When testing for its less intense form (fixed solar urticaria), phototesting should be conducted only in the areas where the hives have appeared to avoid the possibility of getting false-negative results.A third form of testing is the photoprovocation test which is used to identify disorders instigated by sun burns. The process of this test involves exposing one area of a patients arm to certain dosage of UVB radiation and one area on the other arm to a certain dosage of UVA radiation. The amount of radiation that the patient is exposed to is equal to that "received in an hour of midday summer sun." If the procedure produces a rash, then the patient will undergo a biopsy. Finally, there are laboratory tests which generally involve procedures such as blood, urine, and fecal biochemical tests. In some situations, a skin biopsy may be performed. Classification
Solar urticaria, due to its particular features, is considered to be a type of physical urticaria or light sensitivity. Physical urticaria arises from physical  factors in the environment,  which in the  case of solar urticaria is   UV radiation or light. SU may be classified based on the wavelength of the radiative energy that causes the allergic reaction; known as Harbers classification, six types have been identified in this system. Type I solar urticaria is caused by UVB (ultraviolet B) radiation, with wavelengths ranging from 290 to 320 nm. Type II is induced by UVA (ultraviolet A) radiation with wavelengths that can range from 320 to 400 nm.
In one 6-year-old patient antibodies to GABA-producing enzyme glutamate decarboxylase were detected. See also
Stiff person syndrome

References


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