Acute spontaneous urticaria with a duration of illness less than 6 weeks does not require laboratory diagnosis. In most cases, these conditions are nonallergic urticaria, which often occurs associated with infections. This usually resolves spontaneously within one to two weeks. In contrast, chronic spontaneous urticaria requires extended diagnostics. Laboratory parameters of the 1st order – obligatory laboratory tests.
- Small blood count
- Differential blood count [detection of basophilic granulocytes decreased the likelihood of healing].
- CRP (C-reactive protein)
- Liver parameters – alanine aminotransferase (ALT, GPT), aspartate aminotransferase (AST, GOT), glutamate dehydrogenase (GLDH) and gamma-glutamyl transferase (gamma-GT, GGT), alkaline phosphatase, bilirubin.
- Renal parameters – urea, creatinine, cystatin C if necessary.
Laboratory parameters 2nd order – depending on the results of the history, physical examination and mandatory laboratory parameters – for differential diagnostic clarification.
- Total IgE; allergen-specific IgE (RAST).
- Allergological testing
- Epicutaneous test (synonyms: patch test, patch test) – in this test, a patch is applied to the patient’s skin containing various allergens; after two to three days, the patch can be removed and the test assessed
- Provocation testing (see below “Diagnosis of spontaneous urticaria subtypes”).
- Cryoproteins (cryoglobulins, cryofibrinogen, cryoagglutinins) – in suspected cold contact urticaria.
- Histamine, tryptase, eosinophil cationic protein (ECP).
- Infectious serology
- Helicobacter pylori serology
- Hepatitis B-/C-Serology
- Stool examination for pathogenic germs, parasites, worm eggs.
- Antinuclear antibodies (ANA) – for suspected systemic lupus erythematosus (SLE).
- Skin biopsy
Diagnosis of spontaneous urticaria subtypes.
| Forms | Subforms | Definition | Provocation testing | Complementary tests |
| Physical urticaria | Cold contact urticaria | Triggering factors may include cold objects, air, liquid, wind | Cold provocation and sulfur testing (ice cubes, cold water, etc.) | Differential blood count and inflammatory parameters (BKS or CRP), cryoproteins, to rule out infections or, other diseases, respectively. |
| Delayed pressure urticaria | Triggering factor is static pressure; wheals appear with a 3-12 hour delay | Pressure test and threshold test | ||
| Heat contact urticaria | Triggering factor is localized heat | Heat provocation test and threshold test | – | |
| Light Urticaria | Triggering factor is UV and/or visible light. | Test with UV light and visible light of different wavelengths incl. threshold test | Further diagnostics to exclude other light-induced dermatoses. | |
| Urticaria factitia/symptomatic urticarial dermographism. | Triggering factor is shear forces; wheals appear after 1-5 minutes | Dermographism-triggering test (sweep a smooth, blunt object (e.g., closed ballpoint pen or wooden spatula) moderately hard across the skin) and swelling test | Differential blood count and inflammatory parameters (BKS or CRP), cryoproteins, to rule out infections or, other diseases, respectively | |
| Vibratory urticaria/angioedema. | Triggering factor is vibration (e.g., jackhammer) | Forearm (inner side) test: vortex for 10 minutes, 1,000 rpm; reading time: 10 minutes after test. | – | |
| Other types of urticaria | Aquagenic urticaria | Triggering factor is water | Application of wet, body-temperature cloths to the skin for 20 min | – |
| Cholinergic urticaria | Triggered by elevation of core body temperature (e.g., from exertion, spicy foods) | Sports provocation test: exercise machine, e.g., bicycle ergometer or treadmill. Exercise for 30 minutes, increase pulse rate by 3 beats/min every minute.Positive test = wheal.If the test result is positive, wait > 24 hours and perform the hot bath provocation test. Hot bath provocation test (42 ºC bath): measure body temperature. ; if body temperature has risen ≥ 1 °C above baseline, continue bath for 15 minutes.Reading time: during test, immediately after test, and 10 minutes after test. | – | |
| Contact urticaria | Triggered by contact with urticariogenic substances | Cutaneous provocation test, skin test with immediate reading, for example, prick test (see above) | – |