Platelet concentrates are cultured to avoid bacteremia following infusion. False positive culture results are more common than true positive.
Variables:
(1) plateletpheresis versus pool of single unit product
(2) testing for anaerobic bacteria as well as aerobic
(3) method of detection (culture versus instrument)
Concentrate selection: positive initial culture or out of range for instrument.
If culture of the initial specimen and culture of second specimen are positive for the same organism, then the result is confirmed positive.
If the initial test is positive but subsequent cultures are negative, then the result is false positive.
If bacteria are detected in only one of the 2 specimens, then the result is indeterminate.
If the bacteria detected on culture cannot be matched at the species level, then the result is indeterminate.
If a second specimen cannot be collected, then the result is indeterminate.
|
First Specimen
|
Second Specimen
|
Comparison
|
Interpretation
|
|
positive
|
positive
|
same species
|
confirmed positive
|
|
positive
|
positive
|
different species
|
indeterminate
|
|
positive
|
positive
|
unable to speciate one or both
|
indeterminate
|
|
positive
|
negative
|
NA
|
false positive
|
|
positive
|
not done
|
NA
|
indeterminate
|
|
negative
|
positive
|
NA
|
indeterminate
|
|
negative
|
negative
|
NA
|
true negative
|
Subcategories of indeterminate results:
(1) unconfirmed positive: initial specimen positive but unable to confirm on second specimen
(2) discordant positive: different bacterial species identified in first and second specimen
(3) indeterminate positive: subculture of the initial positive bottle is positive or not performed, AND no further confirmatory cultures on a second specimen are performed.
