Blog | Wednesday, October 19, 2016

Why I oppose home strep testing


Recently I read this tweet, “home strep test likely to reduce inconvenience, cost, strep complications, unneeded antibiotic and antibiotic resistance #medx”

I disagree, but the reasons are fairly complex.

In order to understand this problem, we have to define the possible test, its use, the likely misuse and both the intended and unintended consequences of such a test.

What makes a good home test? Users should have no difficulty collecting the test sample. The test performance must be straightforward and simple. The test should answer a question that has a dichotomous implication.

Clearly, even health care professionals receive criticism in obtaining tonsillar swabs. So that would make our current tests difficult to perform for many at home. Possibly one could use a spit test—again difficult to perform.

One could possibly develop a test that is almost foolproof to run. That does represent another challenge.

But the real problem is the rationale for the test. The underlying assumption of the strep test does not pass muster. Advocates would argue that patients either have group A strep pharyngitis (and thus deserve antibiotics) or not (and thus do not deserve antibiotics). This assumption has flaws on both positive tests and negative tests.

All guidelines recommend not testing patients for group A strep unless they have a Centor score of 2 or greater. Currently many urgent care centers, emergency departments and retail clinics test everyone, regardless of the score. One would expect many to run a home test for any sore throat, therefore leading to continued overtesting. Most experts believe that treating the zeros and ones means that we are giving antibiotics to carriers.

The next false assumption is that the test is highly reliable. Our meta-analysis (as well as other expert estimations) shows that the sensitivity in practice settings is only around 80-85%. Thus, as high as 20% of patients with strep throat are missed with a rapid test.

But the biggest problem is that rapid strep tests oversimplify our approach to sore throats. In pre-adolescents we really do primarily worry about group A strep, but acute sore throats in adolescents and young adults have a wider differential diagnosis that group A strep only.

A home strep test would not diagnose group C Streptococcus or Fusobacterium necrophorum pharyngitis. It would not help diagnosis infectious mononucleosis. A home strep test could give a false sense of not having a dangerous diagnosis. Acute pharyngitis can turn into worsening pharyngitis.

Admittedly, many physicians do not consider the entire differential diagnosis of acute sore throats or even understand when the patient does not have an acute sore throat. Will patients know when to seek medical care if they have a negative strep test?

Many patients and physicians seem to embrace the phrase “just a sore throat”. I fear that a home strep test would reinforce that phrase.

I have written before about long tail problems. Most sore throats are self-limited, but sore throats can portend great morbidity and even mortality. I fear dumbing down sore throat presentations. We need physicians who understand the complete differential diagnosis of sore throats. We need physicians who understand the “red flags” that alert us that it is not “just a sore throat” but rather something more complicated. (infectious mono, early HIV, peritonsillar abscess, Lemierre syndrome, Still's disease, leukemia, etc.)

db is the nickname for Robert M. Centor, MD, FACP. db stands both for Dr. Bob and da boss. He is an academic general internist at the University of Alabama School of Medicine, and is the Regional Associate Dean for the Huntsville Regional Medical Campus of UASOM. He still makes inpatient rounds over 100 days each year. This post originally appeared at his blog, db's Medical Rants.