Laboratory Studies
ED diagnosis and management depends on the history and the physical examination. [30] Results of laboratory tests sent from the ED are not generally available in a useful time frame. Several types of diagnostic studies are useful in nonemergent evaluations.
Total serum IgE may be elevated in patients with type I allergy, but it is neither sensitive nor specific.
Radioimmunoassay test (RAST) results for latex-specific IgE range from 50-100% sensitive and 63-100% specific. Predictive value depends on the exact test used, the patient population, and the source of allergen. RAST can be a useful and safe confirmatory test in patients with suggestive clinical histories. The sensitivity and specificity are improving with newer-generation testing methods. [31]
Enzyme-linked assays of latex-specific IgE (ELISA) may serve the same purpose. [32]
Genomic profiling may become a useful tool for predicting risk, guiding therapy, and understanding pathophysiology in latex allergy. [33]
Other Tests
Skin patch testing is useful in identifying specific allergens in patients with type IV hypersensitivity to latex products. [34]
Skin prick testing (SPT) with latex extracts is sensitive, specific, and rapid; however, it carries the risk of anaphylaxis. [35] Significant variability in the allergen content of extracts continues to limit the reliability and reproducibility of this test. SPT is an important step in the diagnosis of IgE-mediated occupational allergic disease. It is utilized in latex allergy, however, the outcome is related to the quality of allergen extracts. Unfortunately, there are no standardized extracts commercially available in the United States. There are some standard extracts in Europe. These were developed with natural rubber protein latex for oral testing and the results show that both protein and antigen contents of the SPT solution varies remarkably depending upon the manufacturer. [36]
Testing with glove fingertips applied to the patient's skin is useful when the history is consistent with latex allergy but the blood tests are negative. It carries the risk of anaphylaxis in type I-sensitized patients.
Specific IgE measurement through ImmunoCAP and the Immuno Solid-phase Allergen Chip (ISAC) has also been utilized. The ImmunoCAP system has the following eight single recombinant latex allergens available: rHev b 1, 3, 5, 6.01, 6.02, 8, 9, and 11.
The ISAC test includes less antigens and relies on immunofluorescence anti-IgE. It includes rHev b 1, 3, 5, 6.01, and 8. These tests in general are very specific but not as sensitive. The most important selective allergen is Hev b 8, which is common between these two tests. ImmunoCAP is a more sensitive test, however. This has to be correlated with occupational exposure.
Flow cytometry to determine basophil activation is another alternative method to diagnose latex allergy. It is based on the determination of activated basophils expressing CD 63. The combination of flow cytometry and ImmunoCAP has been shown to be associated with accurate identification of natural rubber allergy to latex in patients.
The blood use test has also been utilized. It is highly sensitive when used with vinyl or nitrile gloves on one hand as a negative control. Finally, the latex allergy challenge test has been used on patients with respiratory symptoms and has shown high sensitivity. Mucus and cutaneous tests are the most reliable, with specificity of almost 100%. The conjunctival allergen challenge showed sensitivity and specificity of 92%–100%.
Latex allergens can be recovered from environmental air, laboratory colds, and subtle dust on the surface of laboratories where powdered rubber latex gloves are used. Samples can be obtained from air conditioning units, but have to be collected on a special filter for adequate analysis. [36]
Diagnosis of latex allergy continues to be challenging. SPT may achieve 62% sensitivity with a homemade solution. Skin tests specific for Hev protein b, 2, 5, 6.01, and 13 have 60% reactivity. In a murine model, contact dermatitis was the striking feature and it is associated with an increase in IgE. This suggests that latex sensitivity in humans can be a combination of type I and type IV reactions in some situations. [37]
Procedures
If type I latex allergy is suspected, all procedures should be performed with latex-free instruments, devices, and protective clothing.
Preprocedure screening by history should include risk factors such as occupational and nonoccupational risk groups, tropical fruit allergy, and atopy as well as documented latex allergy.
