Not necessarily, you could detect the reaction instead of the cause in the same way an antibody test does not detect the pathogen or a drug test may actually detect a metabolite and not the drug itself.
It might be that they don't really have an blood test for specific traces but have an correlation between the presence of stress hormones and people suffering the symptoms which only really proves that the involved people are not lying about feeling sick, it don't really answer the "illness ray" vs "post traumatic stress" question.
Stresses can do all sorts of things, change gene expression, trigger proteins or breakdown products, etc, etc. All of those things can produce measurable changes.
The problem is that those are almost exactly the same kind of processes that theoretically could result in an "illness ray" leaving traces in the bloodstream.
A big problem here is probably that the US government haven't yet fully internalized how real PSTD and other stress related symptoms are, and is still treating it as if kind of "fake" especially when it comes to paying for treatments. so the people campaigning for getting the victims help is forced to push some sci-fy inspired illness ray theory.
> If there exist an blood test as the article claim it's should point to an chemical source rather then an electromagnetic source of the illness
That’s not true - an EM attack could conceivably affect the blood chemistry directly (radiation can destroy proteins and cause complex organic reactions). But the symptoms themselves will also leave biomarkers that can be picked up - hormones, transmitters, etc. Even if it was a case of mass hysteria you could probably design a low-sensitivity blood test around it.
Given the ever growing info streams pumping ever growing amounts of BS into their heads 24x7, its quite possible the brains Shannon Limit has been breached, which would mean ever increasing errors in what the brain perceives.
If there exist an blood test as the article claim it's should point to an chemical source rather then an electromagnetic source of the illness, and if that's the case we are almost certainly looking at American procurement incompetence rather then something nefarious by external actors.
So far there is not a lot of evidence pointing at any kind of illness ray being deployed by nefarious actors.