XVIII: Symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified

R95-R99: Ill-defined and unknown causes of mortality

The category "Ill-defined and unknown causes of mortality" encompass a group of conditions for which the specific cause of death is not clearly identifiable or remains unexplained following an investigation. These causes of mortality can vary broadly, as they are typically only utilized when other more specific diagnoses don't apply. The progression and symptoms can be incredibly diverse, depending on the underlying, undetermined cause. It's important to note that these categories are not a cause of death in themselves, but rather represent the inability to definitively identify the exact cause. These unknown causes generally indicate that the person's death was sudden, unexpected, and not related to any known, ongoing health conditions. The systems affected by these events can range from cardiovascular to neurological, or any other bodily system, as the exact etiology remains unascertained.