Hives can be diagnosed by a number of medical professionals, however most diagnoses are made by family physicians (general practitioners). Other doctors that may be consulted include:
- Paediatricians (if a child develops hives)
In general, there are no specific tests available for the diagnosis of hives. This is due to the nature of triggers, which in many instances is non-specific or idiopathic. In some cases, a trigger can be identified – for instance a type of medication. Discontinuation of the medication can determine whether it is a trigger if an outbreak of hives clears once being discontinued. If it does not, the medication is not likely the cause.
In order to try and determine an underlying cause of hives, such as an allergic reaction, a doctor will wish to obtain a detailed medical history and conduct a symptom discussion during the consultation, followed by a thorough physical examination.
Questions a doctor may ask during the consultation include:
- How long ago did symptoms first begin?
- How did the markings on the skin look when they first appeared?
- Have the markings changed in any way (such as size or shape) since?
- Has anything appeared to make symptoms better or worse before this consultation?
- Are the skin markings itchy, burning or stinging at all?
- Have any markings disappeared without leaving another marking such as a bruise before this consultation?
- Have any allergies been diagnosed? If so, what?
- Has a similar skin problem ever developed or occurred in the past?
- Have any new foods been eaten for the first time?
- Have any new products, such as cleaning detergents been introduced for the first time?
- Have any insect bites or stings occurred recently?
- Are any new medications (prescription or over-the-counter) currently being taken (including herbal supplements)?
- Has a new pet been introduced into the home?
- Has a family member ever had a similar type of skin problem?
- Do any family members have any known allergies?
- Have there been any other noted health changes recently? (i.e. a fever or a little unintended weight loss)
- Have any at-home treatments been applied at all? Have they improved or worsened symptoms?
A doctor will then conduct a physical exam and evaluate the skin markings (those that are present). If allergies are suspected, a skin prick test may be performed to determine the substance causing the reaction. It may be that a trigger is fairly obvious to pinpoint, such as a reaction occurring in a short space of time following the ingestion of shellfish or peanuts, or exposure to sunlight or water, after a scratch has occurred to the skin or following strenuous exercise.
Once a trigger allergen is determined, a doctor will advise against contact with or ingesting a particular foodstuff, or other products made from or containing the substance. If deemed safe enough to do, an oral food test may be requested where a suspected allergen will be given to the affected individual to eat (in a measured amount) to induce a hive reaction. The same type of oral test can be done with medications as well (a cautious drug challenge). If the risk of severe reactions, such as anaphylaxis is too high, these tests may not be performed, but any that are will be carefully monitored for their duration, often with emergency equipment or medication on hand.
Blood tests may also be recommended to assess for particular illnesses known to be associated with hive outbreaks, as well as to check blood proteins if there is a potential hereditary pattern (as in the case of hereditary angioedema). A urine sample can also sometimes be recommended.
Extensive testing is not normally favoured by medical professionals in the case of mild hive outbreaks or a single occurrence having taken place. (12) Chronic hives are not commonly linked with an allergic reaction (due to the frequency of recurrences – often for more than 6 weeks). It is more likely that a cause is not external in nature. Relevant tests will be done to determine an underlying cause which can be an autoimmune disease or other medical disorder.
Tests to diagnose hives
Tests which may be recommended (where relevant) in the case of chronic hives may include:
- Blood tests (to check for signs of anaemia)
- Thyroid function test (to assess any signs of an overactive or underactive thyroid – hyperthyroidism or hypothyroidism)
- Liver function tests
- ESR (erythrocyte sedimentation rate) test (to assess any immune system abnormalities)
- Stool (faeces) sample (to assess for or identify any parasites causing an infection)
Tests for angioedema may include:
- Blood tests: C1 esterase inhibitor test (this test checks complement protein levels and helps to determine any underlying reasons for swelling) and complement components (C2 and C4) to assess for any deficiencies. Low levels of these components can show signs associated with swelling and inflammation in the body.
In the case of solar hives (urticaria), tests may be recommended in order to make a diagnosis. These can include:
- Photo-testing: A doctor or allergist may assess skin reactions when exposed to UV light from a sun lamp, using a variety of different wavelengths. The wavelength that the skin reacts to will be used to determine the nature of the sun allergy.
- Patch testing: Certain substances (a suspected sensitizer agent which may trigger a reaction) is applied to the skin and covered with a patch or dressing for a period of time (about 24 to 48 hours) (13). The area will then be evaluated to assess a potential reaction. Skin may then be exposed to UV light (radiation) from a sun lamp. If skin reacts, a diagnosis for solar hives can be made.
- Blood tests: Autoimmune or metabolic clues in symptoms may be tested for with blood samples (and sometimes skin biopsies) to try and determine an underlying cause.
Tests for cholinergic hives
- An exercise challenge test: A doctor will request the patient to perform an exercise routine in order to attempt to stimulate a similar reaction. Medical instruments may also be used to take various measurements during the challenge.
- A passive warming test: A doctor will use warm water or increased room temperature to raise the patient’s internal body heat temperature and observe a possible reaction during the exposure test.
- A methacholine skin challenge test: A non-selective muscarinic receptor, methacholine will be injected in order to stimulate the parasympathetic nervous system and observe a potential reaction.
12. US National Library of Medicine - National Institutes of Health. May - June 2013. Diagnosis of urticaria: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3667285/ [Accessed 29.08.2018]
13. US National Library of Medicine - National Institutes of Health. November - December 2013. Patch Tests: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3900336/ [Accessed 29.08.2018]