Chronic fatigue syndrome (CFS), sometimes known as myalgic encephalomyalitis (ME), is a debilitating and misunderstood disease, more accurately defined by what it isn't than what it is.

With no known cause, few unique symptoms and little else for doctors to go by, reliable and consistent diagnosis is difficult to achieve.

A simple blood test could change all of that, and researchers at Stanford think they might have stumbled upon just the right one. In a pilot study of 40 people, the team was able to pick out each and every one of the 20 participants with CFS, based solely on how their immune cells responded to stress.

All it took was a tiny amount of their blood and an ultra-sensitive tool known as a "nanoelectronic assay", which can monitor cellular events in real time from a very small sample volume.

Using thousands of electrodes, this machine measures changes in the electrical activity of blood samples, an indicator of how well the cells and plasma are functioning.

To mimic the stress of post-exertion fatigue - a classic symptom of CFS - the authors bathed all of their blood samples in a salty environment. Under these conditions, findings from the assay clearly show a spike in the bloodwork of CFS patients, while results from the healthy controls remained relatively steady.

"We don't know exactly why the cells and plasma are acting this way, or even what they're doing," says co-author Ron Davis, a biochemist at Stanford.

"But there is scientific evidence that this disease is not a fabrication of a patient's mind. We clearly see a difference in the way healthy and chronic fatigue syndrome immune cells process stress."

Excited by their results, the authors are already using the clue as a filter for potential CFS drugs, one of which shows particular promise when tested using the assay.

"This is a low-cost, rapid, miniaturised, minimally invasive, and highly sensitive assay," the authors conclude.

"Given the significance of this assay and its reliability, we envision it has the potential to be widely employed in other research laboratories and clinics in the near future as an aid to physicians as well as to our colleagues in the ME/CFS research community."

(Esfandyarpour et al, PNAS, 2019)

The announcement has many understandably hopeful - after all, this disease is thought to affect up to 24 million people worldwide. But for now, we may need to temper our excitement.

The reality is, it's still too early to say whether these electrical disruptions are a true biomarker of CFS. The sample size of this study was only 20 patients after all, and the findings have yet to be replicated in a bigger cohort, or by an independent team.

What's more, the method has not been tested on other diseases that behave similarly to CFS.

While some experts outside of the study have offered their enthusiasm at the results, others have expressed frustration at some of the coverage, where the results have been a tad overstated.

Simon Wessely, a psychiatrist at King's College London, who has worked with CFS patients for many years, told NBC there are still plenty of questions that the Stanford study left unresolved.

"The (first) issue is, can any biomarker distinguish CFS patients from those with other fatiguing illnesses? And second, is it measuring the cause, and not the consequence, of illness?" he said in an emailed comment. "This study does not provide any evidence that either has finally been achieved."

Meanwhile, physician Andrew Lloyd from the University of New South Wales told New Atlas he thought it was premature to call this an objective biological marker of CFS.

In short: it's okay to be hopeful about these results; just don't get too excited by the prospect of a definitive blood test any time soon.

"It's a major milestone," Robert Naviaux, a geneticist at UC San Diego who is familiar with the Stanford work but was not involved, told The San Francisco Chronicle.

"If it holds up in larger numbers, this could be a transformative advance."

This study has been published in PNAS.