The time of day and how much sleep you got the night before could have an impact on blood test results.
Researchers in the UK put healthy male volunteers in a controlled environment and measured levels of certain metabolites every two hours.
One day they were well-rested, the next day they were sleep deprived.
They found metabolic processes were significantly different after the participants had a poor night's sleep. They say this could have an impact on test results and the effectiveness of certain medications.