, by excising ,mincing and implanting homogeneous tissue in a small dermal pocket in forearm. Antibodies thus produced help in clearing the warts It’s an effective treatment modality for multiple and recurrent warts.

74. Autologous serum therapy: Used in Chronic urticaria. Repeated injections of autologous whole blood or serum can induce desensitisation or tolerisation of auto reactive chronic urticaria patients to pro inflammatory signals expressed in their circulation.

75. REFERENCES Rook’s textbook of dermatology IAL textbook of leprosy IADVL textbook of dermatology IJDVL Internet