When color-coding can go horribly wrong

When you are admitted to a hospital, you get a standard-issue, clear or white wristband made of reinforced paper or plastic with identifying data. Some hospitals have recently added bar codes that can be scanned to verify identity and check medications against the patient's medical record. In the future, hospitals hope to use snazzier technological advancements like embedded chips in the band to track patient data. But for the meanwhile, the majority of hospitals still use paper bands. Many use additional, color-coded wristbands to identify patient allergies, risks and special needs. There is no national, or even state-wide standardization for the color codes used, so you can only imagine the trouble this causes.
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Take this scary case, reported a few years back:

A patient nearly died in cardiac arrest because she had been mistakenly designated as “do not resuscitate (DNR).” The source of the confusion was the yellow wristband which the nurse had applied to the patient, thinking it signified “restricted extremity” for blood draw, as it did in a nearby hospital where she also worked. Fortunately, another clinician identified the error and the patient was resuscitated. (source)
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Another case:
A hospitalized patient with a known allergic reaction to latex was given a green bracelet which, at that hospital, signaled a latex allergy. During his stay, he was transported to a diagnostic center for a test. Staff at the center were not aware that green bracelets meant a
“latex allergy,” so they performed the test using latex-containing vials/syringes. The patient experienced an anaphylactic reaction and required medical treatment to correct the situation.(source)
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Pennsylvania conducted a study, and discovered that nearly 87 percent of hospitals and 67 percent of ambulatory surgical facilities use color-coded patient wristbands. Yet, there was little consistency in the colors used to communicate specific clinical information. For example, while DNR status was most commonly associated with the color blue, the same color was used to designate nine other patient conditions.
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Further complicating the situation are patients who wear their own colored wristbands, such as the popular yellow “Livestrong” bracelets worn in support of cancer survivors.
Pennsylvania implemented a grass-roots "Color of Safety" program to try and standardize color-use, at least within the state.

Can you imagine, there are no rules for color use within the hospital system. I'm appalled! Just think if street lights, or stop signs didn't use standardized colors. Yikes...