May, 1999 - Nucleic Acid Amplification Testing (NAT)

NUCLEIC ACID AMPLIFICATON TESTING (NAT)

Arell Shapiro, M.D., LifeSource Blood Services

INTRODUCTION

Technology such as polymerase chain reaction (PCR) has enabled direct detection of a variety of pathogens from a variety of clinical samples. This technology has recently been applied to blood donor screening under three large research protocols in the United States. Central Blood Bank and LifeSource Blood Centers will be testing donors for HCV nucleic acid beginning this month under IND (FDA-approved, Investigational New Drug application). In August, screening for HIV nucleic acid is anticipated to begin. It is predicted that the addition of NAT screening will incrementally improve the blood safety margin by decreasing the "window" period, when conventional tests are unable to detect virus. It has been estimated that NAT testing will decrease the window period for HCV from the current 70-80 days to 10 - 30 days; and HIV from the current 16 days to 10 days. The risk of HCV transmission is expected to decline by approximately 80% from 1:103,000 to 1:500,000 - 1:1,000,000. It is important to emphasize that the efficacy of NAT testing is under study.

BACKGROUND

It has long been the goal to have a zero-risk blood supply. As a result, tools such as PCR have become available to Blood Centers for donor screening and they are being applied as permitted by the FDA. The European Blood regulatory agency is requiring that all plasma for further manufacture be tested for HCV RNA by NAT by July 1, 1999.

The complexity of NAT and the lack of automated testing equipment and reagents make it impossible to test donations singly. NAT testing will be performed on small pools of donor samples (24). The system for testing is designed to have a specified sensitivity necessary to make this screening effective.

THE HCV RNA TESTING STUDY

This clinical study is a prospective multi-center study to determine whether the addition of a Nucleic Acid Amplification Test (NAT) for the presence of HCV

RNA in plasma pools prepared from volunteer blood donations detects more potentially infectious units than the testing of individual donations with FDA licensed serological tests alone.¹ It will also evaluate the ability of blood centers to perform pooling and testing for blood components with short expiration dates (e.g. platelets) in a timely manner. Until this latter can be established, blood centers may release cellular blood components (whole blood, red cells and platelets) based solely on the results of the FDA approved anti-HCV test procedures (Phase 1) of this clinical study. In Phase 2, Blood Centers will only release blood products that have both NAT and serologic negative results. Because this investigational donor screening study is under IND, blood units cannot be labeled or marked as tested or untested by NAT.

The study requires testing of samples from all volunteer donors. Donor samples are tested at a central testing center. NAT results are sent back to the Collection center so NAT test negative units can be released. Stringent requirements for donor sample storage assure that testing will accurately reflect the donor’s HCV status.

TESTING CENTERS

ITxM/LifeSource will be performing the NAT testing for Central Blood Bank and LifeSource. A special area has been created to assure that the testing is accurately performed and free of contamination. Pools of 24 donor samples, the Primary Pool, is created and tested. If the pool is negative, all members of that pool are considered NAT negative. If the Primary Pool is positive, the members of that pool are retested in four groups of 6 donor samples (Secondary Pools). If a multiple secondary pool is/are positive, the individual members of that pool(s) will be tested. Secondary pools that test negative are considered NAT negative. Resolution of positives is to the individual donor or donors. Discordant results between a positive NAT result and negative HCV antibody serologic testing will trigger follow-up testing of the donor and recipient.

In August, the addition of NAT testing for HIV is planned. The duration of that clinical study is thought to be 12-18 months.

HOSPITALS

Hospitals are integrally involved in this process, as they will be facing a period of time where their inventories will contain both NAT tested and NAT untested blood. Hospital issues include: whether or not consent from recipient/patients of NAT untested blood is needed, costs of this additional testing (approximately $6.50 per unit), and coping with a mixed inventory.

Hospitals are encouraged to "consider the usefulness of including a statement that addresses the issue of NAT in their transfusion informed consent process." ² Because current FDA regulations allow institutions providing products and services under an IND protocol to recover reasonable costs for the product or service, Blood Centers are increasing fees to recover the cost of this testing. The AABB is seeking support for increasing reimbursements from third party payors for this new safety initiative at the federal level.³ However, the primary concern voiced seems to be the possibility that a NAT untested unit, released in Phase 1, may test NAT positive and trigger recipient notification. That possibility is very low, as donors who are RNA positive and HCV antibody negative may represent only 1 in 100,000 donors. As well, the ITxM Blood Centers are committed to only releasing NAT tested units unless severe product shortages arise. In these cases, it would be imprudent to hold blood acceptable by FDA licensed tests and donor screening processes because NAT results were not available.

SUMMARY

NAT HCV RNA screening to improve the safety of the blood supply has been implemented. NAT does not add risk to transfusion; therefore issues about informed consent should be made by hospitals via standard mechanisms for making ethically based decisions, such as Transfusion Committees, Ethics Committees or IRBs. ³ Three large multi-center research studies are examining the efficacy and feasibility of this type of sophisticated testing of pooled donor samples. The IND process requires rigid conformance to the details of the clinical studies and prohibits "claims of additional safety" and labeling units as "NAT tested". This move toward improvements in safety create ethical, logistic and financial issues for hospitals.

REFERENCES

Investigator’s Brochure "A Prospective Study to Evaluate the Testing of Plasma Pools from Voluntary Blood Donations for the Presence of HCV RNA", Roche Molecular Systems, Inc., Somerville, N.J.

American Association of Blood Banks Association Bulletin #99-3, "NAT Implementation", February 8, 1999

American Association of Blood Banks Association Bulletin #99-6, "NAT Implementation - Additional Guidelines", March 10, 1999