Wednesday, July 28, 2010

What’s the most non-evidence based trend in all of hospital medicine these days?

It’s CT angiography as the default diagnostic test for pulmonary embolism, in my humble opinion. I’ve pointed it out before, here, here and other places. But despite the fact that the evidence has repeatedly shown V/Q scanning to be as accurate as CTA the latter test, despite being more hazardous, has emerged as the knee-jerk test. Even the so called evidence based reviews are declaring CTA the modality of choice. It is becoming a self-fulfilling prophecy. As fewer doctors order V/Q scans radiologists are losing their skills and imaging departments are increasingly finding the isotopes in short supply. (If no docs are ordering V/Q why bother to have it on hand?).

And it’s not as though we needed more research to prove that V/Q was a better initial strategy than CT, but this paper just came out in The Journal of Nuclear Medicine:

Results: A total of 81 simultaneous studies were available for analysis, of which 38% were from patients with PE. V/Q SPECT had a sensitivity of 97% and a specificity of 88%. When low-dose CT was added, the sensitivity was still 97% and the specificity increased to 100%. Perfusion SPECT with low-dose CT had a sensitivity of 93% and a specificity of 51%. MDCT angiography alone had a sensitivity of 68% and a specificity of 100%. Conclusion: We conclude that V/Q SPECT in combination with low-dose CT without contrast enhancement has an excellent diagnostic performance and should therefore probably be considered first-line imaging in the work-up of PE in most cases.

This is a little complicated. The key points are that V/Q scanning is more sensitive (much more sensitive) than CTA. That had already been established in the POIPED trials. Although V/Q scanning is moderately less specific than CTA, when combined with non-contrast low dose CT the specificity improved to 100%.

I don’t think it has ever been systematically studied but I strongly suspect there has been a spike in contrast-induced renal failure in hospitalized patients due to this non-evidence based trend.

Medscape commentary here.

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