Urticaria Diagnostics

Laboratory Tests and Ancillaries

Routine lab testing is not indicated but may be considered in the following patients with:

• History or physical examination findings concerning a systemic condition: Complete blood count (CBC) with differential, liver function tests (LFTs), erythrocyte sedimentation rate (ESR), thyroid-stimulating hormone (TSH)
• Angioedema presentation: Measurement of C4, C1 inhibitor antigenic level and function, and C1q
• History consistent with allergen-induced contact urticaria: Skin testing with allergen extracts and screening for dermatographism
• Fever, arthralgias, and elevated ESR, or urticarial lesions with residual pigmentation, ecchymoses and/or lesions lasting >24 hours at a single location: Skin biopsy to evaluate for urticarial vasculitis
• Acute urticaria suspected of food or contact allergy: Skin prick or serum testing for allergen-specific IgE

Acute Urticaria  

Routine laboratory workups are not required except when the cause of the urticaria points to a type I food hypersensitivity or other triggering factors like medications (eg nonsteroidal anti-inflammatory drugs [NSAIDs]). It is advisable to exclude anaphylaxis prior to proceeding with further urticaria workup, as it may need urgent management.  

Chronic Urticaria  

Diagnostic examinations are based on the patient’s history and physical examination. Assess disease activity of chronic urticaria. Several guidelines recommend using the Urticaria Activity Score (UAS) system in assessing disease severity and treatment effectivity in patients with wheals.

The summation of scores of symptoms during a 7-day period (UAS7)

• 0 = no wheals, no pruritus
• 1 = mild wheals (<20 wheals within 24 hours) + mild pruritus (non-troublesome)
• 2 = moderate wheals (20-50 wheals within 24 hours) + moderate pruritus (troublesome but does not interfere with daily activities or sleep)
• 3 = intense wheals (>50 wheals within 24 hours or large confluent wheals) + intense pruritus (severely troublesome, interferes with daily activities and sleep)

The Chronic Urticaria Quality of Life questionnaire (CU-Q2oL) is the recommended quality of life tool to assess the quality-of-life impairment specific to chronic spontaneous urticaria. While Angioedema-specific Quality of Life tool (AE-QoL), Urticaria Control Test (UCT), Angioedema Control Test (AECT) and Angioedema Activity Score (AAS) may also be used to assess a patient's quality of life and disease status, which may help in treatment decisions.  

Chronic Spontaneous Urticaria  

The goals of diagnostic work-up include confirming the diagnosis and ruling out differential diagnoses, identifying underlying causes, conditions that affect disease activity (eg food, drugs [NSAIDs], stress, infections), comorbidities, and consequences of chronic spontaneous urticaria (anxiety, depression, sexual dysfunction, sleep disturbances), assessing predictors of disease course and treatment response, and monitoring disease activity (UAS, UAS7, AAS), impact (CU-Q2oL, AE-QoL), and control (UCT, AECT).  Further tests are requested if indicated by the patient’s history, physical examination, and basic tests, most notably in patients with chronic and/or on-and-off disease presentation.  

Chronic Inducible Urticaria  

The goals of diagnostic work-up include ruling out differential diagnoses, identifying subtypes, and determining trigger thresholds. Provocation threshold measurements are used to assess disease activity and control, while the UCT is used to determine how well the disease is prevented from recurring.

Autoimmune Chronic Spontaneous Urticaria (ACU)  

Proposed gold standard for diagnosis of ACU (combination of all three parameters):

• Positive bioassay (eg basophil histamine release assay [BHRA], basophil activation marker expression) and
• Positive autoreactivity (eg positive autologous serum skin test [ASST]) and
• Positive immunoassay for specific IgG autoantibodies against FcεRIα and/or anti-IgE