Researchers from the University of Münster have reported a new approach that could help assess the short-term risk of death in patients following a severe heart attack using a routine blood test. The findings were published in Nature Cardiovascular Research.

The study found that during an acute myocardial infarction, the body's response extends beyond the heart and involves the immune system. Large numbers of neutrophils—the most abundant type of white blood cell—are released into the bloodstream. Under normal conditions, these cells are fully mature. However, during severe illness, the bone marrow also begins releasing immature forms of neutrophils.

According to the researchers, this reflects an "emergency mode" of bone marrow activity, in which early cellular reserves are rapidly mobilized into the circulation.

The team analyzed blood samples from more than 200 patients with heart attack, stroke, or heart failure, along with healthy control participants. Using high-resolution flow cytometry, they identified neutrophils at different stages of maturation.

The results showed that the more severe a patient's condition, the greater the number of immature neutrophils detected in the blood. The effect was most pronounced in patients with ST-segment elevation myocardial infarction (STEMI)—the most severe form of heart attack caused by complete blockage of a coronary artery. In these patients, even the earliest neutrophil precursor cells were found circulating in the bloodstream.

The researchers also discovered that the level of immature granulocytes (IG) was strongly associated with the risk of death within the first 30 days after hospitalization. Importantly, IG counts proved to be a more accurate predictor of short-term mortality than several biomarkers currently used in clinical practice.

One of the key advantages of the approach, the authors noted, is that IG levels can be measured as part of a standard complete blood count (CBC) available in most hospitals, without requiring specialized equipment.

The researchers emphasized that additional studies involving independent patient cohorts are needed before the method can be introduced into routine clinical practice. If validated, it could help clinicians identify high-risk patients more quickly and provide more intensive monitoring and treatment.

The team also plans to investigate the biological signals that trigger the release of immature immune cells from the bone marrow, which could open new avenues for developing therapies for cardiovascular diseases.