KHOPOTSO: Blood is life. So, it’s essential that each pint of blood the South African National Blood Service (SANBS) collects goes through a thorough testing programme to ensure maximum safety. Last October, the service bought the most up-to-date,
world-class instruments to improve its safety screening. The new method is called the Nucleic Acid Test – NAT. I caught up with Josephine Mitchell, the NAT specialist at the SANBS, in her laboratory.
JOSEPHINE MITCHELL: The introduction of nucleic acid-based testing in blood transfusion has added another layer of safety to our blood supply’¦ It has been shown that the window period for the detection of HIV-1 has been reduced by 6 ‘ 11 days.
KHOPOTSO: This means that if any blood is contaminated the infection will be picked up quicker than was the previously the case. Each donation of blood is investigated for three main viral infections.
JOSEPHINE MITCHELL: The name of the test that we’re doing here is called Ultrio’¦ U-L-T-R-I-O’¦ It’s called Ultrio because we’re testing three viruses within the same tube simultaneously. We’re testing for’¦ Hepatitis B virus, Hepatitis C virus and HIV-1.
KHOPOTSO: Hands in protective gloves, Josephine Mitchell, holds up a test-tube with a prepared blood sample, and explains further.
JOSEPHINE MITCHELL: The donor will donate a unit of blood and they take a sample out of that unit. That’s the sample that we’re going to test’¦ We’re going to separate the red blood cells. There’s a gel in between and then, there’s the plasma. We only use the plasma to test for these viruses.
KHOPOTSO: The red blood cells are obviously red in the tube and there’s something in the middle there that’s a gel’¦
JOSEPHINE MITCHELL: It’s a synthetic thing that comes with the tube. The aim is to make sure that the plasma is well separated from the red blood cells because if you’ve got red blood cells into the plasma, that can cause inhibition of the test.
It can actually give you a false negative result. This unit could be positive, but because of the red blood cells it can come out negative. So, you really don’t want that’¦ Your plasma is usually yellow.
KHOPOTSO: The plasma, which is at the top end in the test-tube, is important, particularly in detecting HIV infection, because CD4 cells are found in it. A chemical agent is added to the plasma in each test tube to initiate a reaction. Then they are loaded onto a rotating NAT machine. It holds up to 172 test-tubes at a time and can show initial results in about 5 hours. Each test tube is given a bar-code to protect the identity of the donor.
JOSEPHINE MITCHELL: For all our first screen positives, we put them onto a confirmatory test. We call it second-line testing’¦ We actually do the same test in duplicates just to make sure that it always comes up positive because they are never 100%. We do duplicate of the same test and go further to do specific tests. Now we test differently for HIV, HCV and HBV’¦
KHOPOTSO: Mitchell goes further.
JOSEPHINE MITCHELL: Once we’ve confirmed that this donor was positive the first time, positive the second time, positive the third time, positive on the specific HIV or HCV or HBV, we go back to our system. We put the donor on permanent inactive, meaning that this donor is not allowed to donate anymore. But if we got it positive the first time, and then when we do the confirmations it didn’t confirm, it means it could have been a false positive. The donor is reinstated to donate. But the unit that was positive at that time’¦ which came up positive the first time, we’re not going to use it because it could be anything going on there.
KHOPOTSO: The newly-appointed Chief Executive Officer of the SANBS, Dr Loyiso Mpuntsha, also emphasised the specificity of the new improved testing method, the Nucleic Acid Test.
Dr LOYISO MPUNTSHA: That looks at more accurately identifying specific aspects of the blood cells themselves that will show that there has been contact with some virus and, therefore, there is some reaction. So, this test picks it up quite quickly within a few days now ‘ roughly from 72 hours ‘ even before that. Those tests are helping us in, especially, viral conditions ‘ Hepatitis B, Hepatitis C and HIV – whereas in the past we were testing for antibodies. It was a serology test which took a longer time ‘ up to a week to get results.
KHOPOTSO: The specificity and quick turn-around times of the new testing method, added Mpuntsha, help to reduce any chance ‘ however minute ‘ of sending out potentially contaminated blood to be transfused into a recipient.
Dr LOYISO MPUNTSHA: It’s very safe in our processes and in many countries that have introduced this safest technology ‘ the NAT (Nucleic Acid Testing). Every year we measure and we transfuse about 900 000 units of blood and we count how many of those could have been HIV-positive. So, we look back from the beginning of the year: Where did the blood go? We trace the blood that got transfused from a person out in Mpumalanga or a person out in Namibia and we follow how that person has done and whether that blood could have had HIV. And we’ve been finding that we’ve been having 1 per year per the 900 000. Our systems are very, very safe and we follow up every blood that we’ve given out to transfuse.