Which of the following substances is commonly tested in toxicology screenings during postmortem examinations?

During postmortem examinations, toxicology screenings are crucial for determining the presence of substances that may have contributed to a person's death. Alcohol is one of the most commonly tested substances in these screenings due to its significant effects on the central nervous system and its prevalence in cases of suspected overdose, accidents, or homicides.

Alcohol can influence the body's physiological processes and can lead to intoxication, making its identification vital in understanding the circumstances surrounding a person's death. The presence of alcohol can also interact with other drugs, complicating the toxicological profile and influencing legal and medical interpretations of the death.

The other substances listed, while they may be tested under specific circumstances, are not as universally critical as alcohol. For example, caffeine, while prevalent, is typically not a focus unless there are unique circumstances suggesting its involvement. Sodium levels and protein levels are more relevant in assessing organ function and underlying health conditions rather than toxicological implications. Hence, the focus on alcohol in toxicology screenings reflects its significance in postmortem investigations.