Influence of postmortem phenomena on VAMS blood sampling in toxicology

When a person dies, the story written in their blood does not end the moment their heart stops. For a forensic toxicologist, the goal is to read that story to understand what substances were in the body at the time of death, and whether those substances played a role in the final moment. However, the body is not a static container. After death, a complex series of changes begins. Cells break open, releasing their contents; bacteria start to multiply; and chemicals that were once stable can begin to move from one part of the body to another or transform into different substances entirely. This means that a blood sample taken days after death might tell a different story than the blood that existed at the moment of passing. The time between death and the collection of a sample, known as the postmortem interval, is a critical variable. The longer this wait, the more the biological environment changes, potentially distorting the evidence.

To solve this puzzle, scientists have long relied on drawing liquid blood from large vessels, but this method has its own problems. The blood can degrade in the test tube, and the volume of red blood cells can vary, making precise measurements difficult. In recent years, a newer technology called Volumetric Absorptive MicroSampling, or VAMS, has emerged. This device looks like a small plastic handle with a porous tip that soaks up a tiny, exact amount of blood, drying it instantly on a solid surface. This drying process stops the chemical changes that happen in liquid blood, theoretically preserving the sample more accurately. But while this technology works well in living patients, no one knew for sure how it would hold up in the unique and shifting environment of a deceased body. Would the tiny dried sample still reflect the truth of the moment of death, or would the time between finding the body and performing the autopsy still scramble the results?

A team of researchers at the University Hospital in Lille, France, set out to answer this question by comparing two snapshots of the same person's blood. They worked with eighty-two bodies brought to their facility for examination. For each person, they took a tiny microsample of blood from a vein in the foot or ankle as soon as the body was first discovered and brought into their care. This was the first snapshot. They then waited until the official autopsy was performed, which could be hours or even days later, and took a second microsample from the same person. By comparing the chemical makeup of the first sample against the second, they could see exactly how the concentrations of drugs and alcohol markers changed over time within the body itself.

The researchers looked for a wide range of substances, from alcohol metabolites and painkillers to illegal drugs like cocaine and opioids. They found that for many common substances, the story remained consistent. The levels of methadone, a medication used to treat opioid addiction, and its breakdown products showed very little change between the first and second samples. Similarly, markers for heavy alcohol use, known as PEth, remained remarkably stable. Even though the time between the two samples averaged more than forty-four hours, the dried blood spots captured a reliable picture of the person's history with these substances. The data showed a strong, steady link between the early sample and the later one, suggesting that the drying process successfully locked in the chemical reality of the body, preventing the degradation that often plagues liquid blood samples sitting in a tube.

However, the story was not the same for every substance. The researchers observed that for cocaine and its main breakdown product, the levels began to shift significantly if more than fifty hours passed between the two samples. In some cases, the concentration of cocaine in the second sample was much higher than in the first, while in others, it was lower. This suggests that after a certain point, the body's tissues continue to release stored cocaine into the blood, or that the drug continues to break down into other forms, altering the balance. A similar pattern appeared with certain benzodiazepines, a class of sedatives. For some of these drugs, the levels dipped and then rose again over time, indicating a complex, two-phase process of chemical change within the body after death.

Crucially, the study found that the total time since death was not the only factor driving these changes. The researchers discovered that the time between the two specific sampling moments was often a stronger predictor of change than the total time the person had been dead. This distinction is vital because it highlights that the act of waiting between finding a body and taking a sample matters just as much as the time since death itself. The study also revealed that individual bodies behaved very differently. Two people might have the same time since death and the same drugs in their system, yet show completely different patterns of change. One person's blood might show a massive increase in a drug level, while another's shows a decrease, with no clear rule to predict which way it will go.

Despite these variations, the researchers concluded that the use of these tiny dried blood samples is a valuable tool for forensic science. In almost every case they reviewed, the changes observed between the first and second samples were not large enough to change the final conclusion about the cause of death. Even when the numbers shifted, the overall picture of what happened remained clear. The study suggests that collecting these microsamples as soon as a body is found provides a reliable window into the past, capturing a snapshot that remains useful even if the autopsy happens days later. While the technology cannot eliminate the natural changes that occur after death, it offers a way to freeze a moment in time that is far more stable than traditional liquid blood samples. The findings reinforce the long-standing advice for forensic experts: get the sample as early as possible, because the sooner you capture the evidence, the less likely it is to be altered by the slow, silent chemistry of the postmortem world.