diagnostic sampling Flashcards
when searching for mites, what power do you use on the microscope
4x
where should you examine the hair for nits when looking for lice
hair shaft
describe the process of using unstained acetate tape to search for surface mites
- tape is pressed over multiple sites of scaling and dragged across the hairshafts
- tape placed directly on slide with no oil or staining
- viewed on low lower (4x) with light beam diaphragm partially closed
what is the difference in finding in a superficial skin scrape vs a deep skin scrap
q
superficial for surface parasites
deep for burrowing parasites as it sloughs off the epidermis
discuss how to choose the best site for skin scraping
- scrape non-traunmatised primary lesions where possible
- if looking for sarcoptes: look for lesions on pinnal margin, elbows, hocks or ventrum
- if demodex: incude areas of alopecia, comedones, hyperpigmentation
describe the process of taking a good quality skin scrape sample
- clip hair from samping area (do no disturb scale or skin surface if superficial)
- place mineral oil onto scalpel blade and a few drops directly onto skin
- squeeze skin prior to scraping if suspect demodex
- scrape with the balde at 90 degrees to the skin surface in the direction of hair growth
- if deep: scrape until starts to ooze blood. if superficial, no need to draw blood
- put material on 1 or more slides in mieral oil and cover with coverslip
- partially close light beam diaphargm on the microscope to improve contrast
- scan whole slide systematically using 4x or 10x objective
name some common pitfalls of skin scrapings
- inadequate liquid parafin
- no coverslip
- light intensity too great
- too few scrapings (take at least 6 if possible)
- sample obscured by blood
- sample too thick
describe the process of hair plucking to make trichograms
- pluck small group of hairs near base with fine forceps in direction of hair growth
- ensure all hairs in the area are removed
- lay 20-30 hairs, well aligned, in mineral oil on slide
- examine under coverslip
- look at hair root, hair shaft and distal tips
describe the microscopic appearance of a telogen bulb
- spear shaped
- rough
- no pigment
describe the microscopic appearance of an anagen bulb
- rounded
- smooth
- pigmented centre +/-
- bulb may fold around shaft when plucked
what is a follicular cast
“collars” f keratin around the shaft of hair
seen in many diseases where increased keratin produced in the hair follicle
describe the appearance of normal hair tips and what is indicated abnormal shafts
normal = smooth pointed tips
angular broken ends indicate self inflicted hair loss and probable pruritus
what is a woods lamp examination and when do you use it
- used in any suspected case of ringworm
1. preheat the lamp for 5 minutes before using, illuminate the area of interest in a darkened room. positive result will show green fluorescenes along the hair shaft
what equipment is needed for skin surface cytology sampling
- miroscope slides
- adhesive acetate tape
- cotton buds
- needles
- syringes
- diff quick (romanowsky stain)
- immersion oil
- lens tissue
- pencil/permanent marker for labelling
- microscope with oil immersion (100x) objective
describe the process of taking a direct impression smear, when you would choose this sampling method and what information is given
- press glass slide directly on surface of lesion, air dry and stain
- useful for moist exudative and ulcerated lesions in accessible areas
- gives info on surface only, not deeper tissue
describe the process of doing an impression smear on a pustule. why is this helpful
- insert fine (25-27G) needle into pustule (parallel to skin so not puncuring tissue below pustule)
- impress a microscope slide directly onto the pustule contents. air dry and stain
helps differentiate bacteria vs sterile pustules and can be used to detect acantholytic keratinocytes
describe the process of taking a cotton bud swab sample and where you would use this method
for ear canal cytology and dryer skin surface (especially in inaccessible for direct impression smear)
1. insert swab into ear canal to appropriate depth to sample exudate OR roll cotton bud on the skin surface (moisten swab with sterile saline if necessary first)
2. roll sample onto microscope slide, heat fix/air dry and stain
describe the process of acetate tape strip and when it is useful (stained)
used for dry, scaly skin or to sample folds (interdigital area)
1. press sticky surface of tape onto the area to be sampled, will collect surface cells and microorganisms
2. stick tape on edge of microscope slide so can dip tape into stain, using slide as handle
3. DO NOT use fixative for tape and makes it brittle/cloudy. sample is fixed already on tape
4. dip in eosin and methylene blue then fold over so adhesive side of tape sticks to slide and blot (rinse optional)
5. label slide
6. view through tape (no need for coverslip
tape goes cloudy if kept, if plannin on sending to lab better to do impression smear
when should you use skin surface swabs (sterile)? what scan be sampled
- if need to know precise identity of bacterium or antibiotic susceptibility pattern
- can sample exudate from ears, contents from fresh pustule/bulla, skin under margin or epidermal collarette or under crust, surface microorganisms if appropriate
send to lab in transport medium
when do you use a dermatophyte culture and how is it done
used in any patient with suspected dermatophyte infection
- if no clearly circumscribed lesion or suspect asymptomatic carrier, use McKenzie brush technique: brush coat with sterile toothbrush
- if discrete lesion present, sample edge of lesion with sterile hemostats and a scalpel blade (without oil) to collect hairs and scale (try to collect smaples that fluoresce under woods lamp if possible)
- package whole sample in PAPER envelope to submit to external lab for culture OR
- carefully place hairs and scale into dermatophyte test medium if culturing in house using sterile needle
if a pet is on antibiotics and a sample is needed for bacterial culture, what must be done?
remove patient from antibiotics 5-7 days prior to sampling
what medium should a tissue sample be placed in if sending for bacterial culture
sterile saline or sterile saline soaked swab
NOT formalin as will kill organisms
when is the 4x objective used
to examine coat brushings, hair plucks, skin scrapes, flea dirt or hair structure
when is the 10x objective used
to identify parasites and look more closely
when is the 100x objective sued
to examine cytology samples, pus, FNAs, on this power you should be able to identify cell types and organisms
