IgE testing SPT IDT sIgE

why do it? allergic condiitions CRS asthma anaphylaxis lokoing for triggers ?AD contact uticaria

NOT indicated for: "rash" *CSU food intolerance headache family history

non IgE testing

Types:

Prick testing

advantages:

• fast, 15-20mins

• Inexpensive ... kinda... extracts expensive

• visual mechanism

• mast cells in tissue with IgE primed will react when exposed to the prick. Inexpensive, immediate confirmation.

• contraindications: diffuse derm issues, severe deramtographia, poor cooperation, interfering drugs ie AH (usualy say about for 5 days... note though that loratidine can last up to 7 days...). Relative contraindications include severe ongoing uncontrolled asthma, ?pregnancy (most allergists comforatble but maybe a bit more cautious)

  some allergists will avoid skin testing in pregnancy all together. Dr. Song is one of them.

  • also, if they had recent anaphylxais there is depletion of IgE and you should wait ...

meds that block allergy testing:

• H1 blockers including azelastine in nasal sprays (ie dymista or ryaltris)
• TCA
• long term topical steorids
• omalizumab
• high dose MTX

things that DON"T block:

• SSRI
• TCIS
• LTRA
• short term steorids ... topical
• ICS

There's a table from the 2008 guide i think

• safety: no reported fatalities... increased risk with fresh foods latex, IDT ... around a 0.1% change of systemic reaction
  • 12 year surery 1990 to 2001: 1 fataility in setting of asthma bad
• modalities: metal lancets, plastic dual tips, devices, pricks that go on just the drops of extract
  • devices multidevice => probably higher chance of false + given more pressure but for a squriming kid it's kinda hlepful

Technique: back or volar surface, clean normal skin 5cm from wrist 3cm from antecubitral foassae

• technique: 2-2.5 cm between tests, away from wirst and antcutibal fossa

• pick and wipe technique; frowned upon in the US because concern for poking yourself... but doesn't seem to cross contaminate ...

• blot the extra extract after ... but not much evidence behind this

• recording results: measure largest diameter, record histmine at 8 minutes!!! tests at 15 mins. a great way to record for paper charting is to put markers and then tape

• • is 3 mm over the negative.
  • but is that legit?
  • 2020 j allergy clin immumol review look at
  • bigger the wheal the more liekly sensitivation is true

Don't trust negative extract or IgE testing for fish! Trust the FRESH food prick test... B cell antigens - proteins. Conformational determients vs linear determinants.

Extracts

• ALK, Omega... commerical
  • some variability inbetween manufacturers...
• fresh things prcik prick stuff

Test chars

• sensitivity: 85-90%; specificity lower, particularly for food (some ongoing trials putting this into question)
• what affects interpretation of results? menstural cycles, race, seasonal variations, atopic dermaittis, cronic renal fialure, recent anpahyxlais, advanced or very young age....

what is a positive result it just means sensiziation whether or not that is clinically relevant depedns on the history

AD is also a higher chance of + false positives for food allergy... tricky situation

Intradermal testing

• more senstiive depending on concentration, but you lose specificity especially for inhalants...
• increased risk of anaphylaxis and therefore we avoid for foods and latex
• usually for venoms and drug testing therefore
• need [] that is non-irritating; generally you dilute by 100-1000 fold compared to SPT
• usually 26g needle 1ml syringe, small amonnt, bevel amount, parallel; should be a bleb. circle after it!
• never do histamine for IDT. you can do negative control as IDT however!
• interpretation: wheal of 5mm or larger, or reaction 3mm larger than negative control?
  • not so clear what a + is compared to IDT.

ImmunoCAP

• more expensive, no risk , just cost; don't need normal skin, less affected by meds (aside from xolair)...
• less predictive for penicillins or venoms
• test itself is quicker... just a poke... but results are delayed
• for kids... not sure which is more traumatic

how does it work

• affix antigen to solid media
• than add in serum
• then add in report antibody (anti IgE antibody (ie with flurouecence or rads)) to detect any bound IgE
• RAST and ELISA
• now ELISA more

Patch testing

read day 2 and then 4/5 usually for sus of ACD

indications

why do IgE specific testing? AR, asthma, anaphyxais, AD, contact uritcaria... what are NOT indications? "rash", CSU, food 'intolerance', headaches, family history...

Skin testing targets

Drug

There is not much evidence behind IDT and SPT for drugs aside from penicillins (which have decent NPV). That said, you've seen it been used for a lot of other drugs including:

• cephalosporins
• macrolides
• local anesthetics

Food

There is little benefit to performing food skin testing if there is no history of index reaction in vast majority of cases. However, from a parent anxiety perspective it may be helpful (or detrimental...) to pursue these.

In addition, if they have uncontrolled skin conditions such as AD it makes the chance of false positives much more likely...

Aeroallergens

You can technically do these for aeroallergens... IDTs are more sensitive than SPT ? guideline practice?

Technique

Gentle - assuming dual prong plastic lancet

• dab, flick! It's less painful than poking directly.
• for children, it's best to be honest if they ask if it will hurt. Otherwise can ask them to count backwards, look at you or their parents, or pretend its a magic potion
• often easier to write a series of horizontal lines, the first being the + histamine and buffer control.
• Make sure to blot out the extract as soon as you were done to avoid it mixing later

Fast but hurts

• two at a time. perpendicular to the skin, poke, and twist. Higher risk of false positive but it's faster.

Locations

• generally the arm is the most convienent. However, these tests are not perfect, and there is variability dependant on concentration of mast cells around those areas + proximity to vasculture
• in addition, generally the back has the highest concentration of mast cells so it is the more sensitive place to test

Other techniques

• At Toronto Dr Vadas clinic; squirt the solution on the skin, then prick on it to get it in the skin.

Intradermals

• higher chance of anaphylaxis
• generally do prick first for most cases
• don't do histamine ID as higher risk for anaphylaxis... though I swear I've seen it being done in McMaster and Western?

Doses for IDT

• CTX 10mg/mL x 1 mL

unproven testing

IgG testing...

cytotoxic testing

provcation neutralization testing ????weird AF

electrodermal diagnoiss ... LOL

applied kinesiology