Diagnosing Allergy to Latex
OHCP and patients who relate a history of papular, pruritic (itchy) rash of the skin; urticaria, angioedema, and rhinoconjunctivitis; coughing, shortness of breath, or wheezing; and/or a drop in blood pressure following exposure to latex should be suspected of latex allergy. The diagnostic algorithm for latex allergy entails obtaining a thorough medical history, skin-patch testing, serum IgE measurement, and glove provocation testing.7,13,28,29
Obtaining a complete medical history is the first step in diagnosing latex allergy. As noted earlier, certain patient populations (i.e., those with neural tubal defects and occupational exposure) are at higher risk for latex allergies than the general population. Other risk factors include a history of atopy, multiple surgeries, previous hand dermatitis of any kind, and allergies to foods known to have allergens that cross-react with latex.13,30
Many latex proteins, collectively called pathogenesis-related (PR) proteins, serve to protect the rubber tree from a variety of environmental threats such as infections (fungal, bacterial, and viral), wounding, and chemical insults.31 These same proteins are also expressed in a number of other plant species.32 For example, the latex protein ß-1,3-glucanase shares high association with the ß-1-3-glucanase proteins found in avocado, banana, chestnut, and kiwi.
Other latex PR proteins share moderate association with analogous proteins in apple, carrot, celery, melon, papaya, tomato, and potato. Low or undetermined association exists between still other latex PR proteins and many other fruits and vegetables, e.g., turnip and zucchini. 33 It is estimated that a patient with a history of fruit allergy has an 11% risk of concurrent latex allergy.34Conversely, up to 50% of patients with latex allergy are hypersensitive to some plant-derived foods.5,13,35
Skin-patch Testing (SPT)
SPT is reliable for diagnosing delayed hypersensitivity reactions to latex additives and helps to differentiate between ICD and ACD. It is performed by applying allergen samples to intact skin and covering them with a dressing. The patient is checked for skin reaction at 30 minutes, 24 hours, and 48 hours.7,13 Swelling, redness, or blistering characterize a positive test.
If the test is negative, the site is reexamined again at 72 and 96 hours because weak reactions may appear later. A refinement of the technique, the thin layer rapid use epicutaneous (T.R.U.E.) test (SmartPractice, Phoenix, AZ, USA), has been licensed by the FDA and is available commercially. The T.R.U.E. test consists of a pre-prepared testing strip containing 35 of the most common contact allergens, including four rubber screening mixes and mercaptobenzothiazole.36.
Radioallergosorbent Test (RAST)
RAST is a quantitative measurement of allergen-specific IgE antibodies. It is the test of choice to confirm latex-related immediate hypersensitivity reactions.13 There are at least five FDA-licensed assays available (e.g., Alastat [Diagnostic Products Corporation, Los Angeles, CA, USA], ImmunoCAP [Phadia AB, Portage, MI, USA], CLA Allergen-Specific IgE Assay [Hitachi Chemical Diagnostics, Mountain View, CA, USA], and HY TECH-288 [Hycor Biomedical Incorporated, Garden Grove, CA, USA]). Their sensitivity and selectivity varies from 50-90% and 80-87%, respectively.13
Glove Provocation Testing (GPT)
GPT is useful when a person’s clinical history is inconsistent with RAST results.13 During the test, the patient wears one finger of a latex glove. If there is no urticarial reaction after 15 minutes, the exposed surface area is increased (i.e., two fingers and so on). A negative GPT is confirmed by the absence of urticaria after wearing a full glove for 15 minutes.7,13 A positive GPT is confirmed by the presence of urticaria. Because of variations of latex content in gloves, GPT may be unsafe in highly sensitized persons.5