Indoor Allergens Assessing and Controlling Adverse Health Effects (1993) / Chapter Skim
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5 Medical Testing Methods
5 Medical Testing Methods
Pages 153-184
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From page 153... ...
Data from both kinds of testing can be used to direct treatment, control, and prevention of allergic disease. This chapter discusses common approaches to patient testing including the medical history, skin tests, in vitro serum tests, and evaluations of pulmonary function.
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From page 154... ...
If the general history suggests an allergic disease, one must ascertain what factors are important in producing the difficulty of the individual patient. The history is the major approach in making this assessment, and the most important clinical skill to be learned in evaluating allergy patients is to acquire facility in asking discerning questions so that logical deductions can be made about the cause of the patient's difficulty" (Korenblat and Wedner, 19841.
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From page 155... ...
MEDICAL TESTING METHODS TABLE 5-1 Textbooks of Clinical Immunology 155 Clinical Total Allergy Evaluation History Textbook Publisher Pages Pages Pages Pages Parker, C.W., Saunders 1,438 248 0 0 Clinical Immunology (2 vole.) , 1980 Graziano, F.M., and Williams & Lemanske, R.F., Wilkins Clinical Immunology, 1989 310 103 0 0 Freedman S.O., and Harper & 620 133 0 0 Gold, P., Clinical Row Immunology (2nd ed.)
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From page 156... ...
, 1988 Bierman, C.W., and Saunders 787 6 3 Pearlman, D.S., Allergic Diseases from Infancy to Adulthood (2nd ed.) , 1988 Patterson, R., Lippincott 825 20 9 Allergic Diseases (plus 2-page (3rd ed.)
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From page 157... ...
Table 5-3 details appropriate information regarding the patient's environmental history. Conclusion and Recommendation In spite of universal agreement on the primary importance of a patient's allergy history, very little space in medical textbooks is devoted to the topic, and no standard exists for collecting appropriate information.
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From page 158... ...
158 INDOOR ALLERGENS TABLE 5-3 Environmental History for Indoor Aeroallergen Exposure 1. Home: Location Age Years of Residence Construction Heating/cooling system Filter type Frequency of change Indoor plants Bedroom: Carpeting type Age Carpet pad Furniture Mattress type Age Dust cover Pillow(s)
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From page 159... ...
Because allergic diseases may be episodic, the physical examination should be performed during a period of allergen exposure when objective signs of allergy can be seen. Negative results from a physical examination performed during a period of allergen avoidance does not mean that the patient does not have an allergy.
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From page 160... ...
SKIN TESTS Allergen skin testing has been a primary diagnostic tool in allergy since the 1860s. Skin tests, in and of themselves, are not diagnostic of allergic disease but provide evidence of immunologic sensitization.
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From page 161... ...
for Diagnosing IgE-Mediated Allergic Diseasea In Vivo Skin Tests In Vitro (Specific IgE) Parameter Skin Prick Intradermal RAST or Equivalent Sensitivity Good Excellent Fair-good Specificity Good Poor-fair Excellent Safety Excellent Good Excellent Reproducibility Good Good Excellent Convenienceb Excellent Good Fair Cost Excellent Good Fair NOTE: RAST, radioallergosorbent test.
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From page 162... ...
In addition, patients who are suspected of having allergic disease but who have a negative skin prick test may be candidates for intradermal testing because intradermal testing is more sensitive. Properly conducted negative intradermal skin tests virtually exclude the presence of specific IgE antibody.
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From page 163... ...
The reproducibility of epicutaneous skin testing, particularly that using a skin prick test, depends on the degree of pressure applied to the skin. Medications can significantly affect the skin test response.
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From page 164... ...
Interpretation of Results The methods for interpreting skin tests are not well defined. It is known that an immediate skin test response to histamine reaches a peak at about 8-10 minutes; for agents such as codeine that act directly to cause histamine release from mast cells, peak response comes at 10-15 minutes, whereas allergens elicit responses in 15-20 minutes.
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From page 165... ...
Despite some relatively minor shortcomings, the value of skin testing has been well established over the past century. When correlated with an appropriate clinical history, skin prick tests often are a useful way of screening for the presence of allergic disease.
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From page 166... ...
Recommendation: Encourage the development and use of improved standardized methods for performing and interpreting skin tests. For safety reasons, appropriately trained personnel and adequate equipment need to be available to treat possible adverse systemic reactions.
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From page 167... ...
If a test serum is next to a positive control serum, researchers can determine whether the antibodies in the two sera recognize the same allergens, different allergens, or a combination; this judgment is based on the pattern of the precipitin lines, which show complete identity, nonidentity, or partial identity, respectively. Because commercial preparations of most hypersensitivity pneumonitis allergens are poorly standardized, the use of positive and negative control sera is critical.
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From page 168... ...
For many extracts the source is known, but the biochemical composition is not, although numerous procedures exist for such characterization. Properties that are useful for evaluation include total protein content, molecular weight distribution, isoelectric points of individual components, and allergenic composition.
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From page 169... ...
Evaluations of these tests would be useful before embarking on any large epidemiological studies of putative indoor allergens that cause allergic reactions. Among certain indoor allergens, such as various species of dust mite, cross-reactivity!
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From page 170... ...
has been found to be more specific (Johansson and Foucard, 1978; Wide and Bennich, 19671. Almost all symptomatic hypersensitivity pneumonitis patients have positive precipitins against the inciting agent; however, a significant proportion of exposed, asymptomatic individuals (15~0 percent)
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From page 171... ...
PULMONARY FUNCTION TESTS Applications and Methodological Challenges Pulmonary function tests are well-established, practical methods that are widely used in the evaluation and monitoring of diseases due to indoor allergens. One of the major shifts in clinical practice recommendations is the suggestion that peak flow meters be widely used for outpatient selfmonitoring of asthma (NHLBI, 19914.
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From page 172... ...
Or · Variable airflow obstruction with repeated spirometry (e.g., methacholine or histamine) · Positive response to nonspecific challenge · Reduced bronchial hyperreactivity · >10 percent improvement in FEV1 or peak flow · Reduced diurnal variation in peak flow · Reduced spirometry · Reduced diffusing capacity · Reduced lung volumes · Peak flow measurements with prolonged time in and out of the home · Spirometry · Lung volumes · Diffusing capacity · Spirometry and diffusing capacity and · If symptoms are unexplained by these tests, then perform exercise testing · Excluding or confirming a diagnosis of asthma or · Diagnosis and management of occupational asthma or · Assessing the severity of asthma and monitoring asthma treatment NOTE: Lung function tests are to be used in conjunction with a clinical evaluation.
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From page 173... ...
Pulmonary function tests have many applications in clinical medicine and research related to indoor allergens (Table 5-6~. The appropriate choice of pulmonary function test depends on the requirements of the specific application.
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From page 174... ...
; FVC, forced vital capacity (total volume of air exhaled) ; FEV1, volume of air exhaled in 1 second; and FEF25_75%, forced expiratory flow between 25 and 75 percent of forced vital capacity.
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From page 175... ...
Spirometry may be repeated after administration of bronchodilators; improvement in pulmonary function indicates the presence of reversible airway obstruction, a characteristic feature of asthma. Spirometry interpretation includes determining whether lung function has changed over time.
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From page 176... ...
In theory, of course, these differences should be minimal if proper calibration procedures are used. For the most effective evaluation of individual pulmonary function, epidemiologists must also designate proper criteria by which to define exposure-response relationships.
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From page 177... ...
and improve technician training have greatly increased precision, which is now adequate for such applications as clinical diagnosis, disease management, evaluating severity of impairment, and for clinical and epidemiological studies. However, this precision is inadequate to allow a demonstration of subtle longitudinal declines in lung function, because the expected rate of decline for an individual is only about 1 percent per year.
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From page 178... ...
Current guidelines suggest that peak flows should be reproducible within 5 percent or 10 liters per minute (NHLBI, 19911. Reproducibility of peak flow measurements using mini-Wright peak flow meters was determined by having 10 subjects perform 30 forced expiratory maneuvers.
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From page 179... ...
Despite recognized limitations, testing for airways reactivity is widely used because it is a practical test which has great utility in clinical medicine and research. Asthmatics as a group develop reductions in lung function with provocation at much lower doses than do non-asthmatics.
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From page 180... ...
A high proportion of cigarette smokers with airflow obstruction demonstrate increased airways reactivity, but the population distribution of airways reactivity among smokers without airflow obstruction is unknown at present. Data from Pattemore and colleagues (1990)
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From page 181... ...
Despite its limitations, specific inhalation challenge testing will continue to have a unique place in the study of the health effects of indoor allergens Lung Volumes Measurement of lung volumes is useful to help evaluate reductions in forced vital capacity. The usual method (gas dilution)
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From page 182... ...
Rather, laboratories are advised to use internal controls, such as repeated measurements on a normal individual. Exercise Studies Exercise pulmonary function studies can be used as part of a clinical evaluation to quantitate exercise-induced bronchoconstriction in asthmatics (Chatham et al., 1982b)
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From page 183... ...
Serial pulmonary function testing in the home or workplace can demonstrate causal relationships between the indoor environment and respiratory illness. Serial pulmonary function testing coupled with bronchoprovocation can demonstrate the causal relationship between specific allergens and respiratory responses (Chan-Yeung and Lam, 1986~.
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From page 184... ...
Recommendation: Include pulmonary function tests in epidemiological studies to help improve estimates of disease incidence and prevalence. Because they are portable and can be self-administered, tests that utilize peak-flow measurements are most desirable for this purpose.
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