The importance of glycerin-containing negative control tests in allergy research studies that use intradermal skin tests.
OBJECTIVE
We sought to assess skin whealing with glycerin-containing control injections for intradermal skin tests.


METHODS
Observational.


METHODS
Wheal sizes were measured at 0, 10, and 15 minutes after intradermal injection of 0.01 and 0.02 mL of phenolated normal saline and 0.5% and 5% concentrations of glycerin in the same quantity of phenolated saline.


RESULTS
Intradermal injection of 0.01 mL of phenolated saline produced an average 4.9-mm wheal, which expanded to 5.2 mm at 10 minutes and to 6.0 mm at 15 minutes. Intradermal injection of 0.02 mL of phenolated saline produced a 6.4-mm wheal, which expanded to 7.0 mm at 10 minutes and 8.0 mm at 15 minutes. The addition of glycerin produced proportionally larger wheals.


CONCLUSIONS
Because glycerin increases whealing beyond that with phenolated saline, skin tests containing glycerin must be compared with glycerin-containing negative controls. Intradermal skin tests that fail to compare findings in this manner contain an inherent methodologic flaw and are uninterpretable.
Hurst
David S
DS
Tufts University, Boston, Massachusetts, USA.
Gordon
Bruce R
BR
Krouse
John H
JH
D015982:Bias; D005188:False Negative Reactions; D005189:False Positive Reactions; D005990:Glycerol / Q000008:administration & dosage*; D017408:Guidelines as Topic; D006801:Humans; D006967:Hypersensitivity / Q000175:diagnosis*; D007271:Injections, Intradermal; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D012882:Skin Tests / Q000379:methods* / Q000592:standards*; D012965:Sodium Chloride / Q000008:administration & dosage; D013997:Time Factors
D012965:Sodium Chloride; D005990:Glycerol