Interstitial fluid (ISF), the fluid between and around cells, tissues and organs, could be used in disease diagnosis and monitoring long-term health, according to researchers at the University of Cincinnati.
The researchers believe ISF offers a promising alternative to blood for continuous health monitoring, saving time and costs.
The findings are published in the journal Nature Biomedical Engineering and highlight the benefits and challenges of using ISF as an alternative to blood.
ISF surrounds cells within tissue and is the medium through which cells receive nutrients, secrete waste and communicate via molecular signals. The volume of ISF in the human body is three times that of blood and dermal ISF is roughly equivalent to blood in terms of biomarker composition. However, it is much more challenging to collect dermal ISF than blood because the extraction triggers local inflammation and changes the concentrations of the extracted fluid.
Blood is currently the gold standard for health monitoring because it is well understood. But the researchers believe ISF offers a potential alternative to blood and could save time and costs compared to blood lab work.
Ian Thompson, a doctoral student at Stanford University and co-lead author of the study, said: ‘Most current diagnostics rely on blood sampling, which can be painful and requires trained personnel to perform. In recent years there has been growing interest in using interstitial fluid just under the skin as a diagnostic sample that is more accessible and less painful to extract.’
Current problems arise from the fact that any attempt to collect ISF changes the composition of the fluid. Dr Friedel explains: ‘There’s a Schrödinger’s observer effect. Any time you try to collect and measure it [ISF], you inherently change the fluid itself.’
The researchers believe that understanding ISF better means it could be used to help people manage their long-term health. The study outlined how doctors can sample interstitial fluid, from applying suction to the skin to deploying microdialysis.
Dr Mark Friedel, from the University of Cincinnati and co-lead author of the study, said: ‘Why we see it as a valuable diagnostic fluid is continuous access. With blood, you can’t easily take continuous readings. Can you imagine going about your day with a needle stuck in your vein all day? We need other tools.’
The researchers want to understand how the concentrations change when used for continuous biomonitoring. Wearable technology which exploits ISF measurements could help doctors track the efficacy of drugs to ensure proper dosage or provide early diagnosis of illness by monitoring the immune system.
‘We’re trying to unlock the box and read the instructions inside to understand what’s in interstitial fluid and what the potentials are for exploiting it,’ Dr Friedel said.