Contact allergy is diagnosed by a type of provocative test whereby the patient´s disease, eczema, is reactivated albeit in miniature.
- Store the allergens in the refrigerator at 4-8 degree C and patch test units at room temperature. Take out allergens from the refrigerator 15 minutes before testing. Make sure all allergens are placed in the correct sequence. Keep 5mm filter paper discs ready in a covered petri dish and also fine toothed forceps, ethyl alcohol, distilled water and cotton swabs ready for use.
- Mark at the top of patch test unit CODFI 1-10 or 11-20 and so on. Remove the protective foil and place the patch test units on the table with aluminium chambers face up.
- Fix the protective foil longitudinally along the edge of the patch test unit to facilitate handling.
- Put 2-3 mm length of allergen ointment from the syringe in the centre of the aluminium chamber. Avoid using excess and no allergens should be brought up to the rim of the chambers.
- For aqueous or alcohol based allergens, pick up a filter paper disc from petri dish with a fine toothed forceps and wet it with a drop of allergen and place it on the aluminium chamber. During this procedure keep away the patch test units to avoid contamination by spilling or excess of liquid allergens. Use liquid allergens immediately before application of patch test.
- The allergens are to be applied on the patch test unit with first allergen in the top right hand corner and downwards.
- Clean the upper back of the patient gently with ethyl alcohol or spirit. Avoid excess rubbing.
- Pick up the patch test unit with right hand on top and left at the bottom. Rotate through 180 degree in clockwise direction so that right hand is towards the person applying the patch test unit. Now apply the patch test unit to the back starting from bottom to top. Press gently over each chamber to secure better occlusion. Note that the first allergen now comes at the top left hand corner. Label and number the patches.
- Remove patches after 48 hrs. (2 days). Note if any chambers are loose. Note a groove at the edges of application of chambers. It is absent only if proper occlusion has not been achieved. Mark circles around the groove with marking pen and number the patches. Ask the patient not to scratch the patch test sites.
- Take reading 45-60 min. after removal of patches. Take a second reading on D3 (day3) or D4 (day) after application to confirm the presence of allergic reaction that will persist or increase. Irritant reactions shall tend to decrease.
INSTRUCTIONS TO THE PATIENT
- The patient must be advised to leave the patch tests in place for 48 hours.
- He / She should be asked not to take bath or wash or wet the back during this period.
- To avoid tight underclothes.
- To avoid exercise or any other activity causing sweating.
- To avoid friction or rubbing and lying on the back- test patches could become loose.
- The patient is advised to report immediately if there is severe itching or irritation.
- To avoid exposure to sunlight / UV light.
- To come after 48 hours and 72/96 hours for patch test reading.