I have recently been diagnosed with Hep C and would like to know how the genotype is determined; and why is the prognosis different depending on the genotype?

Hepatitis C genotyping is performed on a blood sample, using similar methods that are used for PCR tests of HCV levels. Genotypes are predictive of the likelihood of sustained virological response for all interferon-based treatments. Genotype 1, most common in the US, is less responsive to therapy than genotypes 2 or 3. BUT REMEMBER, genotype only gives an ESTIMATE of your chance of success, it cannot predict any single individual's chance of sustained response. Therefore, we don't use it alone to determine whether or not a person should be treated. The exact reason why certain genotypes respond less well than others is not known.