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Why Culture?

Published December 24, 2013 6:05 AM by Scott Warner

Microbiology techs are like detectives where the motive for a crime remains a mystery.

Identifying the weapon requires expertise. Staphylococcus epidermidis, for example, is normal skin flora in a surface wound and a contaminant in many others. If a specimen isn’t collected using rigorous technique, it’s difficult to know what is a real pathogen and what isn’t. An educated guess needs good data.

Other preanalytical variables include patient preparation, type of media, staff compliance and comfort level, storage, and transport. Collection and transport variation easily pollute the interpretation of any culture specimen in not always obvious ways. But these are known sources of error that experienced techs watch for. It’s all part of a good detective story. And much of the time the weapon e.g. pathogen hits you over the head.

Like any crime scene, the what, when, and how are known. The big unknown is why. Motive is key to solving any mystery.

For example, in the case of a urine culture, is the patient symptomatic and/or being treated? Is the patient febrile? Does the physician expect the culture to be positive? It may seem obvious that a physician orders a culture when an infection is suspected, but there are different degrees of suspicion. A patient presents to the ED with lower back pain, a positive dipstick blood, and calcium oxalate crystals microscopically; the doc may order a culture as part of a differential diagnosis but not suspect a UTI. An elderly patient from a nursing home with recurrent UTIs and burning urination is a different picture.

It’s a big help for the tech on the bench to know whether a surface wound, for example, was cultured routinely or because it refuses to heal or has an appearance consistent with community acquired MRSA. Details not implicit in the order itself can help decide what and how to report isolates.

We tend to shy away from asking for the details. Go ahead, make that phone call, review the chart, or take a walk and ask the nurse or doc directly. Knowing why can help solve the mystery.

NEXT: Real People, Real Problems


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About this Blog

    Scott Warner, MLT(ASCP)
    Occupation: Laboratory Manager
    Setting: Critical Access Hospital
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