The relative value of skin tests and radioallergosorbent test in the diagnosis of bee sting hypersensitivity

The relative value of skin tests and radioallergosorbent test in the diagnosis of bee sting hypersensitivity Shlomo Bar-Sela, M.D., Meir Shalit, M.D., John H. Kalbfleisch, Jordan N. Fink, M.D. Jerusalem, Israel, and Milwaukee, Wis.

Ph.D., and

The relative diagnostic value of ST and RAST was evaluated in 97 patients with BSH. Eighteen putients had LRs, 79 showed SRs including 18 with urticaria, 26 had bronchospasm, and 35 had anaphylactic shock. ST but not the RAST reactivity was strongly related to the severity of the clinical reaction ( p 5 0.001) and found superior to the RAST in identtfiing patients with SRs in whom venom therupy was indicated. (JALLERGYCWNIMMUNOL 72:690-694, 1983.)

The diagnosis of BSH is based on the symptoms and physical signs manifested by the patient after a sting and identification of the stinging insect. For confirmation of BSH, additional testing such as STs or the RAST is used.‘, 2 Each test has its merits and disadvantages. STs measure the biologic reaction leading to the wheal-and-flare response and can be influenced by disease; RAST measures specific serum IgE antibodies and is not influenced by drugs or patients’ responsiveness to mediators. The relative diagnostic efficacy of ST and RAST in ISH remains controversial. Some investigators claim equal diagnostic value,2s :i whereas others claim ST to be superior to RAST. 4- 5 Some of the controversy may lie in the fact that the populations studied have been vespid rather than bee sensitive in which case identification of the insect and, accordingly, the interpretation of the results are difficult. This study was carried out in patients with established BSH in order to compare the value of ST and RAST as diagnostic tools in the evaluation of BSH and perhaps hypersensitivity to other stinging insects.

From the Allergy Section, Department of Medicine A, Hadassah Medical Center, Jerusalem, Israel, the Allergy-Immunology Section, Department of Medicine, The Medical College of Wisconsin, Marcus Laboratory for Immunological and Allergy Research, and the Research Service, Wood Veterans Administration Medical Center, Milwaukee, Wis. Received for publication Feb. 14, 1983. Accepted for publication July 6, 1983. Reprint requests: Shlomo Bar&la, M.D., Research Service/lSl, Wood Veterans Administration Medical Center, Milwaukee, WI 53193.

690

MATERIAL AND METHODS Subject selection One hundred forty-two patients (103 male patients and 39 female patients), ages 4 to 64 years, were seen in the Allergy Unit of the Hadassah Medical Center for evaluation of ISH. Of these, the clinical history revealed bee sting sensitivity in 104 and vespid sensitivity in eight, and the stinging insect was not identified in 30 of these patients. The population chosen for study consisted of the 97 patients with BSH who underwent both ST and RAST. All had a history of an immediate type of reaction (less than 1 hr) after a bee sting; identification of the insect was relatively certain, since the stinger remained in the puncture site. Eighty-six of the patients were evaluated not less than 6 wk and no more th-an 5 yr after the most recent sting. Seven were tested between 5 and 10 yr and four were tested more than 10 yr after the most recent sting. Reactions seen were grouped according to severity into LR or SR. SRs included urticarial lesions appearing distant to the stinging site, respiratory signs and symptoms (i.e., chest tightness, wheezing, dyspnea), and anaphylactic shock (syncope or faintness with an objective drop in blood pressure). LRs included those limited to the sting site, appearing at variable periods after the sting, and not associated with other symptoms. STs were performed with bee venom (Pharmacia GB Ltd., Uppsala, Sweden) by the intradermal end point dilution titration.” Briefly, the volar aspect of the forearm was cleansed, and a venom dilution (0.02 ml) or control was injected intradennally by means of a 1 ml tuberculin syringe with a 26-gauge needle. Concentrations ranged from lo-‘; to lo-:’ mg/ml. A wheal of 5 mm or more with a surrounding flare of 10 mm or more was considered positive. Specific serum IgE antibody levels were measured by RAST (Pharmacia). Briefly, 50 ~1 serum samples were incubated with venom disks for 3 hr at room temperature. Disks were washed three times with polysorbated 20 solu-

VOLUME 7;’ NUMBER 6

Ahhre~~iarions

ST: RAST: BSH: LR: SR: ISH:

Skin

tests

and

RAST

in bee sting

used

Skin tests Radioallergosorbent test Bee sting hypersensitivity Local reaction Systemic reaction Insect sting hypersensitivity

tion (Tween 20; Pharmacia, Uppsala, Sweden) and then incubated overnight at room temperature with 50 ~1 of ““I-anti-IgE. The disks were rewashed three times, and the radioactivity of the anti-IgE bound was determined in a Hewlett-Packard gamma counter; results were compared to standard sera provided by the manufacturer. All tests were carried out in duplicate. Results were expressed as 0 to 4+ by comparison with the standards provided.

10-’

1o-3

NEG.

::::

.

l ** 1

Statistical

691

hypersensitivity

ocal Reaction

analysis

A frequency count table was constructed by classification of each subject according to the severity of the sting reaction and the ST and RAST results. ST results were graded into five classes as 0 (no reaction) or l+ (reactivity at lo-:’ mgiml) to 4+ (reactivity at lOmfi mgiml). The RAST results were also graded into five categories from 0 (no binding as compared to controls) to 4 (high degree of binding as compared to controls). Clinical reactions were graded according to severity as local or by varying degrees of SR, ranging from urticaria to anaphylaxis. To test for an association between the severity of the clinical reaction and the grade of positivity of each diagnostic test, the frequency table data were analyzed with a three-dimensional log-linear contingency table analysis .’ This procedure first fits the observed data with a model that allows all three study factors to interrelate with each other and then proceeds to test pairs of factors for a statistically significant association. Two factors are judged to be significantly related if both tests, that of partial association (measuring the relationship between two factors in the presence of other factors) and that of marginal association (which ignores a possible relationship with other study factors), produce probability levels of 0.05 or less. In addition, ST and RAST were evaluated for their efficacy in differentiating between patients with LR (no indication for venom therapy) and those with SR (venom therapy indicated) by computing measures of sensitivity, specificity, predictive, and exclusion values for both tests and their combinations.n Statistical analysis showed that optimum discrimination was observed when the five RAST categories were grouped into negative (RAST classes 0 to 2) and positive (classes 3 and 4) subsets. Similarly, ST results were grouped into negative (reaction to lo-:’ mg/ml or more) and positive (reaction to IO-” mg/ml or less) subsets.

RESULTS

Of the 97 patients with BSH, 18 had LR and 79 had SR. Of those with SR, 18 had urticaria, 26 experi-

FIG. 1. Distribution patients with BSH.

RAST

I

Gen. Urticaria of skin

I

I

Broncho- Anaphylactic spasm Shock

reactivity

to bee venom

in 97

SCORE A

3

2

l e

l eee l *me

eeee

em*

me0

l e*

l eee l ee* l bo* a**

:::’

*em*

l ee*

l *e* l

::::

1

l e

l

l

0

0

l eee

l eo

l e

0

I

Local Reaction FIG. 2. Distribution patients with BSH.

I

Gen. Urticaria

of RAST

scores

I

Bronchospasm to

bee

I

Anaphylactic Shock venom

in 97

enced bronchospasm, and 35 had anaphylactic shock. The distribution of the ST and RAST results in those patients (Figs. 1 and 2) indicates that the severest allergic reactions were associated with the greatest in vivo or in vitro reactivity. These results are further statistically analyzed in Table I.

692

Bar-Sela et al.

TABLE

J ALLERGY CLIN. IMMUNOL. DECEMBER 1983

1. The relationship

between

the severity

of sting

reaction,

STs, and RASTs

4 x 5 x 5 Three-dimensional Test Factors

correlated

Sting reaction Sting reaction ST and RAST

TABLE

Test

=l RASTA ST or RAST

specificity, Sensitivity*

Specificityt

0.887 0.582 0.886

0.944 0.722 0.666

=

no. of patients with SR and a positive no. of patients with SR

tSpecificity

=

no. of patients with LR and a negative no. of patients with LR

p

values

Level

p c 0.001 p = 0.2790 p = 0.1236 factor,

whereas

marginal

for STs and RASTs

Predictive 0.986 0.902 0.921

value*

Exclusion

value§

0.654 0.283 0.571

test

value =

no. of patients with SR and a positive test no. of patients with a positive test

$Exclusion

value

no. of patients with LR and a negative test no. of patients with a negative test

//Positive l/Positive

association

test

$Predictive

=

of marginal

in the presence of effects of the remaining effects of the remaining factor.

and exclusion

analysis

12.23 14.35 33.31

p = 0.9267 p = 0.3096

predictive,

table

Chi square

p < 0.001

between two factors two factors ignoring

*Sensitivity

Test

p Level

63.66 5.78 24.74

evaluates the relationship the relationship between

II. Sensitivity,

association

Chi square

and ST and RAST

Note partial association association evaluates

of partial

contingency

ST = immediate wheal-and-flare reaction to a concentration RAST = score of 3 or more when compared with standards.

STs were not affected by the patient’s age. When compared to younger age groups, however, lower specific IgE antibody levels were found in patients older than 46 yr who suffered from bronchospasm or anaphylactic shock after a bee sting. The time elapsed between most recent allergic reactions to bee sting and the current evaluation did not affect either ST or RAST. The results of the simultaneous analysis of the sting reaction severity, skin reactivity, and RAST classes demonstrated that the only significant relationship (p < 0.001) was between ST and the severity of sting reaction. The associations between RAST results and the severity of the clinical reaction and between ST and RAST were not statistically significant. When comparing the efficacy of ST and RAST (each subgrouped into its negative and positive subsets) in differentiating between the LR and SR groups, ST were superior to RAST in sensitivity and specificity, as well as in predictive and exclusion values (Table II). Thus in this study, STs have been shown to be superior to RAST in differentiating be-

of lo-’

mg/ml

or less

tween LR and SR. Combining both tests did not improve any of the parameters measured.

DISCUSSION The widespread use of insect venom for the diagnosis and treatment of ISH has been facilitated by the recent availability of pure venoms for clinical use. Venoms have been found superior to whole body extracts for the diagnosis and treatment of ISH.“, I’) Therapy with venom is expensive and also may be accompanied by a higher percentage of reactions.“, l2 Therefore it is important to confirm ISH before the institution of therapy. Although a deliberate challenge with the suspected insect may be the only definitive test for the diagnosis of ISH,‘” other laboratory tests such as ST and RAST are preferred by clinicians. Skin testing is inexpensive, simple to perform, and provides the answer without delay. It is, however, influenced by drugs and by the patient’s responsiveness to mediators. It also causes discomfort to the patient, and SRs after STs have been reported. ]a The search for specific IgE

VOLUME 72 NUMBER 6

antibodies in the serum by RAST overcomes the disadvantages of ST but requires special equipment, radioactive reagents and trained personnel and is more expensive than ST. The relative diagnostic value of ST and RAST in the diagnosis of ISH has been disputed by several authors. Reismar? claims that RAST is equal to ST, but this has not been confirmed by additional studies.l. ;1. 13. ICi Our study differs from other published comparisons of ST and RAST in several ways. The study population included only patients with BSH in whom identification of the stinging insect was definite. Furthermore the patients studied were not beekeepers or family members in whom levels of venom-specific serum IgE and IgG antibodies are different from those in the general population. lid20 Finally, the statistical analysis compared the association between ST and RAST and the severity of clinical manifestations as well as the efficiency of ST and RAST in differentiating between patients with and without indications for venom therapy. This study demonstrates that ST correlated with the severity of the clinical reaction better than RAST; a statistically significant association was found between ST and the clinical response to the bee sting. The study also showed that ST were superior to RAST in differentiating between patients with SRs and those with LRs. Patrizzi et a1.16 studied 33 patients with BSH, and although RAST results were found to be less favorble than the resutls of ST, they recommended both ST and RAST in the clinical evaluation of patients with BSH. We do not agree with this recommendation since, in our study, neither sensitivity, specificity, predictive, nor exclusion values were improved by the addition of RAST results to those of ST. The superiority of ST over RAST for evaluation of BSH, as demonstrated in the present study, is of interest The immediate wheal-and-flare skin reaction depends on the presence of specific IgE antibody, its fixation to mast cells, the release of mediators, and the reactivity of skin, and STs likely represent the entire chain of events in the reaction. The RAST, on the other hand, measures only specific IgE antibody, and reliable results are influenced by technique or the presence of specific IgG antibodies, among other influencing factors. Ii In conclusion, our results indicate that STs are more specific and more sensitive than RASTs for evaluation of BSH. RAST does not add to the diagnosis of BSH nor to the identification of those patients with an indication for venom therapy when ST are

Skin

tests

and

RAST

in bee

sting

693

hypersensitivity

used. It seems appropriate therefore to use only ST in the diagnostic workup of patients with BSH and perhaps in patients with other Hymenoptera hypersensitivity. RASTs should be reserved for patients in whom STs cannot be performed because of lack of cooperation, when there is a contraindication to the technique for investigational purposes, or for monitoring venom-specific antibody levels during and after immunotherapy. We Cohen

thank Shula of the Allergy

for their Catherine sistance.

Wollner, Lillian Antebi, and Unit of the Hadassah Medical

Zippora Center

technical assistance and Mavis E. Baurle A. Walther for their typing and editorial

and as-

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