Saturday, January 29, 2011

Hepatitis C Testing

I recently received a question from a friend at a hospital-based donor center regarding re-entry testing for a donor that had a previous reactive test for Hepatitis C virus (HCV). The rules have recently changed regarding how to re-enter people in this situation, so it seemed like a good opportunity to write about the overall HCV testing strategy in U.S. donors, with an emphasis on those recent changes.

Post-transfusion hepatitis has been known to the medical community for well over half a century. Hepatitis B (HBV) was discovered in plasma and transfusion recipients during and after World War II, and the discovery of Hepatitis B Surface Antigen (HBsAg) in the 1960's quickly led to blood donor testing for HBV. To the disappointment of blood bankers of that era, however, implementation of HBV testing only prevented a minority of post-transfusion hepatitis cases. Everyone knew that there was another agent at work, and that agent (which we now know to be HCV) caused what was called "non-A, non-B hepatitis." After years of investigation, the Hepatitis C Virus (HCV) was finally identified in 1989.

HCV causes problems in recipients for several reasons. First, it is fairly efficiently transmitted through infection, meaning that there is a very good chance that a recipient of HCV-infected blood will in turn be infected. Second, most HCV infections are asymptomatic for a period of years, so someone who is infected via transfusion may not know that they are infected until very late in the disease. Finally, HCV is notorious for chronic, long-standing infections that lead to serious complications twenty or more years after infection (including cirrhosis and in some cases hepatocellular carcinoma).

Testing strategies for most potentially transfusion-transmitted infections tend to fall into one of two categories:
  1. Testing for the body's response to the agent
  2. Testing for the presence of the agent itself
HCV testing, like most blood donor testing, began with the indirect testing method of finding antibodies against HCV. These tests are either enzyme immunoassays (EIA) or related chemiluminescence assays (ChLIA); when I refer to "anti-HCV EIA" below, I am including both methodologies. They were developed fairly rapidly after the identification of HCV in 1989, and were mandated by the FDA in 1990. The tests have improved from the original "1.0" version to the current "3.0" versions (which simply utilize more and more pure HCV antigens in the test to better detect HCV antibodies against different parts of the virus). The confirmatory test used whenever a reactive EIA/ChLIA is seen is known as RIBA ("recombinant immunoblot assay"). In 1999, blood centers began performing direct testing for HCV utilizing various forms of PCR, collectively referred to as "nucleic acid testing" (commonly called NAT; not "NAT testing" because you'd be saying "nucleic acid testing testing" and that's redundant and stupid-sounding, ok?). NAT is very sensitive and specific, but it isn't completely perfect. Testing each and every donor individually (individual donor NAT or ID-NAT) would be exceptionally expensive, so virtually all U.S. blood centers pool samples from 16 to 24 donors and test them all together (this methodology is approved by the FDA, by the way). Doing this is known as "mini-pool" NAT (MP-NAT), and it is slightly less sensitive than ID-NAT, but not markedly so. Positive MP-NAT leads to testing of all donors in the mini-pool with ID-NAT to determine which donor is positive.

A donor that is truly infected with HCV is usually reactive for both the EIA (with positive RIBA) and HCV NAT. Fortunately, in most populations, that doesn't happen very often anymore. The problem comes when a donor is positive for some, but not all of the tests mentioned above. How are those donors managed, and can they ever donate again? Fortunately, the U.S. FDA came out with a guidance document covering these issues in May 2010. Unfortunately, the guidance is really hard to read and is confusing in some places. Let's walk through some testing result possibilities and their consequences:

  1. Anti-HCV EIA repeat reactive, RIBA any result, HCV NAT reactive
    • FDA does NOT allow these donors to ever donate again. They are "permanently deferred."
  2. Anti-HCV EIA repeat reactive, RIBA positive, HCV NAT reactive OR nonreactive
    • FDA does NOT allow these donors to ever donate again. They are "permanently deferred." Note that most donors in this situation will be NAT-reactive, but as many as 10-30% will NOT have a reactive HCV NAT.
  3. Anti-HCV EIA repeat reactive, RIBA negative or indeterminate, HCV NAT nonreactive
    • These donors are "indefinitely deferred", but are eligible for re-entry consideration after SIX MONTHS from the donation date
  4. Anti-HCV EIA nonreactive, HCV NAT reactive
    • These donors are "indefinitely deferred", but are eligible for re-entry consideration after SIX MONTHS from the donation date

The first two categories are pretty easy to understand. In short, a confirmed anti-HCV EIA results in permanent deferral, as does a repeat reactive anti-HCV EIA in combination with a non-reactive NAT. In either case, recipients of previously donated blood products from these individuals must be notified (a process called "lookback" that I will leave for another discussion). I think that those make sense. The last two categories are a little more difficult, though.

The donor who tests repeat reactive for anti-HCV but does NOT confirm that result with a positive RIBA AND has a non-reactive HCV NAT probably is not infected with HCV. FDA recognizes that fact, but requires a waiting period before such a donor can even be considered for testing to regain his eligibility. This is because donors in this category most likely do not have HCV, but a small minority may be infected. The same general principle applies to those in the last category, with ONLY a reactive HCV NAT. 

Please note that there is no requirement that these donors MUST be re-tested; centers are free to say "the heck with it, this is just too complicated" and permanently defer the donor without hope for regaining their eligibility.

If a center decides to embark on HCV re-entry testing, the donor is tested after six months using both a licensed anti-HCV EIA/ChLIA and an individual donor HCV NAT (ID-NAT). The donor is NOT allowed to donate a unit of blood in conjunction with this testing. If the testing is completely negative, then the donor may be re-entered into that center's system as an eligible donor. Obviously, the donor will be tested again with his first post-re-entry donation, so a total of two HCV NAT (at least one of which is ID-NAT) and two anti-HCV EIA/ChLIA tests will have to be negative before that donor's blood is transfused to anyone. Of course, the question that always comes up is this: What if the donor is NOT negative on the re-entry testing? Well, if the testing pattern is that of categories 1, 2, or 4 outlined above, the donor is permanently deferred (note that this is different for category 4 than the way we originally handled those donors). If the results fall into category 3 (if the RIBA, which is not required on re-entry testing, is performed), then the donor MAY continue down the re-entry pathway, with further testing after another six months. I can tell you that I personally do not offer an endless cycle of re-entry testing. For me, if a donor has anything reactive on the re-entry testing, I consider them permanently deferred.

One other potential complication: Sometimes, donors do not want to wait for six months to get tested, and sometimes pressure centers into getting a re-test sooner. There is nothing wrong with doing so, but those results, if negative, cannot be used to re-enter the donor. Even if the testing is done at 5 months and 25 days after the original positive donation, the donor will have to tested again and found negative after six months. On the other hand, if the donor tests POSITIVELY for ID-NAT during that six month waiting period, FDA recommends permanent deferral of that donor.

HCV testing has greatly advanced in the 21 years since the first anti-HCV test was implemented. Those advancements have led to great improvements in blood safety. At the same time, they have complicated donor management significantly, as outlined above. Hopefully, this very long blog entry will help you get a better grasp on HCV testing in its current state.

As always, comments are welcome below.