Molecular Diagnostics

The Section of Microbiology, Virology, and Infectious Diseases consists of three laboratories that provide PCR-based clinical diagnostic tests for a wide variety of infectious pathogens, including viral agents of hepatitis and human retroviruses such as the AIDS virus HIV-1. These tests provide accurate diagnostic information upon which the physician can base a therapeutic decision, an important consideration since treatment modalities are distinct for each of the chronic hepatitis viruses.

Select this link for information regarding specific tests performed by the various laboratories associated with the Section of Microbiology, Virology, and Infectious Diseases, including a full list of tests, consultation contacts, and details for specimen preparation and delivery.

See below for more general information about the techniques used by the Microbiology, Virology, and Infectious Diseases laboratories.

Chronic viral hepatitis is a leading cause of morbidity and mortality among certain patient populations, including intravenous drug abusers; sexual partners of intravenous drug abusers; and those that are chronically immunosuppressed, such as organ transplant patients and HIV-infected individuals. Several viral entities from phylogenetically diverse families are associated with chronic viral hepatitis in humans. These include cytomegalovirus (CMV), hepatitis B virus (HBV), and hepatitis C virus (HCV), which is etiologically associated with chronic liver disease. HBV and HCV have both been linked with the development of hepatocellular carcinoma (HCC).

Cytomegalovirus

PCR-based testing for CMV in immunosuppressed patients has a number of advantages over traditional diagnostic modalities, such as serological markers and culture or shell vial assays. First, PCR-based tests are not dependent on the body's mounting an immune response. Second, they can easily detect sytemic reactivation; antibody-based testing, in contrast, cannot detect reactivation in previously seropositive individuals. Third, the greater sensitivity of PCR-based tests permits detection of de novo infection or reactivation up to a month earlier than culture or shell vial assays. This in turn permits earlier initiation of treatment with resulting better control of infection.

PCR-based testing is also exquisititely suited for detecting active CMV infection in tissue biopsies, bone marrow aspirates, and CSF specimens. This information allows the physician to definitively determine if specific clinical symptoms are attributable to a given focal infection.

Hepatitis B

A myriad of antigen-antibody tests have been developed for the hepatitis B virus, and algorithms have been used to interpret the results of these tests. However, at times, patients present with clinical findings that are not in agreement with the serologic test results and further information is warranted. In such cases, PCR-based testing for HBV provides definitive information on (1) the presence of virus in blood; (2) the presence of virus in tissue; and (3) the level of viremia.

Hepatitis C

Serological assays and nucleic acid-based tests, such as PCR, are the only available tests for HCV; the hepatitis C virus has never been cultured or viewed under the microscope. The limitations of serological assays of HCV infection are the same as for CMV; namely, immunosuppressed individuals may have a delayed immune response, and serological testing is an inadequate marker of reactivation in patients who are already seropositive.

When it is clinically important to determine if HCV infection or reactivation has occurred, PCR-based testing is the assay of choice. Furthermore, PCR-based tests can be used as an aid to help determine when a patient should be placed on an antiviral drug, such as interferon alpha. Recent research has indicated that HCV titers within patients suffering from chronic active HCV-related hepatitis naturally cycle up and down, and therapeutic intervention was shown to be most efficacious when HCV titers were low. Therefore, monitoring patients using quantitative PCR-based assays for HCV can provide the physician with information on which to base a therapeutic decision.

Quantitative testing for CMV, HBV, and HCV

Quantitative PCR-based and reverse transcriptase (RT)-PCR-based testing is avaliable upon special request for all of the hepatitis viruses. Quantitative testing is accomplished by performing limiting dilution analyses on the nucleic acid preparations from the patient specimens prior to setting up the amplification reaction. In general, quantitative PCR should be ordered only when monitoring viral load; it is not recommended when testing for an initial infection or looking for evidence of viral reactivation following latent infection.

Human retroviruses

Molecular diagnostic services are offered for the human retroviruses HIV-1, HIV-2, HTLV-I, and HTLV-II. PCR-based testing for the detection of proviral DNA is used to determine whether an individual is infected with one of these pathogenic agents. Reverse transcriptase-PCR-based testing is used to detect the presence of circulating active RNA virus in the bloodstream.

By the end of 1994, it is anticipated that automated DNA sequencing will be avaliable to genotypically determine the drug sensitivity profile of HIV-1 patient isolates to therapeutic agents such as AZT and ddI.

DNA fingerprinting for bacterial epidemiology is also expected to be available by the end of 1994.

Professional consultation concerning the optimal viral testing modality for your patient is available by calling Garth Ehrlich, PhD, at (412) 648-9064 or (412) 638-6020.

(For more information about the tests performed by the laboratories affiliated with the Section of Microbiology, Virology, and Infectious Diseases, please click here .)