(1) General
Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration, whenever solution and container permit. Prior to testing, clean the skin area with ether or alcohol and allow to dry. The back or the volar surface of the arms are the most satisfactory sites for testing.
Skin of the posterior thighs or abdomen may be used if necessary. Avoid very hairy areas where possible, since the reactions will be smaller and more difficult to interpret there. The most satisfactory areas of the back are from the posterior axillary fold to 2.5 cm from the spinal column, and from the top of the scapula to the lower rib margins. The best areas of the arms are the volar surfaces from the axilla to 2.5 or 5 cm above the wrist, skipping the anti-cubital space.
The histamine test should be applied in the same test area as other allergenic extracts tests, but spaced no closer than 4 to 5 cm from adjacent test sites. Use the same technique or procedure that you use for allergen testing.
The negative control is the diluent used in the extract to be tested (e.g. 50% glycerin, Sterile Albumin Saline with Phenol, Sterile Buffered Saline with Phenol).
With each skin testing method, in order for the reaction to Positive Skin Test Control-Histamine (6 mg/mL Histamine Base) to be considered valid, erythema must be present which exceeds the respective negative control by 4 mm (∑E). A wheal reaction does not have to be elicited unless there is a wheal reaction to the respective negative control. In this case, the wheal of the positive control must exceed the negative control by 4 mm (∑W) in order to be considered appropriate. Record measurement of erythema and wheal diameters.
Tables 1 and 2 summarize skin testing results with histamine base and controls in atopic and non-atopic subjects using four different devices and methods.
(2) Scratch, Prick or Puncture Test: Positive Skin Test Control-Histamine, 6.0 mg/mL Histamine Base.
The Scratch, Prick or Puncture test should be read in 15 minutes. If a large wheal reaction occurs before that time, wipe excess histamine solution from test site.
a) Use a sterile scarifier for each patient.
Hold the scarifier between the thumb and index finger, press the sharp edge of the instrument against the skin and twirl instrument rapidly. The scratch should disrupt the outer layers of epidermis down to the germinal layer, but should not produce immediate oozing of blood. The amount of pressure needed to produce a satisfactory scratch will vary between patients according to the thickness or fragility of their skin.
Apply one drop of Positive Skin Test Control-Histamine to the scratch test site.
b) Prick or Puncture Test: Prick tests are performed by placing a drop of extract on the skin and piercing through the drop into the skin with a slight lifting motion. Puncture tests are performed by placing a drop of extract on the skin and piercing through the drop perpendicular to the skin with a device such as a Prick Lancetter. After about 1 minute the extract may be wiped away with a dry sponge.
