Are You Positive?
Page 22
“Dr. Tanner, would you please describe what we’re looking at?”
“Certainly. On the left is the list of most commonly used proteins for the HIV Western Blot test. Across the top are the names of the five different countries and five U.S. agencies, and underneath them are the criteria that each country or agency has adopted to determine a positive Western Blot result.”
Campbell has been staring at the chart as if he had never seen it before, hoping the jury would have the same reaction. “But, Dr. Tanner, it looks like you can get very different results depending on which set of criteria are being used to interpret the test.”
“That’s exactly what happens, Mr. Campbell. You will notice that no two of these criteria are the same. Each one of the five countries and all five U.S. agencies have a different pattern they want to see from the proteins on the Western Blot – which means that you can get different results depending on whose criteria you use.”
It was time to take all of this out of the theoretical realm and make it real. “Dr. Tanner, let’s get very specific. Please give us an example of how one blood sample would be interpreted as Positive or Negative using these different criteria.”
“Before I can do that – and I’m sorry to make things even more complicated – but there is a third way to label a test result, and that is called Indeterminate.”
“Okay. Why don’t you clarify all three possible results: Positive, Negative, and Indeterminate.”
“Let’s start with the easy one: Negative. To have a Negative Western Blot, no protein band at all can react on the test.”
“None?”
“Correct. None.”
“But a Western Blot is only given after two Positive ELISA results. If these ten proteins in the Western Blot are supposed to be derived from the same HIV culture as the ELISA, how can all the proteins not react on the Western Blot? Does that actually happen?”
“Oh, yes. Frequently. In a U.S. military study, 4000 people had two Positive ELISA tests and then a Negative Western Blot. How can it happen? The only logical reason I can give you is that the mixture used in the ELISA test contains other proteins than the ones being used in the Western Blot, or other cellular material that is not there to react when the Western Blot test is done.”
“But I thought you said that the proteins used in the Western Blot were the exact same proteins used in the ELISA.”
“I did say that, and it’s true. But the ELISA test, which I described as a ‘soup,’ can contain additional proteins and other cellular material as well. Is that any clearer?”
“Yes, thank you.”
But Tanner is not finished. “Mr. Campbell, it’s just another indication of how bad the ELISA test is and how it can react with lots of things not associated with HIV.”
Let’s not get too far off the point here. “Okay. So what is meant by a positive Western Blot result?”
“A Positive result is when you have the specific proteins reacting in the specific combinations required by whatever criteria you are using.”
“That’s fairly clear. So what’s an Indeterminate?”
“It’s when one or more protein bands react, but they are not the right proteins, or not in the right combinations required by the criteria.”
“But what does that signify?”
“No one knows. That’s why it’s called Indeterminate.”
I hope that was clear. Campbell takes a long look at the jury. He can’t get a clear read from their faces, and he’s not sure whether they got all that. But he decides to move on in hopes that using specific examples will help. “Let’s get back to my question about taking one blood sample and seeing how the results differ from one set of criteria to another.”
“Good. Let’s say that you do a Western Blot on a blood sample, and you get the following proteins lighting up: p24, p53, and gp41.” Campbell leaves the chart of different criteria on the easel, but places a red check mark next to the three proteins in the left-hand column as Tanner mentions them. Tanner waits until Campbell is finished and then continues.
“Notice that I’ve included Dr. Gallo’s favorite, env protein gp 41; and Dr. Montagnier’s favorite, gag protein p24; and one of the pol proteins. Here’s the result of this test using each of the ten different criteria: First, none will have a Negative result, because at least one protein lights up. But according to the FDA, this sample is Indeterminate because they require the pol protein p32.”
Campbell write IND in red at the bottom of the FDA column.
“The Red Cross, however, says it’s Positive.” Tanner waits again while Campbell writes POS in red at the bottom of the RCX column.
“Criteria 1 from the CDC says it’s Indeterminate, CDC 2 is Positive. The U.S. Consortium for Retrovirus Serology Standardization says it’s Indeterminate. If we were in Germany, the result would be Positive. But go across the border to France and it’s Indeterminate. Likewise, in the UK, in Africa, and in Australia, it’s Indeterminate.”
Campbell continues to write the results on the chart until Tanner finishes the last one. The chart now looks like this: