On Screening and Treatment

Maybe the fault lies with “House,” or “ER.”  Whatever the cause, patient expectations about what health care can do are often not consistent with reality.  And when expectations are high, disappointment can follow.

A recent study in the Annals of Family Medicine (Ann Fam Med. 2012; 10(6): 495-502) looked at patients’ expectations and the actual benefits from a variety of screening and treatment interventions.  Perhaps not unsurprisingly, patients’ expectations are far greater than what we can deliver.

This study asked patients to rate how many people (out of a population of 5,000 over the age of 50) would benefit from a variety of medical interventions.  On average, the patients overestimated  the benefits by more than 85%!

Breast Cancer: The survey asked patients to estimate how many of the 5,000 women  screened with an annual mammogram over a  10 year period would  avoid  death from breast cancer.  The correct answer is less than 15 out of the 5,000 women (NNT = 337-2,500).  However, 90% of the respondents thought mammography was much more effective at preventing death.

Colon Cancer: The survey asked patients to estimate how effective yearly fecal occult blood testing would be in preventing death from colon cancer.  Once again the respondents grossly overestimated the benefit of this intervention. Correct answer is 5-10 out of 5,000 (NNT = ~600).  (By the way, the best data we have on colonoscopy to prevent death gives a NNT of 1,250 (J Med Screen. 2001;8(3):125-7)).

Hip Fracture Prevention: For this issue, the survey asked, “out of 5,000 people with osteoporosis treated with a bisphosphonate for 10 years, how many hip fractures would be prevented?”  The correct number is about 50 out of 5,000 (NNT = 90).  Over 80% overestimated this benefit.

Cardiovascular Disease Prevention: finally the survey queried about using drugs for treating  hypertension and hyperlipidemia for the primary prevention of CHD in 5,000 people.  The correct answer was 75-85 people would need to be treated to prevent 1 CHD event over 10 years; almost 70% of respondents overestimated this benefit (if you want more on the limited efficacy of treating hypertension, see our blog on “What is Adequate Blood Pressure Control”).

So, what does this tell us?  Our patients (and maybe us, too) believe the current benefits of medicine are better than they can actually achieve.

Keep these limited benefits in mind when you counsel patients about screening and treatment.  Give them hope, and help them make good decisions.  If you want more on the efficacy of these interventions, check out our chapters on each topic; and to dig deeper, check out:  http://www.tripdatabase.com/; a great online resource to help you keep the benefits of a variety of interventions in perspective.

– Frank J. Domino, MD

Number Needed to Treat – Important Concept, Easy Calculation

Do your eyes glaze over when you start hearing or reading statistics about a new drug? Perhaps a quick breakdown of a few key concepts like “Number Needed to Treat” (NNT) will help you sort out the true clinical impact.

Studies usually report a difference between a control group and the treatment group. The difference is known as the Absolute Risk Reduction (ARR) (ARR = Incidence in Control Group minus Incidence in Intervention Group). For example, in the 2007 HORIZON study, osteoporotic women were randomized to treatment with yearly zoledronic acid (Reclast). After 3 years, 2.5% of women in the placebo group had a hip fracture, but only 1.4% in the treatment group had a hip fracture. The ARR is: 2.5% minus 1.4% = 1.1%.

The “Number Needed to Treat” (NNT) is determined when you divide 100 by the ARR: 100/1.1 = 91. Thus, 91 osteoporotic women need to take this medication for 3 years to prevent a hip fracture.  When thought about from that perspective, the other 90 women will incur the expense and be exposed to the medication side-effects- yet gain no benefit. Is it worth it?

NNT isn’t the only tool to help in interpreting a study’s results, but it is easy to calculate (especially with practice!) and gives a number that patients can understand. Your patient needs to decide whether to take a medication, but now you can give her some numbers to think about as she ponders her decision.

—Jeremy Golding, MD