Routine tests available for the diagnosis of allergy to natural rubber latex (NRL) and rubber chemicals

A diagnosis of Type I NRL allergy should be made on the basis of clinical history plus positive investigation.
Test results should not be interpreted in isolation. In particular, the presence of allergen-specific IgE indicates that allergen has been encountered, but does not necessarily indicate an allergic response. In vitro tests measure circulating IgE, which may not reflect specific IgE bound to mast cells. So, a negative test can occur in a symptomatic individual, and a positive test in an asymptomatic individual.
There are unresolved technical issues regarding the standardisation of current tests.

Test	Method	Indication	Risk
Skin prick test (SPT)	This is the most sensitive and specific diagnostic method currently available. Commercial extracts of graded strength may be used. Alternatively, a test reagent can be prepared by soaking small pieces of high protein NRL glove in water or saline, although allergen content may vary with this method. It is important to use negative (eg saline) and positive (eg histamine) controls at the same time. A positive test will produce a wheal at least 3mm larger than the negative control.	Assessment of hypersensitivity to NRL protein allergens (Type I hypersensitivity)	Small risk of anaphylaxis. Resuscitation drugs and equipment should always be available.
Allergen-specific IgE -- previously known as RAST, now termed (F)EIA (fluoro) enzyme immunoassay	In vitro method of measuring latex-specific IgE from a blood sample. Sensitivity (lower than SPT) and specificity vary, dependent on allergen content of source material, cross-reactivity with eg food-specific IgE, and assay threshold limits.	Useful if SPT not feasible, or if contraindicated. The presence of allergen-specific IgE does not always correlate with clinical symptoms or risk of future events.	Nil
Provocation (use) test	Wearing a finger of NRL glove on wet skin for 15 minutes, with vinyl glove as control. If no wheal (urticaria) is produced, a whole glove can be used, with exposure time lengthened if necessary.	May be considered if clinical suspicion of NRL allergy with negative allergen-specific IgE and SPT.	There is a higher risk of anaphylaxis with this method, and again resuscitation equipment should always be available.
Patch test	Allergens are applied under occlusion to the back for 48 hours and then removed. Readings are generally taken at 2 and 4 days. A positive reaction will produce erythema (red skin), oedema and, if severe, vesiculation.	For diagnosis of Type IV hypersensitivity to rubber chemical additives, eg thiurams, carbamates and mercaptobenzothiazoles - contact allergic dermatitis. Type IV allergy to latex has been described in a very small number of patients.	Small theoretical risk of sensitisation

References

Deacock S. Latex allergy, CPD Bulletin Immunology and Allergy 2001; 2: 8-11
Wakelin SH, White IR. Natural rubber latex allergy . Clin Exp Dermatol 1999; 24:245-8
Pridgeon C, et al. Assessment of latex allergy in a healthcare population: are the available tests valid? Clin Exp Allergy 2000; 30: 1444-9