Variables in Allergy Skin Testing

Skin testing versus in vitro testing in the evaluation of aeroallergy: The great debate

When one examines reviews regarding diagnostic allergy testing, it generally is noted that the advantage of skin testing is that it uses testing to an end organ, is less expensive, is more sensitive, and provides immediate results, which are easily visualized by the patient. In the case of in vitro testing, it is thought to be more helpful for patients with dermographia or widespread dermatitis, is not affected by H1 or H2 antagonists, and is thought to be safer than skin testing. This may not be entirely correct because studies actually demonstrated phlebotomy to be associated with more morbidity than skin-prick testing. Other concerns regarding both tests include allergen quality, the need from proficiency testing, and the fact that these tests should be used for corroborating a diagnosis as opposed to a screening test for allergy.

Skin prick/puncture testing in North America: a call for standards and consistency

BACKGROUND

Skin prick/puncture testing (SPT) is widely accepted as a safe, dependable, convenient, and cost-effective procedure to detect allergen-specific IgE sensitivity. It is, however, prone to influence by a variety of factors that may significantly alter test outcomes, affect the accuracy of diagnosis, and the effectiveness of subsequent immunotherapy regimens. Proficiency in SPT administration is a key variable that can be routinely measured and documented to improve the predictive value of allergy skin testing.

METHODS

Literature surveys were conducted to determine the adherence to repeated calls for development and implementation of proficiency testing standards in the 1990's, the mid-2000's and the 2008 allergy diagnostics practice parameters.

RESULTS

Authors publishing clinical research in peer-reviewed journals and conducting workshops at annual scientific meetings have recommended proficiency testing based primarily on its potential to reduce variability, minimize confounding test results, and promote more effective immunotherapeutic treatments. Very few publications of clinical studies, however, appear to report proficiency testing data for SPT performance. Allergen immunotherapy recommendations are updated periodically by the Joint Task Force on Practice Parameters representing the American Academy of Allergy, Asthma and Immunology (AAAAI), the American College of Allergy, Asthma and Immunology (ACAAI), and the Joint Council of Allergy, Asthma and Immunology (JCAAI).

CONCLUSIONS

Despite consensus that all staff who perform SPT should meet basic quality assurance standards that demonstrate their SPT proficiency, the gap between recommendations and daily practice persists. By embracing standards, the accuracy of SPT and allergy diagnosis can be optimized, ultimately benefiting patients with allergic disease.

Advertisements impact the physiological efficacy of a branded drug

We conducted randomized clinical trials to examine the impact of direct-to-consumer advertisements on the efficacy of a branded drug. We compared the objectively measured, physiological effect of Claritin (Merck & Co.), a leading antihistamine medication, across subjects randomized to watch a movie spliced with advertisements for Claritin or advertisements for Zyrtec (McNeil), a competitor antihistamine. Among subjects who test negative for common allergies, exposure to Claritin advertisements rather than Zyrtec advertisements increases the efficacy of Claritin. We conclude that branded drugs can interact with exposure to television advertisements.

Variability in skin prick test results performed by multiple operators depends on the device used

Background

The variability of skin prick test results when carried out by multiple users has not previously been assessed across different devices or between different sites on the body. Such multiuser variability has important implications for clinical practice.

Objectives

We assessed the variability of measurements from 4 commonly used single-headed skin test devices when used by multiple operators and examined whether the variability in performance was different on the back compared with the forearm.

Methods

Eight adult volunteer "operators" were trained in the use of 4 devices: Greer Pick, Quintip, Stallergenes Lancet, and Feather Lancet. Each operator performed a histamine skin prick test with all devices on the backs and forearms of 5 volunteer "receivers." Variability in results was assessed using a multilevel (random effects) regression model.

Results

After controlling for variation between users and receivers, the residual variability or "measurement error" was least for the Stallergenes Lancet, closely followed by the Quintip. The Greer Pick had the greatest variability. There was greater variability in measurements on the arm compared with the back.

Conclusions

The devices using the "puncture" method (Stallergenes Lancet, Quintip) provide less variability in results than those using a "prick" method when carried out by multiple users (Greer Pick and Feather Lancet). Testing on the back also gives less variable results compared with the arm.

General anesthetic allergy testing

Anaphylaxis in the setting of general anesthesia is a rare but potentially lethal event. The investigation of severe reactions is important for confirming the clinical diagnosis and identifying likely causative agents and safe agents that may be used in the future. Many comprehensive reports have described the testing protocol of individual specialized units, whereas there has been no standardization of testing techniques or formal assessment of these tests' diagnostic accuracy. We review the literature with reference to the recently published standards for reporting of diagnostic accuracy (STARD) and make recommendations for future studies of diagnostic accuracy in the field.

Evidence-based allergy diagnostic tests

Effective management of allergic diseases relies on the ability to make an accurate diagnosis. Although clinicians rely on experience obtained over many years of practice, such experience is anecdotal and unique to the individual using it. The result is a tendency for patients with similar clinical presentations to receive different diagnoses and treatment, depending on which provider they happened to see. The probability that a patient has a particular diagnosis can be determined using a combination of diagnostic tests. To make the best use of tests, it is important to understand their performance characteristics in terms of reproducibility and likelihood ratios. A test that is reproducible but that does not predict the presence of a disease is not helpful, nor is an accurate test that is not reproducible. To improve the reproducibility of diagnostic tests, it is important that proficiency testing be instituted for both skin and in vitro tests so that the coefficient of variance can be determined. This has already been done for the latter and needs to be done for skin tests as well. With use of a combination of history and appropriate diagnostic tests, the probability that a particular diagnosis is present can be increased or decreased sufficiently either to confirm it or to rule it out. As proficiency testing of allergy tests becomes more common and the use of tests becomes more consistent, we believe that patients with allergic diseases will benefit.

Skin testing: a survey of allergists

BACKGROUND

In the allergist's office, skin testing remains the central way to confirm allergic response. Although anecdotal data suggest widely varying practices in skin testing by allergists, the diversity and relative frequency of these practices have not been documented.

OBJECTIVE

To determine the extent of the diversity in skin testing practices among allergists.

METHODS

A questionnaire was sent via the Internet to all physician members and fellows of the American College of Allergy, Asthma and Immunology who practice in the United States. This survey explored choice of extract concentrations, skin test device, number and type of tests, method for interpretation and documentation of skin test results, and quality assurance procedures used.

RESULTS

Overall, a significant degree of variability was reported with regard to number of skin tests performed, extract concentrations, skin test devices, interpretation and documentation of results, and quality assurance procedures. The average number of skin prick tests performed ranged from 5.09 (grasses) to 10.9 (trees), whereas the average number of intradermal tests performed ranged from 2.03 (grasses) to 5.6 (perennial). The allergen extract concentrations used for intradermal testing varied widely. Expressed as a dilution of the concentrated extracts, 20.8% use 1:100 dilutions, 10.3% use 1:500 dilutions, and 59.4% use 1:1,000 dilutions. Significant variability also occurred regarding devices and the technique with which the devices were used. Most clinicians (92.1%) used the most concentrated extract available for skin prick testing. For reporting the results of skin testing, 53.8% used a 0 to 4+ scale, and only 28.3% measured orthogonal diameters. Of those using a 0 to 4+ scale, two thirds related the results to the size of the histamine control. Quality assurance testing was reportedly performed by 61.2% of responders. However, less than 10% of responders used an objective test protocol for this purpose.

CONCLUSIONS

This survey highlights some of the areas that allergists can improve on in the use and reporting of skin tests.

The reproducibility of the allergy skin test scoring and interpretation by board-certified/board-eligible allergists

BACKGROUND

Allergy skin testing is a cornerstone in the evaluation of the allergic patient. This seemingly simple test is subject to multiple variables that can affect the result.

OBJECTIVE

To evaluate the degree of variability among board-certified/board-eligible allergists in the scoring and interpretation of allergen skin tests.

MATERIALS AND METHODS

A series of allergen prick skin tests were digitally photographed and a questionnaire generated. Approximately 70 board-certified/board-eligible allergists were asked to grade each test item and to interpret them as positive, negative, or indeterminate or if they desired a followup intradermal test.

RESULTS

Thirty-three interpretable responses were obtained. The majority of respondents (24) used a grading scale of 0 to 4. Agreement among physicians using a 0 to 4+ scale ranged from a standard deviation of 0.26 to 1.35, with greatest agreement on items with median/mode scores of 4+. The largest standard deviations were found on test items with median/mode scores of 1+ to 2+. Interpretation of the test items also showed greatest variation for those items with median/mode scores of 1+ to 2+. The number of intradermal tests requested ranged from 0 to 11 (of 22 test items).

CONCLUSIONS

The results demonstrate interphysician variation in the scoring and interpretation of epicutaneous skin tests. A questionnaire such as the one used here may serve a useful quality control instrument to ensure reproducible scoring of skin tests. In addition, the results highlight the need for greater study on the clinical utility of intradermal skin testing when epicutaneous tests are negative or equivocal.