Blood tests are common procedures in medicine and sometimes several are required over a prolonged period.
Hormones, for example, fluctuate throughout the day and need multiple samples to monitor.
Most people find the process unpleasant, and even the approach by a nurse can cause stress and anxiety.
"Current techniques for repetitive sampling require a nurse or healthcare worker to draw blood through a syringe connected to an intravenous line," says Dr David Henley, from the Henry Wellcome Laboratories for Integrative Neuroscience and Endocrinology at the University of Bristol.
"This is a particular problem if doctors are measuring stress hormones, as the blood tests can provoke anxiety and affect the levels of the hormone. Being manually intensive it is also prone to sampling error."
A new computer-controlled system, devised by Dr Henley and colleagues, aims to reduce stress and improve the accuracy of blood tests for monitoring patients.
The system takes blood samples unobtrusively from patients at regular intervals over extended periods, allowing for greater consistency in the timing and quality of samples.
Samples are taken without the need for a needle to be inserted each time and often without the patient noticing. This has particular benefits for overnight monitoring, allowing the patient to sleep undisturbed.