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Tzank Test

Cytological examination from the floor of a bulla is used to confirm diagnoses of bullous diseases.

In most bullous eruption the smear will show only inflammatory cells.

In pemphigus numerous acantholytic cells with large nuclei and condensed cytoplasm are found.

Herpes simplex, zoster and varicella lesions: the smear shows large, multi-nucleated and mono-nucleated giant cells and ballooning degeneration of the nuclei. 


Diascopy is a  simple procedure which will sometimes provide useful additional information for diagnosis of certain skin diseases such as in lupus vulgaris that shows distinctive yellowish, reddish brown apple jelly nodules.

A glass slide or a clear plastic tongue depressor is pressed firmly on the lesion. The temporary exclusion of blood clearly reveals the presence and sometimes the probable nature of dermal changes. 

Examination of skin scrapings

This is usually used for the diagnosis of fungal lesions. Scraping is taken of the lesions of the scalp, intertriginous areas, feet or other areas. The skin is cleaned by alcohol swab and left to dry.

Scrape the area with a scalpel or the edge of the slide on a clean slide. Add one drop of 10-20 per cent of KOH or SMS preparation. Hyphae and spores appear as oval bodies and refractile against the background of cells and debris.

Fig. 9. Diascopy

Confirmation is usually by culture of the scrapping on special media such as Sabouraud‘s agar medium. 

Blood picture

Different skin diseases show local or systemic blood changes. Therefore blood picture may be of help to reach a diagnosis and may be indispensable in certain dermatoses. Meanwhile, not every dermatological case is in need of a list of laboratory tests that may be a burden and  might bother the patient leading to loss of confidence in the physician.

Blood picture may show the following in certain skin diseases: 


Neutrophilia may accompany the following skin diseases:

  1. Infections, e.g. erysipelas, carbuncle.

  2. Inflammatory disorders including pustular or inflammatory psoriasis, erythroderma, and pyoderma gangrenosum.

  3. Systemic malignancy (leukemia).

  4. Reaction to systemic steroid therapy.


Eosinophilia is common in the following diseases:

  1. Atopic disorders, especially asthma and eczema.

  2. Allergy to food or drugs.

  3. Parasitic infestations: worms (intestinal or systemic), scabies.

  4. Collagen vascular disease, polyarteritis nodosa, dermatomyositis.

  5. Bullous disorders: dermatitis herpetiformis, pemphigus, and pemphigoid.

  6. Erythema neonatorum.

  7. Malignancy, especially Hodgkin‘s disease and eosinophilic leukemia.


Lymphocytosis may be present in the following diseases:

  1. Viral infections, especially exanthemata and infectious mononucleosis.

  2. Bacterial infections: tuberculosis, syphilis, brucellosis, and typhoid.

Erythrocyte Sedimentation Rate (ESR)

ESR is usually non-specific test. A raised ESR is usually due to an increased aggregation of red cells due to an abnormality of plasma proteins, notably an increase in plasma fibrinogen associated with the acute or chronic phase reaction.

Some causes that raise ESR:

  1. Physiological: pregnancy, menstruation, advancing age.

  2. Infections.

  3. Inflammatory disorders, e.g. vasculitis.

  4. Systemic lupus erythematosus (SLE).

  5. Tissue destruction.

  6. Malignant neoplasms.

  7. Paraproteinaemias.

  8. Polycythaemia.

Serum Protein Estimation: this test is used in certain diseases as systemic lupus, hypoproteinemia. 

Antinuclear Antibody (ANA)

May be present with:

  1. Collagen vascular disease, especially SLE.

  2. Chronic liver diseases.

  3. Hashimoto‘s thyroiditis, thymoma, myasthenia gravis.

  4. Pernicious anemia.

  5. Tuberculosis.

  6. Leprosy.

  7. Diffuse pulmonary fibrosis.

  8. Lymphoma or other malignancy.

  9. Ulcerative colitis.



These tests are indicated in certain diseases such as syphilis and non-venereal treponemas mainly Pinta and Bejel. 

Liver function tests

Diseases of liver may manifest with internal and cutaneous manifestations.

Hormonal essay: is an important line in investigating certain skin diseases especially those associated with endocrine dysfunction. 

Cryoglobulins tests

This test shows precipitation of proteins when cooled which redisolves again when heated.
Cryoglobulins are not present in normal individuals.
Skin diseases that show positive test:
Cold sensitivity cyanosis
Raynaud‘s disease
Lupus erythematosus
Lymphgranuloma venerum
Leg ulcers
Cutis marmorata. 


In a warm 10 ml. syringe, venous blood is collected and the serum is separated at 37*C, then cooled in a refrigerator to 5*C. A gelatinous precipitate forms that  redisolves when rewarmed. 

Porphobilinogen Urine Test

This test is specific for acute intermittent porphyria. It is simple and
valuable in screening patients suspected for porphyria.


5 ml of freshly voided urine is mixed with 5 ml of Ehrlich‘s reagent and mixed with 10 ml aqueous saturated sodium acetate. The solution is then extracted with equal volume of chloroform. Porphobilinogen and urobilinogen form a red aldehyde compound with Ehrlich‘s reagent. 

Skin biopsy

Skin biopsy is an important procedure to confirm an accurate diagnosis for a suspected skin lesion.

Skin Tests

Skin tests are introduced into the skin by a variety of techniques to study pharmacological and immunological reactions under controlled conditions. Such tests are extremely valuable, but details of the type of test and the time at which it is read must correspond to the pathological process under consideration.
Interpretation of the relevance of tests, either positive or negative, must always be correlated with the clinical picture.
Severe systemic reactions may occur after the use of standard testing solutions, therefore anti-shock measures as oxygen, adrenaline and hydrocortisone injections should always be at hand when skin tests are performed.


Intradermal tests are much more sensitive than percutaneous methods (the tested allergen is 10- to 100-fold more diluted), but they have a lower specificity. Intradermal testing is usually reserved for venom and penicillin allergy testing when percutaneous tests are negative but there is high clinical suspicion of allergy.

Stinging-Insect Hypersensitivity. Adults who present with a history of a systemic reaction to insects (e.g., bee, yellow jacket, hornet, wasp, fire ant) should be evaluated with allergy skin tests. Children who present with only dermatologic manifestations of a systemic reaction are not at substantially increased risk for future anaphylaxis and do not need allergy skin tests. Management of sensitive patients may include education, avoidance measures, self-administered epinephrine, and allergen immunotherapy.

Drug Allergy. Reliable allergy tests for drugs are available only for penicillin and local anesthetics. In many patients with a history of penicillin allergy, the simplest course is to prescribe an antimicrobial agent that does not contain a beta-lactam ring. In patients with a history of penicillin allergy who have a strong indication for use of a beta-lactam antibiotic, penicillin skin tests can be helpful.

These results suggest that penicillin can be given safely to patients with negative intradermal skin tests to penicillin. Patients with positive penicillin skin tests may be at increased risk for drug reaction, but the specificity of intradermal testing is low.

Percutaneous testing

Several types of skin testing instruments are available for percutaneous skin testing. Each brand of instrument has its own sensitivities and specificities. Positive-control skin tests (histamine) and negative-control skin tests (diluent) are essential for correct interpretation of skin test reactions. About 15 minutes after the application of allergen to skin, the test site is examined for a wheal and flare reaction. A positive skin test reaction (typically, a wheal 3 mm greater in diameter than the negative control reaction, accompanied by surrounding erythema) reflects the presence of mast cell­bound IgE specific to the tested allergen.

Allergy to airborne substances (i.e., allergic rhinitis and asthma) is typically evaluated using a panel of percutaneous skin tests for about 40 allergens. A number of the most commonly used allergenic extracts for skin tests are now standardized  . Percutaneous skin testing has been used to test for food allergy; however, it is less reliable for evaluating food allergy than for evaluating reaction to airborne allergens.

The specificity for food allergen tests is generally low, partly because of cross reactions between some food groups (e.g., legumes). Negative reactions to suggested food allergens on percutaneous tests make a diagnosis of true food allergy unlikely in most cases; however, the poor specificity of these tests precludes a definitive diagnosis of food allergy based on positive test results alone. A double-blind food challenge should be considered when more clinical certainty is needed in diagnosing a serious food allergy.

 Positive and negative skin controls are important in establishing reliable results. Antihistamine medications can interfere with skin testing and should be stopped beforehand. Intradermal testing is more sensitive than percutaneous methods but much less specific. Its use is restricted to testing for allergy to insect stings or penicillin. In cases where skin testing is not available or desirable, laboratory assays for IgE antibodies to specific allergens may be used. These assays are generally less sensitive than skin testing methods. 

There are several types of specific allergy tests. 

1- Immediate-type hypersensitivity (IgE) skin tests are typically used to test for airborne allergens, foods, insect stings, and penicillin. Immediate-type hypersensitivity also can be evaluated through serum IgE antibody testing called radioallergosorbent testing (RAST). Immediate-type hypersensitivity skin testing is most commonly used in the diagnosis of allergic rhinitis, allergic asthma, food allergy, penicillin allergy, and stinging-insect hypersensitivity. Skin testing can be performed by the percutaneous route (diluted allergen is pricked or scratched into the skin surface) and by the intradermal route (injection of allergen within the dermal layer).

2- Delayed-type hypersensitivity skin tests (patch-type skin tests) are commonly used in patients with suspected contact dermatitis. Some common allergens for patch testing are rubber, medications, fragrances, vehicles or preservatives, hair dyes, metals, and resins. This review focuses on immediate-type hypersensitivity skin testing and serum IgE antibody testing.


Patch tests are usually used to detect contact sensitizers of the delayed hypersensitivity type. Patch test is easy to apply and more safe than other skin tests.

Patch testing proves only that the patient has a contact sensitivity to a specific contactant, but  this does not necessarily  mean that this substance in the patch test is the only that can cause the reaction but  there may be other substances  that may cause such reaction. 


Precautions should be considered to have correct and safe interpretation.

  • Antihistamines intake: patients using antihistamines especially the long acting or those on systemic steroids .The test should be postponed till the effect of these is minimal which may take few days or weeks. Antihistamines usually have no appreciable effect on delayed hypersensitivity patch tests.

  • Acute eczematous lesions: re-exposure with more antigens in the test may cause more flare-ups of the lesions especially in children and hypersensitive patients.

  • Dilution of the testing substance: The substance applied in the patch test should not be irritant substance and this is why the substance should be diluted and not applied in its full strength as in cosmetics or other sensitizers.

 Different Patch Tests

  1. Open patch test - this test is used in testing the plant oleoresins.


    Acetone extracts of the plants, weeds or trees are applied on the skin surface. The area is kept dry and the result is noted after 48 hours.

  2. Provocative patch test - this test is used for detection of sensitivity of neomycin, penicillin and benzocaine.

    Provocation of the open patch test is maintained by application of 10 per cent of sodium lauryl sulfate to the test area for one hour. A significant reaction may appear when the patch test is done.

  3. Vapor patch test - this test is applied for volatile substances such as perfumes.

    Apply the vapor or gas to the skin surface under a small glass cup tapped into the skin for 48 hours.

  4. Mucous membrane patch test - this test is used for local sensitizing agents for the mouth as mouthwashes, nicotine and toothpaste.

    A small suction cup containing the test material is applied to the mucous membrane of the lip and kept for one hour. Control is essential in this type of test.

  5. Photo patch test - this test is used for detection of photosensitizing substances such as phenothiazine, sulfa, and photosensitizing plants.

    Patch test is done in the ordinary way for 48 hours where the area is exposed to ultraviolet radiation and then read again after another 48 hours. Control test area is necessary for exclusion of false positive or negative reactions.

Technique of Ordinary Patch Test

Patch testing is available nowadays ready, where the antigen can be applied directly on the testing area. The sites for the tests are usually on the back or inner arms. If these are not available the diluted substance can be applied on gauze and covered by elastoblast.

The reaction may be detected after 30 minutes as in contact urticaria. These are usually read at 48-72 h and again up to 1 week.

If pruritus, pain or irritation occurs, patch testing should be removed and mild steroid may be applied to the area. 

Interpretation of Patch Test

The result of patch test is interpreted as follows:

1+: Erythema only.

2+: Erythema and papules.

3+: Erythema, papules and small vesicles.

4+: Large vesicles, bullae, and severe local reaction besides erythema.

False Reactions

False positive and negative reactions are common in patch testing. This is due to different factors:

  • Low concentration or insufficient amount may give false negative.

  • High concentration and increased amount may cause local irritation.

  • Improper testing as the substance is not fresh, or presence of impurities in the testing substance or the occlusion was not complete.

  • The patient is under antihistamine or systemic steroid will give false negative reaction.

Intradermal Tests

Site used for testing: the injection is made into the superficial layer of the dermis in the flexor surface of the forearm.

Needle used: through a fine bore (26 or 27) needle with its bevel pointing upwards.

Quantity of the solution injected: the quantity, which may be injected, varies from 0.01 to 0.1 ml and routinely 0.05 ml is usually sufficient. 


The test is accomplished by putting the skin under tension with the fingers of one hand: the other hand inserts the needle attached to the tuberculin syringe containing the test material.

Interpretation of the test

Time of reading the test: The optimal time for reading the reaction naturally varies with the pharmacological agent or the type of immunological reaction. Most such tests are read at either 15-20 min or at 48 h, but it may be important to read the tests at other times, e.g. at 4-12 h or after 4 days.

Control solution: The test solution must always be compared with a control solution injected in a comparable site at the same time.

A positive test may be taken as one that is significantly different from the control. Assessment of what is significant is difficult and varies with the enthusiasm of the tester.

The response can be observed at 15 minutes, for example, after an injection of histamine or after immediate-wheal allergy tests, is a wheal with a surrounding flare.

The wheal is a more accurate measure than the flare. When the test is read at 48h, for example, the tuberculin reaction, the sizes of the indurated papule and of the erythematous reaction should be observed.

The measurement of a wheal is usually made by diameter. The size of the weal is not directly proportional to the dose of the active agent but varies also with the total volume of fluid injected. For accurate quantitative observations weal diameters below 4 mm or above 15 mm cannot be relied upon.

Precautions before doing the test:

  • Antihistamines: Antihistamines may greatly inhibit the immediate wheal tests. For the very long-acting drugs as terfenadine or astemazole, this effect may last as long as 3 weeks.Antihistamines interfere with the development of the wheal and flare reaction and should be stopped before immediate-type skin testing. First-generation antihistamines may be stopped two to three days before testing, but the newer, second-generation antihistamines can affect skin testing results for three to 10 days or longer. Medications with antihistamine properties, such as anticholinergic agents, phenothiazine, and tricyclic antidepressants, also should be discontinued before skin testing. Histamine H2-receptor antagonists (e.g., cimetidine [Tagamet], ranitidine [Zantac]) have a limited inhibitory effect; these medications may be stopped on the day of skin testing.1 Inhaled and short-term systemic corticosteroids generally do not significantly suppress the wheal and flare reaction of immediate-type skin tests.

  • Corticosteroids: Moderate-to-large doses of corticosteroids in contrast may somewhat inhibit patch tests although smaller doses, e.g. Prednisone 10 mg daily, are not necessarily a contra-indication to testing. Steroids do not greatly inhibit the immediate weal tests.

  • Antishock measures should be at hand.



This is a modification of the intradermal test and is convenient for much routine allergy testing. The intradermal injections of prick test solutions may be dangerous.

Technique: A small quantity of the test solution is placed on the skin and a prick made through it with a sharp needle. This should be superficial and not sufficient to draw blood.

The size of the weal and flare 

are measured after 15 min.

Fig. 11. Scratch test



The scratch test resembles the prick test.

Technique: A linear scratch about 1 cm long, but not sufficient to draw blood, is made through the epidermis. This test gives less reproducible results than the prick test.

Modified prick test

This test is slightly more sensitive than the ordinary prick test, but gives no more reproducible results.

Technique: A drop of the test solution is placed on the skin. A needle is then inserted very superficially and almost horizontally into the skin and lifted to raise a tiny tent of epidermis.

Immediate wheal tests


  • These tests are used for detecting IgE antibodies.

  • The passive transfer test may be used to detect circulating IgE, but is not recommended because of the risk of serum hepatitis or AIDS.

  • They are principally used in the assessment of hay fever and asthma and have a limited place in the management of atopic dermatitis.

  • They are disappointing in the diagnosis of urticaria.

  • False-positive and false-negative reactions are common.

  1. Rast &  Elisa Tests

    Rast (Radio-Allergosorbent Test) and ELISA (Enzyme-linked Immunosorbent Assay) are alternative methods to detect and measure circulating antibodies.

    Although widely used in the past, serum measurement of the total IgE level is unhelpful in the diagnosis of allergy. Of more clinical use are assays for specific IgE antibodies to suspected allergens.

    Assays for IgE antibodies specific to common airborne and food allergens are readily available. IgE antibody tests for venom and drugs have less clinical utility and are not routinely used. RAST was the first widely employed method of detecting IgE antibodies in blood that are specific for a given allergen.

    hat include a reference curve calibrated against standardized IgE are preferred. It is important to select a reliable laboratory to perform RAST testing.

    In general, RAST and other laboratory methods for IgE testing are highly specific but somewhat less sensitive than percutaneous tests. Results of laboratory testing for food-specific IgE are generally poor, even less helpful than those for percutaneous skin testing.

    RAST or other laboratory testing is typically considered when skin testing is inconvenient or difficult to perform. Most primary care physicians do not have immediate access to a clinical skin testing laboratory, so RAST may be easier to obtain. Some patients cannot undergo skin testing because of skin disease that would obscure wheal and flare results (e.g., extensive atopic dermatitis) or because they cannot stop taking medications that suppress the skin test response. In cases of life-threatening allergy (e.g., anaphylaxis), laboratory testing is sometimes used as a proxy result, keeping in mind its limited sensitivity.

    Percutaneous testing can help establish the correct diagnosis and identify the offending allergens (pollen, mold spores, dust mites, cockroaches, or household pets). Allergen avoidance measures often are difficult to implement and costly. After specific testing, avoidance measures can be targeted to allergens to which the patient is known to be allergic.

    Allergen immunotherapy is another option in refractory cases of allergic rhinitis not amenable to the usual control measures. Like allergen avoidance, it can involve a lot of labor and expense. Specific allergy testing can identify patients likely to benefit from immunotherapy and provide guidance about which allergens to include in the therapy regimen. Allergen immunotherapy may be especially beneficial when avoidance and medications no longer control the patient's symptoms. 

     Several closely related variants are marketed (e.g., modified RAST, Quidel QuickVue One-Step Allergen screen, Pharmacia Immunocap). Quantitative assays test.

    RAST correlates well with skin testing. It is justified in testing very young children, and with allergens associated with risk on prick testing (e.g. drugs).

  1. Oral provocation tests

    These tests must be carried out with care and is only valuable if the test is properly controlled and the patient is co-operative and well motivated. The administration of a drug, food or chemical by mouth may sometimes be called for to confirm the diagnosis of an eruption or to establish its exact cause.


  • Drug eruption. To determine the cause of a drug eruption or to isolate one from a number of drugs or ingredients of a compound drug. It may be a valuable method of proving the cause of a fixed drug eruption but should rarely, if ever, be used if the reaction has been of a generalized or acute nature.

    It is applicable only when the drug given and the dose chosen are unlikely to provoke a severe reaction in the patient.

  • Atopic eczema

  • Chronic or recurrent urticaria.

  • Food allergy. The re-introduction of specific foods, or additives such as:

    Tartrazine, benzoates and anti-oxidants one at a time, is an established part of exclusion, elimination and challenge diets. It is important that the role of the suspect food is subsequently confirmed by reintroducing it in a disguised form to avoid identification by the patient.

  1. Elimination and exclusion tests

    These tests are used to detect the blamed food, additives or beverages that are suspected to cause dermatitis. Exclusion of the suspected material for few days and observing the skin lesion may give an indication of the effect of the eliminated material.

  1. Wood‘s light

    This is an ultraviolet lamp with Wood‘s filters, which produces a wavelength about 3650 Â. Wood‘s light is an important investigative tool in diagnosis and treatment of specific skin diseases.

    Wood‘s lamp may be used to help in the diagnosis of the following lesions:

    Fungal infections: Tinea capitis caused by Microsporon species gives bright blue-green fluorescence. It should be noted that Tricophyton tonsurans and Tricophyton violeceum types of ringworm do not give fluorescence.
    Erythrasma: gives a coral-red fluorescence.

    Pityriasis versicolor lesions when examined in a dark room with Wood‘s light appear as sharply accentuated lesions.

    Bacterial infections: Pseudomonas pyocyanea gives a yellowish-green color due to pyocyanin.

    The acne bacillus causes a coral fluorescence in the follicles possibly due to porphyrin production. Erythrasma gives coral- red or pink-orange fluorescence.

    Detection of pigmentary disorders:

    Wood‘s lamp can be used to determine the depth of melanin in the skin, since variations in epidermal pigmentation are more apparent under Wood‘s lamp than under visible light. Wood‘s light accentuates contrast between pigmented and non-pigmented skin and separates hypopigmented from totally non-pigmented areas as in vitilligo and albinism.

    Detection of porphyrins:

    Porphyrins in urine when examined in dark field by Wood's light, gives red color or pinkish orange. Porphyrins in feces, blister fluid in porphyria lesions, the teeth in erythropoietic porphyria and blood protoporphyria give also the same fluorescence.

    Erythropietic porphyria can be also diagnosed by the fluorescence of red cells.

    Tetracycline: deposits in the growing enamel teeth of children that produces a typical yellow color of the teeth under Wood‘s light illumination.

    Malignant tumors of the skin especially squamous cell carcinoma gives bright-red fluorescence.


    Medications, industrial compounds and other fluorescent materials can be detected specifically by Wood‘s light.


    The purpose of prenatal diagnosis is detection or exclusion of a hereditary disease or congenital defect in utero. The option of an elective abortion of affected pregnancies can help parents at risk of having affected children to have a normal offspring in the future.

    Hereditary skin diseases if diagnosed in early pregnancy may help very much to minimize social, psychological, and financial states. It may help in planning of having normal babies instead of repeated abortions, miscarriage or malformed deliveries.

    If the fetus is aborted after a positive diagnosis, a careful post-mortem examination should be carried out in order to confirm the diagnosis and search for other possible congenital abnormalities.

    Methods of  Diagnosis

    Amniotic fluid and its cells are used for diagnosing a variety of metabolic diseases, morphological, biochemical and cytogenic.

    Ultrasonography: is a powerful tool for the detection of central nervous system and skeletal disorders.

    Fetoscopy: this is a technique that involves the insertion of a fibro-optic endoscope into the pregnant uterus.

    Amniocentesis: is a convenient and relatively safe method of obtaining amniotic fluid and its cells for morphological, cytogenetic and biochemical investigations. This test is usually performed at 16 weeks of gestation.

    Fetal skin biopsy: helps in the detection of morphological or immuno-histochemical abnormalities.

    Enzymatic assay

    DNA Examination: DNA test helps to detect any genetic abnormalities.

    Cyto-diagnosis :

    Examination of scrapings from the lesion or the contents of the vesicles can help in reaching diagnose of certain skin diseases. Cytological smears should be taken from early fresh lesions.

    Thin smear on a clean glass slide is left to dry, stained with Wright‘s stain, hematoxylin and eosin or Giemsa stain. This can be examined with the low power and then by the high power to have an idea about the content of the smear. 


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