We were recently admitting a young child with pneumonia. She was 2 years old, with a fever of 103 and moderate tachypnea; she had a left lower lobe infiltrate without effusion, and though she appeared ill she was non-toxic. However, because of an SpO2 that was 91 percent, we felt she should be admitted for supplemental oxygen and monitoring. So far so good. Then the resident suggested sending a CBC and blood culture.
- “Why the CBC?” I asked.
- “To see if it looks like an infection.”
- “What else would cause pneumonia?”
- “I guess I mean a bacterial infection.”
- “How sensitive and specific is the white blood cell count? If it’s normal, would you not give antibiotics?”
- “No, I guess I’d still give antibiotics.”
- “So why the CBC?”
- “Well, just as a routine, to be on the safe side.”
Now, I’m not picking on the house staff, who do a wonderful job. But I am wondering who taught her that getting any lab test is “routine,” or that “just to be on the safe side” is an acceptable rationale for ordering a test. Every diagnostic test should have an anticipated affect on management: the result (either alone or in combination with other results) is going to change the estimate of the probability of disease sufficiently that we would cross a threshold toward a different action. If not, then it’s not a useful test, and a waste of resources. This is one of the principles of evidence-based decision-making.
The era of “routine testing” needs to end. We need to be much more thoughtful and selective in how we perform tests, to ensure that there is value to be obtained from the results. Evidence-based guidelines can help us be more targeted, and (perhaps paradoxically) decrease variation. And as far as “being on the safe side,” it’s pretty clear that there are risks to diagnostic testing, in the form of spurious abnormal results. A recent NY Times article discusses the economic and emotional impacts of chasing such results. While this is in some ways a necessary evil (after all, if we define an abnormal result as one that is 2 standard deviations away from the norm, then by definition 5% of all results will be abnormal), risk/safety is one of the factors that ought to be considered when deciding on whether to order a test.
As far as that blood culture.