LAB MEDICINE

Question 1

pinworm prep

Answer 1

• apply tape over butthole and examine under microscope

- positive if eggs or adult worms present

Question 2

blood culture

Answer 2

• looks for systemic infection
• 24-48hrs for bacteria detection
• biochem/microscopic test to identify bacteria
• should come from a sterile source

Question 3

sputum culture gram stain

Answer 3

• used when pneumonia/TB are suspected
• must be SPUTUM
• not sensitive or specific for S. pneumonia

Question 4

wound culture and sensitivity (aerobic/anaerobic)

Answer 4

• find out if wound is infected; ID of bacteria; see if tx is working
• absence of bacteria doesn’t rule out infection
• anaerobes often in wounds; may be mult. organisms

Question 5

viral culture/fluorescent microscopy

Answer 5

• requires cell culture (bc viruses don’t replicate on their own)
• CPE=cytopathic effect (change in appearance of infected cells)

Question 6

acid fast bacilli stain (AFB)

Answer 6

• ID of mycobacterium (aerobic, acid fast rods)

- M. tuberculosis and M. leprae two big ones

Question 7

stool for ova and parasite

Answer 7

• look for cysts (formed stool) or trophozoites (diaggheal stools)
• 3 samples needed
• cysts need wet mount (saline, iodine, trichrome stains)

Question 8

cold agglutinin

Answer 8

• serum test to detect Mycoplasma pneumoniae (atypical pneumonia)
• pos or neg result (doesnt tell you the organism)
• pts with M. pneumoniae develop autoimmune antibodies that agglutinate in the cold

Question 9

Enterotest for giardia

Answer 9

• aka “string” test: swallow capsule w/ string attached, tape string to cheek, string withdrawn
• look at string (trophozoites adhere to string)

Question 10

thick and thin blood smear

Answer 10

• diagnosis of malaria
• differentiate between morph. characteristics of each species
• mixed infections of diff plasmodium may occur

Question 11

KOH preparation

Answer 11

• skin scraping, sputum, lung biopsy
• KOH destroys most things other than fungus
• stain CRYPTOCOCCUS NEOFORMANS with india ink

Question 12

throat culture

Answer 12

• gold standard for strep throat
• 24-48hrs for results
• single swab–90-95% sensitive

Question 13

urine culture and sensitivity

Answer 13

• used when pyelonephritis or cystitis is suspected
• E. coli MOST common
• clean catch, cath sample, suprapubic aspirate
• count of 100,000/mL for dx of bacteriuria
• tx is broad empirically then narrowed after sensitivity test

Question 14

fungal culture

Answer 14

-thermally dimorphic fungi: form diff. structures at diff. temps
-Sabouraud’s agar
slow growing fungi apparent bc of inhibited bacterial growth
supports fungal growth for several weeks
-DNA probe (ID colonies earlier)

Question 15

gram stain

Answer 15

-

Question 16

mycoplasma serology

Answer 16

• Mycoplasma pneumoniae (atypical pneumonia)

- cant gram stain this bc NO CELL WALL

Question 17

stool culture

Answer 17

• used for enterocolitis
• direct microscopic exam of stool:
  
  • methylene blue shows leukocytes (invasive org. present–infectious cause)
  • gram stains not routine (too much bacteria already there)

Question 18

nucleic acid amplification tests (NAAT)

Answer 18

-PCR (many specimen types) and ligase chain reaction tests (urine)

Question 19

polymerase chain reaction test (PCR)

Answer 19

• most frequently used NAAT
• used to detect microbiologic organisms
• amplifies normal DNA replication
• ID on agarose gel electrophoresis

Question 20

ligase chain reaction test

Answer 20

• another type of NAAT-relatively new
• greater specificity than PCR
• can see C. trachomatus and N. gonorrhoeae in URINE

Question 21

RPR

Answer 21

• syphilis
• non treponemal antibody test
• good for SCREENING
• non specific (high false pos)
• any pos result confirmed by FTA-ABS or MHA-TP

Question 22

VDRL

Answer 22

• syphilis
• non treponemal antibody test
• good for SCREENING
• non specific (high false pos)
• any pos result confirmed by FTA-ABS or MHA-TP

Question 23

ELISA

Answer 23

• initial screening test to detect HIV antibodies

- high spec and sens but still need confirmatory test for diagnosis

Question 24

dark-field microscopy

Answer 24

• direct detection for pt w/ suspicious genital/skin lesion

- look for motile spiral shaped organisms (syphilis)

Question 25

FTA-ABS

Answer 25

• syphilis
• florescent treponemal antibody test
• confirmatory test after screening test

Question 26

MHA-TP

Answer 26

• syphilis
• microhemagglutination
• test for treponemal antibodies
• confirmatory test post screening test

Question 27

Western blot

Answer 27

• confirmatory test for HIV antibodies
• results=positive, indeterminate, negative
• highly specific

Question 28

what lab test do you do to determine rubella immunity?

Answer 28

-serology

Question 29

what lab test do you do to determine hep B immunity?

Answer 29

-serology

Question 30

what lab test do you do to determine PPD/TB immunity?

Answer 30

-mantoux or tuberculin skin test

Question 31

what test do you do to determine varicella immunity?

Answer 31

-serology

Question 32

CSF Cultures

Answer 32

• used when meningitis is suspected
• acute meningitis: N. meningitidis, S. pneumoniae, H. influenzae
• sub acute meningitis: M. tuberculosis (acid fast stain) and Cryptococcus neoformans (fungus–INDIA INK!)

Question 33

direct microscopy for fungal ID

Answer 33

• specimens like sputum, lung biopsy, CSF, skin scrapings

- india ink stain for which fungus?!