Toxic necrotizing epidermolysis bullosa drug rash skin manifests as total epidermal necrosis and subepidermal macules formation. Most drugs have the potential to cause drug rashes, including herbal medicines, but the more antigenic ones cause the most. Most of them are sulfonamides, salicylates, antipyretic and analgesic drugs such as pautazone and aminopyrine, phenolphthalein, penicillin, tetracycline, barbiturate, phenytoin sodium, etc. In addition, there is a greater risk of drug rash in organisms with congenital allergic diseases and in patients with diseases of vital organs. What are the tests and diagnoses of total epidermal necrosis and subepidermal maculoplasia? 1. Routine blood tests: eosinophils are often increased, leukocytes may be increased, and sometimes leukocytes, erythrocytes and platelets are also decreased. 2.Liver and kidney function tests: if there is a reaction of liver and kidney function, the corresponding relevant tests should be performed. 3, drug allergy test (1) in vivo test: ① patch test: the positive rate in drug rash is low, has reported a positive rate of 31.5%, the positive rate for phenobarbital, phenytoin sodium, carbamazepine is higher. The patch test is safe and easy, and if positive, there is no need to do intradermal test and excitation test again. The concentration of penicillin and cephalosporins can be chosen from 10% to 20%, and the positive rate is higher with petroleum jelly or 70% alcohol as the base, and the concentration of carbamazepine should be 3% to 10%. ② Intradermal test: mainly used to detect type I metaplasia, the positive rate can reach 89.7%, the positive rate of penicillin, cephalosporins and gold salt preparations is higher. It should start from low concentration, and gradually increase the concentration when the result is negative, which will be safer. ③ excitation test: after the drug dermatitis subsides for a certain period of time (1~2 months), the drug is administered again with the allergenic drug imitating the original route of administration to observe the reaction to make a judgment. This method is reliable, but very dangerous and cannot be applied to severe drug rashes. In rash-type drug rashes, the provocation test can develop into exfoliative dermatitis in severe cases. The method can be used for fixed erythema and no potential risk of erythema type, the amount of medication to be used varies from person to person, in the heavier to stimulate the amount of medication to be small, the lighter the amount of medication can be large, generally the first stimulation of the amount of medication for 1/10 of the normal amount or less, if no response, then again to stimulate the amount of medication increased to 1/10 ~ 1/4, and then in turn 1/2 until the full amount, each stimulation should be observed 6 ~ 24h, if no response to another stimulation. Subjects should be closely observed. (2) In vitro tests: ① Specific antibody detection in serum: antibodies in serum include IgG, IgM, IgA and IgE, detected by radioallergo-sorbentassay (RAST), microhemagglutination test (hemagglutination) and enzyme-linked immunosorbent assay ( enzyrme-linkedimmunosobentassay, ELISA), RAST is the assay used to detect IgE in type I allergic reactions to drug rash. ② basophil degranulation: using patient basophils with sensitizing drug (direct method) or using rabbit basophils with patient serum plus sensitizing drug (indirect method) to degranulate them to check drug allergens. Only used for type I allergic reaction. Lymphocyte transformation test (SLTT): Small lymphocytes sensitized in peripheral blood are stimulated by drugs (specific antigens) and cultured in test tubes for 2-3 days, which can be transformed into lymphoblastoid cells and undergo proliferation and division. SLTT was found to be positive in 60% of patients with cotrimoxazole allergy, and a domestic study proved its positivity rate of 53.7%. Although the sensitivity of SLTT is low, but its specificity is high, so far there is no false positive reports, so it is not lost as an experimental diagnostic method of drug rash. ④Macrophage wandering inhibition test (MIF test): patient lymphocytes + guinea pig macrophages + the drug under test were incubated for 24h and the results were observed. The positive rate was found to be 53%-70%. ⑤ Lymphocyte toxicity test: in the antiepileptic drugs (such as phenobarbital, phenytoin sodium, carbamazepine) and rash drug rash caused by sulfonamides, as it is considered to be related to toxicity caused by defects in certain enzymes in the detoxification process of drug metabolites. Therefore, this test can be used to detect drug toxicity by incubating the suspected drugs with the patient’s lymphocytes in vitro and observing the number of lymphocyte deaths. The results were positive in 7 cases of sulfonamide rash and 40 out of 50 cases of antiepileptic rash. This test is still in the research phase.