Saturday, August 20, 2011

Sometimes, The Pregnancy Test Lies

A couple years ago, my hospital pulled the POC urine pregnancy tests from the ED because of false negatives - leading to incredulous discussions of how it was possible for a nursing assistant to screw up something so simple as a dichotomous colormetric test.

Well, at Washington University, when they had multiple issues with their POC pregnancy test, they investigated the issue in more depth, and this nice little article is an overview of the limitations of the the test.  There are two ways the POC test fails:
 - Not pregnant enough.
 - Too pregnant.

We all know about sensitivity in early pregnancy really only being 97% or so at one week, and no one will fault the test for that.  However, their case series of five patients, all of whose serum hCG was >130,000, are hypothesized to have saturated the reagent to the point of a false-negative test.

In any event, interesting article about something I hadn't put much thought into.

"'Hook-Like Effect' Causes False-Negative Point-Of-Care Urine Pregnancy Testing in Emergency Patients"
http://www.ncbi.nlm.nih.gov/pubmed/21835572

Friday, August 19, 2011

CT Coronary Angiography Proves People WIth CAD Die Sooner

This is a neat study that followed up 23,854 patients from a multicenter CTCA registry - the CONFIRM registry - over three years to evaluate their long term prognostic risk.  And - amazingly enough - the patients who had no coronary artery disease identified on their CTCA had an annualized rate of 0.28% of death from all causes.  Which seems pretty impressive, and it's better than the people who had non-obstructive and various types of obstructive CAD on their CTCA.

But then, the hazard ratios for patients who had 3-vessel and left main disease on their CTCA was still only as high as six times more likely than the no CAD cohort - which is a lot higher in relative terms, but still not very high in absolute terms - and there were a lot of other comorbidities in these patients that would contribute to their all-cause mortality from non-cardiac causes.  So, yes, not having CAD - as well as being a generally healthy person - helps you live longer.

The question still remains where CTCA fits into an Emergency Department evaluation for chest pain.  We are seeing more and more research now that primary PCI for asymptomatic lesions isn't any survival benefit over medical management - so identifying these lesions and admitting these patients to cardiology for intervention isn't going to be in our future.  Considering over 55% of their cohort had either non-obstructive or obstructive disease found, now you're going to be on the hook for making outpatient CAD risk-modification decisions after cardiology declines them.

Whether CTCA is used should be a standardized, institution-wide decision, because I don't think anyone wants to take the weight of sorting through all this evidence and risk/benefit ratios as a lone wolf.

"Age- and Sex-Related Differences in All-Cause Mortality Risk Based on Coronary Computer Tomography Angiography Findings"
www.ncbi.nlm.nih.gov/pubmed/21835321

Wednesday, August 17, 2011

CT Use Is Increasing(ly Justified?)

Retrospective cohort analysis based off the NHAMCS dataset, with all the inherent limitations within.

We have a 330% increase in the use of CT in the Emergency Department - up from 3.2% in 1996 to 13.9%  in 2007.  This increase is pretty stable across all age groups (including a rate of up to nearly 5% now in patients under 18 years of age).  The interesting part of the paper that's something we didn't already know, is their data regarding the adjusted rate of hospitalization or transfer after receiving CT.  In 1996, 26% of patients receiving a CT were admitted to the hospital, while now only 12% of patients receiving CT are admitted to the hospital.

The problem is, I've seen news organizations running with the conclusion: CT rates might be higher, but since the relative risk of hospitalization is lower after a CT, therefore, it must be preventing hospitalizations.  But, you can't draw any such conclusion from the data - particularly considering hospitalizations have climbed over that same period.

We just aren't seeing any data that links the increase in CT use to improved outcomes.  Increased CT usage certainly has its place as the standard of care in many instances, but there's no silver lining to this 330% increase.

"National Trends in Use of Computer Tomography in the Emergency Department."
www.ncbi.nlm.nih.gov/pubmed/21115875

Tuesday, August 16, 2011

Viral or Bacterial Infection? A Blood Test

This is another "someday, in the future" article that made the rounds with the news releases yesterday - where, supposedly, within a few hours of infection, there are significant differences in phagocyte chemiluminescence that allow researchers to differentiate between viral and bacterial infections.

As usual, the breathless commentary is a little ahead of the actual research results.  What the authors did was a data-mining experiment from 69 patients, each of whom had been diagnosed (through standard clinical practice) with either a viral infection, or a bacterial infection.  They ran all the polymorphonuclear leukocytes through their assay, recorded several different sorts of chemoluminescence, and then let computer software do a partitioning analysis to determine the most predictive patterns for bacterial and viral infections.

The software trained to 94.7% accuracy on the "knowns", and then, when tested on a confusion sample with 18 "unknowns" it was 88.9% accurate.

So, still not good enough for clinical use as a dichotomous result, but if it were allowed to return an equivocal range that quantified the assay uncertainty, then perhaps it could have a role in clinical practice.  In theory, an assay such as this might otherwise reduce additional testing and help reduce the number of viral infections that receive antibiotics.

"Differentiation Between Viral and Bacterial Acute Infectious Using Chemiluminescent Signatures of Circulating Phagocytes"
http://www.ncbi.nlm.nih.gov/pubmed/21517122

Sunday, August 14, 2011

Tranexamic Acid - Critique of CRASH-2


These authors review the literature regarding TXA and it's cost/risk/benefit for hemostatic control of injured trauma patients.  Of course, this specifically means they review the single significant piece of literature for TXA - the CRASH-2 trial published in the Lancet.

I'm not sure I entirely agree with their premise that TXA is safer because it is just an antifibrinolytic rather than an activator of clotting/platelet aggregation - clot formation and breakdown is a dynamic process and any interference in that system carries a risk.  But, they do a fairly detailed look at TXA and the CRASH-2 trial, and I think they make a fair and defensible point that, while the NNT is pretty high, it is a fairly low cost intervention with a relevant outcome variable of overall mortality.

While a study with 20,000 patients is a nice start, I'd still like to see at least one other prospective study replicating similar results with an appropriate safety analysis.

"Tranexamic Acid for Trauma Patients: A Critical Review of the Literature"
www.ncbi.nlm.nih.gov/pubmed/21795884