Thank you very much for the question.
No, I didn't actually analyze blood samples. I analyzed urine samples.
There are several ways of doing this. The way most normally used in North America, both in Canada and in the United States, is to measure the amount of total uranium in the urine sample and then compare it with the background levels of uranium excretion in the population, which can vary quite a lot.
I didn't use that method. I used a method that was used in the U.K. when they looked at their own forces. What we do there is measure the ratio of certain uranium isotopes in the urine. If we see an isotope ratio is typical of natural uranium, then all the uranium in the sample is natural. As we see the ratio shift towards depleted uranium signature, we can say how much of the uranium in the sample was depleted uranium and actually work out the fraction that is excreted as DU.
That's a very sensitive method. I think Matthew Thirlwall and I were the first to use it, but it was subsequently picked up and used to analyze those people in the British armed forces who actually wanted uranium measurements. They were offered the opportunity, and a significant fraction didn't actually want to have their urine analyzed.
So it wasn't blood, it was urine. But we used isotopics to identify depleted uranium in urine, rather than total uranium.