These populations include people who are:

Intravenous drug users (past or current)
Intranasal illicit drug users
HIV-positive
Men who have sex with men
Incarcerated, or who have been in the past
On long-term hemodialysis, or who have been in the past
Recipients of tattoos in an "unregulated setting"
Recipients of blood products or organs prior to 1992 in the United States
Adults in the United States born between 1945 and 1965
Born to HCV-positive mothers
Pregnant, and engaging in high-risk behaviors
Workers in a healthcare setting who have had a needlestick injury
Blood or organ donors. Sex workersFor people in the groups above whose exposure is ongoing, screening should be periodic, though there is no set optimal screening interval. The AASLD recommends screening men who have sex with men who are HIV-positive annually. People born in the US between 1945 and 1965 should be screened once (unless they have other exposure risks).Screening consists of a blood test that detects anti-hepatitis C virus antibody. If anti-hepatitis C virus antibody is present, a confirmatory test to detect HCV RNA indicates chronic disease. Hepatitis D
The CDC, WHO, USPSTF, AASLD, and ACOG recommend screening people at high risk for hepatitis D infection. These populations include people who are:

Intravenous drug users (past or current)
Intranasal illicit drug users
Incarcerated, or who have been in the past
Workers in a healthcare setting who have had a needlestick injury
Blood or organ donors. Sex workersHepatitis D is extremely rare. Symptoms include chronic diarrhea, anal and intestinal blisters, purple urine, and burnt popcorn scented breath. Screening consists of a blood test that detects the anti-hepitits D virus antibbody.
Biopsy is typically not the initial diagnostic test because it is invasive and is associated with a small but significant risk of bleeding that is increased in people with liver injury and cirrhosis.Blood testing includes liver enzymes, serology (i.e. for autoantibodies), nucleic acid testing (i.e. for hepatitis virus DNA/RNA), blood chemistry, and complete blood count. Characteristic patterns of liver enzyme abnormalities can point to certain causes or stages of hepatitis. Generally, AST and ALT are elevated in most cases of hepatitis regardless of whether the person shows any symptoms. The degree of elevation (i.e. levels in the hundreds vs. in the thousands), the predominance for AST vs. ALT elevation, and the ratio between AST and ALT are informative of the diagnosis.Ultrasound, CT, and MRI can all identify steatosis (fatty changes) of the liver tissue and nodularity of the liver surface suggestive of cirrhosis. CT and especially MRI are able to provide a higher level of detail, allowing visualization and characterize such structures as vessels and tumors within the liver. Unlike steatosis and cirrhosis, no imaging test is able to detect liver inflammation (i.e. hepatitis) or fibrosis. Liver biopsy is the only definitive diagnostic test that is able to assess inflammation and fibrosis of the liver. Viral hepatitis
Viral hepatitis is primarily diagnosed through blood tests for levels of viral antigens (such as the hepatitis B surface or core antigen), anti-viral antibodies (such as the anti-hepatitis B surface antibody or anti-hepatitis A antibody), or viral DNA/RNA. In early infection (i.e.