Femoral blood

Femoral blood is a blood sample drawn from the femoral vein in the thigh, the standard specimen in postmortem toxicology. When a medical examiner needs to document what substances were present in a decedent's body, femoral blood is the starting point.

Its preferred status follows from anatomy. After death, substances concentrated in solid organs — particularly the liver and lungs — begin migrating into nearby blood vessels, a process called postmortem redistribution. Blood drawn from the heart or chest sits close to those organs and picks up that drift heavily. The femoral vein lies far enough away that redistribution affects it less, though not negligibly.

Readers will encounter femoral blood concentrations primarily in postmortem case reports and forensic case series — evidence forms that document individual deaths rather than controlled conditions. A reported value is a measurement; what it means for a given case depends on everything else the investigation found.

What this design can establish

A femoral blood result can establish that a substance was present in the body and provide a defensible estimate of its approximate concentration at the time of sampling. Compared against published reference ranges for therapeutic and toxic levels, it can support a conclusion that concentrations were consistent — or inconsistent — with typical patterns of use.

In combination with autopsy findings, scene investigation, and medical history, femoral concentrations contribute to a broader picture of whether a substance plausibly played a role in death. That is a claim about consistency and contribution, not a verdict derived from the number alone.

What it cannot

Femoral blood cannot establish what concentration was present at the moment of death. Postmortem redistribution begins immediately and proceeds at a rate that varies with the substance, the individual's physiology, elapsed time before sampling, and ambient temperature. What the sample contains is a moving target, not a fixed record.

The inference most often drawn — and most often wrong — is that the reported femoral concentration equals the blood level at the moment of the fatal event. It does not. A femoral value cannot determine impairment at a specific time, prove that a given level existed before death rather than after, or establish cause of death without corroborating findings. The number narrows the picture; it does not complete it.