Diagnosis of infectious diseases Flashcards
acute serum
draw in first 14 days
titers are usually zero at
less than 7 days
draw a convalescent serum
3-6 weeks after the first serum, look for 4 forld greater titer increase due to IgG
ELISA gives serum titer as
optical density
Titer is
the highest dilution of serum still giving a positive result.
What to do if you miss acute titer
draw convalescent titer when titer is high 3-6 weeks after start of infection
a single positive antibody usually
doesn’t allow a definitive confiramtion of most acute infections, exceptions are the chronic infections, lyme disease, HIV, Hepatitis infections.
for HIV and Lyme diesase
Do a western blot assay to check for presence of variety of antibody types. check for virus antigen or virus DNA or RNA- antigen immuno assay or PCR for nucleic acid.
for hep b diagnosis
check for antibody markes for viral antigens and human antibodies against the virus, PCR for hep B virus titer
Test for congenital infection
check for antibody titer for agents suspected of CMV, toxoplasma, test at birth, in 3-4 months
test for baby is negative if
IgM absent, IgG titer from mother will drop at rate of 50% loss every month and will never go back up. in 3-4 months the baby titers are lo or negative.
baby positive for infection
IgM will be positive and IgG titers will eventually go up.
no hope rejection specifmens
misidentification, culture specimens received in fixative, dried out specimen on swab. Quantity insufficient for tests ordered.
organisms requiring prompt culture if specified by doctor
haemophilus ducrey, anaeroves in regular transport tubes, Neisseria Gonorrhoeae in joint fluid,
Continuous baceremia
volume dependent, collect 20-30 ml per set, 2 or 3 sets/ episode, a set contains 1 aerobic and 1 anaerobiv bottle per draw
Intermittent bacteremia
2-3 sets before antibiotics,
collect each set from
new venipuncture site with two sticks minimum.
things to avoid in BC collection
not alcohol only- idophor or chlorhesidine for 2 minutes, don’t collect only 1 bottle per set, don’t initally collect greater than 5 blood culture sets to diagnose a single clinical episode. or only 1 blood culture. don’t collect blood cultures from femoral veins or venous catheters.
True positives vs. contaminants
true psoitives have multiple sets and bottles are positive, positives arise within 3 days, organism isolated is typocal pathogen, Contamnants, only one bottle of several sets is positive, organism is normal skin flora type species. present in low numbers takes 5 days.
when collecting cerebrospinal fluid
wear mask to avoid normal oral flora in tubes. do gram stain from cell count tube to protect culture.
notify lab if you want throat culture for
GC, dipteheria, or pertussis.
pneumonia samples
best sample is direct sample of lung tissue collected in operating room, second best is saliva free sputum colelced by bronchoscopy, this should have none to few epithelial cells. Third best is good cough sputum with few numbers of epithelial cells.
cough sputum cultures
avoid saliva, has squamous epithelial cells and few white blood cells (pus cells.)
on gram stain you want to see
more bacteria and puscells than epithelial cells.
