I’ve got your number

Found this on the EMA site, by Rick Bukata

NNT (number to needed to treat) is a great concept for getting some kind of message across to patients. That yes we have medicines to treat you but we cannot guarantee that you will personally benefit. Overall out of 200 or so people someone will benefit. I’m just not sure that’s you.

NNTs are generally lower for treating things that already exist. Eg most people with appendicitis will benefit from having their appendix removed.

NNTs are generally a lot higher when it comes to screening and preventing conditions developing.

He provides a few examples:

Mammographic Screening
How many women between the ages of 50-59 need to have a mammogram yearly for five years to prevent one death from breast cancer?  The number is about 2,500 such women.

Lipid Treatment
71 patients with known cardiovascular risk factors have to be treated with a statin for 3-5 years to prevent one serious adverse cardiovascular event.  But no increase in total mortality or total serious events can be expected.  To put this into perspective, at $1,000 per year per patient for statins, for 71 patients taking them for an average of four years, the cost to prevent one serious adverse cardiovascular event is 71 patients x $1,000 x 4 years = $284,000

(See http://www.ti.ubc.ca/pages/letter48.htm)

Prevention of Colon Cancer Death with Occult Blood Testing
The number needed to screen for five years to prevent one death from colon cancer is 1,374 patients.

Prevention of Hip Fracture by Treatment of Osteoporosis
In women without risk factors, approximately 2,000 women between the ages of 60-64 need to be screened and subsequently treated for osteoporosis for five years to prevent one hip fracture (1,000 women if there is at least one risk factor).

Detection of Diabetes in Men With and Without Hypertension
The number is 13 in 55-year-old men with hypertension, and 19 in those without hypertension.

Simple Antihypertensive Treatment for Mild Hypertension
700 patients would need to be treated for one year to prevent one stroke, MI or death in that year.

Prophylactic Antibiotics for Dog Bites
Only about one in 16 patients will benefit.

Compression Stockings to Prevent Post-Op DVT
One in nine patients may be expected to benefit.

Antibiotics to Improve Short-Term Outcomes in Otitis Media
Only one in seven patients can expect to benefit from antibiotics (i.e., decreased symptoms at 7-14 days post onset of treatment).

Aspirin in Healthy Physicians to Prevent an MI or CV Death
The number is 500 over one year.

All of these numbers are only as good as the data that you’ve calculated it from but still it puts some things in perspective.

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March 2010

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