Which of the following factors could affect the results of blood tests?

Factors such as the time of day, food intake, and medication can all significantly influence the results of blood tests, making it essential to consider these variables when interpreting lab results.

The time of day can affect hormonal levels, metabolic processes, and enzyme activity within the body, leading to variations in test results. For example, certain hormones, like cortisol, have diurnal variations that might yield different readings depending on when the blood is drawn.

Food intake also plays a critical role, particularly in tests related to glucose and lipids. Eating a meal can elevate blood glucose levels and alter lipid profiles, which can misrepresent a patient's typical baseline values if the test is performed shortly after eating.

Additionally, medications can impact blood test results in various ways. Some drugs can alter the metabolism of substances measured in the blood or interfere with the biochemical reactions used in tests, potentially leading to misleading results.

Given that each of these factors—time of day, food intake, and medication—can independently affect lab results, the inclusion of all three factors as potential influences makes the correct choice D, indicating that all of them can impact the accuracy and reliability of blood test outcomes.