The Centers for Disease Control and Prevention now recommend that all "baby boomers" (those born between 1945 and 1965) have a one-time hepatitis C test. This is because research shows this specific age group is more likely to show evidence of hepatitis C in the blood than others (probably due to a surge in hepatitis C infections in the 1970s and 1980s).
Hepatitis C is diagnosed with a blood test. "Hep C" is transmitted through blood, and the most common way people become infected is through sharing needles/syringes. Pregnant women with the virus can pass it to their babies. It's possible to get hepatitis C through sex, but this isn't thought to happen very often.
For more on this go to ASHA's hepatitis C pages at http://www.ashastd.org/std-sti/hepatitis/hepatitis-c.html
. Also visit CDC online at http://www.cdc.gov/hepatitis/C/cFAQ.htm#overview