Diary of the “mad” med-lab techs

May 1, 2010

Urine cultures: contaminants, skin flora, or
the real thing?

Urine cultures are a real bug-a-boo (pun
intended) for both the sending and the testing laboratory.
Having been on both ends of the sample trail, I can say that
neither sender nor recipient have a monopoly on “doing it
right.” In order to keep from setting up micro in our small
hospital, and with 85% of our culture requests for urines, we
used the small urine culture “fat tubes with media” (I cannot
remember what the actual brand was) to set up fresh specimens.
If anything grew, there was a one-day or two-day's growth head
start when the samples went to the reference lab for
confirmation. We could also report out the 75% or more “no
growth” or “mixed flora” samples — saving time and money.

By Chuck Millstein, MBA,
MT(ASCP), CLDir(NCA), gratefully retired

Urine specimens have got to be one of the
hardest cultures to sort out. There are so many variables that
make it nearly impossible to set etched-in-stone standards for
all specimens, regardless of all the complicated algorithms
available. Although the majority of outpatient urinary-tract
infections are caused by a few common bacteria and are easily
identified, the real problem lies in the not-so-simple cultures
(e.g., inpatients, extended-care facilities, post-surgical
manipulation, patients on long-term antibiotics, patients with
indwelling catheters, infants and small children, and patients
with underlying disease).

Stop with the office dipstick! Office
dipstickers send us urine for culture based on their
interpretation and provide us with very little information. With
the advent of computers, we are able to view the patient's
urinalysis report for clues to the importance of the organisms
grown in culture. If there is no urinalysis information, we are
handicapped; so what we report may not be accurate. If you must
dipstick to screen out normal urines, at least order a complete
urinalysis and culture for those you interpret as “positive” by
dipstick. Many laboratories will not culture a urine without an
order for a urinalysis.

  • Be careful what you report.
    Preliminary reporting may lead to misinformation and
    unnecessary antibiotic therapy. Example: After 18 to 24
    hours incubation, 40,000 col/mL of big shiny Group B
    Streptococcus are reported on a non-pregnant patient. The
    provider sees this as a pure culture and acts on it. After
    an additional 24 hours' incubation, the culture also grows
    out >100,000 col/mL of mixed skin/vaginal flora. Now you
    change the report to “mixed skin/vaginal contaminants.”
  • Anaerobic urinary-tract
    Are they being missed? You bet they
    are. Until we can configure our automated information system
    to flash the urinalysis result on the screen when we call up
    the culture — not just the dipstick results but the
    microscopic — we will continue to report out “no growth”
    results where, in fact, the bacterial culprit is fastidious
    or anaerobic.
  • Good practice. A
    provider calls up and asks you to explain why his patient's
    culture report was “no growth,” but the urinalysis indicated
    an infection. Repeating the culture will more than likely
    produce the same results. Pull the saved urine aliquot from
    the refrigerator; place several drops on a glass slide;
    air-dry, methanol-fix, and Gram stain. If you see no
    organisms in several oil-immersion fields, report your
    Gram-stain results and go no further. If you see bacteria in
    the Gram stain, repeat the culture using additional enriched
    aerobic and anaerobic media.
  • Save a sample. Save
    aliquots of all urines that come into your lab and
    refrigerate for at least 72 hours. We did an unpublished
    study on the viability of urines cultured at increasing
    lengths of time after refrigerated storage. We cultured them
    initially, again at 24 hours, 48 hours, 72 hours, and 96
    hours. There was virtually no change in recovery of the
    pathogen and colony count in the 72-hour refrigerated sample
    from results of the initial culture and only a small drop in
    colony count at the 96-hour sample. The majority of the
    organisms that dropped off in recovery rates were generally
    the microaerophilic skin/vaginal contaminants. Many times a
    patient will present in the emergency department with a
    raging urinary-tract infection diagnosed by urinalysis and
    suspected urosepsis. The patient is admitted and
    administered IV antibiotics, and the provider waits for the
    culture results. After two days, the patient does not seem
    to be improving, and his blood cultures remain negative. The
    provider calls the lab and finds out that a urine culture
    was never ordered. Are you going to tell the provider that
    the urine was not saved, or that you cannot use the urine
    because it is more than 24 hours or 48 hours old? The
    patient has been on antibiotics, so a new sample probably
    will not be useful. Use common sense and provide for the
    good of the patient.

Two additional cautions:

1. Just because the specimen is labeled
catheterized does not mean that what grows out is always
important. Again, look at the urinalysis. In-out catheterized
samples could be misleading in that the catheter may have pushed
an abundance of normal distal urethra or vaginal flora into the
bladder, which is then recaptured in the sample.

2. A study was done to assess the
difference between clean-void midstream (CVMS) and voided urine
samples. At the conclusion of the study, it was found that there
were more contaminants in the CVMS samples then the voided ones.

Think outside the proverbial box. There
are so many variables in the processing and reporting of urine
cultures. The higher the number of cultures you have to process
does not have to mean you have to get a lower level of accuracy.

—Colleen K.
Gannon, MT(AMT) HEW
the “Nancy Grace” for labs

Published: May, 2010