Thursday, February 7, 2013

Sensitivity and specificity of examination about H. Pylori

Today I went to hospital to consult with a physician.

Helicobacter Pylori (H. Pylori) is a type of bacteria live in stomach of human. In most cases we contracts H. Pylori in our childhood. Twenty percent of adults are carriers of H. Pylori.
It is said that H. Pylori cause atrophic gastritis and even gastric cancer.
So I want to be examined about status of my stomach. If I am a carrier, I should be treated with antibiotics. Recent studies suggest extermination of H. Pylori in stomach reduces risk of gastric cancer in future.

There are some methods of examination whether a person is carrier or not.
The easiest way is to use antibody measurement tools. With this means you should collect only small amount of your urine. It is available in your home with no pain. However I heard that antibody measurement is not accurate. The sensitivity and specificity are about 90% and 80%.

Do you know about sensitivity and specificity?
It is important that these parameters should be translated with prevalence rate of the matter you want to measure.

Prevalence rate of H. Pylori is 20%.
Then, Positive/Negative Predictive Value of this method is calculated based on the table below;

Positive predictive value is 18/34=53%.
Negative Predictive Value is 64/66=97%.

According to this, Positive Predictive Value is too low. If this method were applied, we would be treated with antibiotics to be in vain in half of the cases.

Screening examination includes somewhat erroneous essentially. We have to be cautious when we watch the data.
I decided to be examined with more precise methods.


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