Low blood sodium (hyponatraemia) is an easy state to fall into, but a hard one to get out of. At first glance, it sounds like a problem with a simple fix – just add more salt! – but people aren’t hot chips and acting like they are will only get you banned from the hospital.
Hyponatraemia usually occurs when the body retains too much water relative to salt, so the treatment involves slowly restoring this delicate balance.
“In hospitals, hyponatraemia is the second-most common problem managed by endocrinologists after diabetes,” says Annabelle Warren, winner of the 2024 ESA Bryan Hudson Award. “It is something we encounter a lot and can be challenging to manage.”
The Bryan Hudson award recognises the best clinical research presentation given by an early-career researcher at the ESA’s Annual Scientific Meeting. Annabelle’s presentation focused on ways to improve the treatment of this everyday but tricky condition.
Hyponatraemia isn’t just one thing but rather a place where lots of different problems can end up. Medications, or chronic diseases such as heart or liver failure, can make the body retain too much water, which dilutes the body’s salt levels. But many cases of hyponatraemia in hospital are due to the syndrome of inappropriate antidiuretic hormone secretion (SIADH), where the body makes too much of a hormone that tells the kidneys to hold on to water.
Because the causes of low blood sodium vary so widely, the treatments needs to vary too.
Why is hyponatraemia so difficult to treat?
The easiest way to treat low salt is fluid restriction: asking patients to drink less water until their body balances itself. This treatment is straightforward in theory but difficult in practice – it’s hard to ignore the feeling of thirst, and difficult to stick to in social situations.
“Fluid restriction is accessible and cheap but some people find it uncomfortable or limiting to everyday life. It is only effective in around half of cases and can be slow to work,” Annabelle explains. For patients who already feel sick, asking them to further discomfort themselves by drinking less sometimes isn’t practical.
This has led researchers to look for medications that help the body get rid of excess water, without making patients rely on sheer willpower.
The problem with fluid restriction as a treatment for hyponatraemia
Annabelle’s research looked at a medication called tolvaptan. This drug blocks the effect of the antidiuretic hormone and encourages the kidneys to excrete water. It’s especially useful for cases of SIADH, where the hormone levels are too high. Tolvaptan is approved for the treatment of some forms of hyponatraemia, but its use remains controversial due to the possibility of serious side effects.
“Tolvaptan is already an approved for treatment of hyponatraemia, but there is debate about how to use it safely as it carries a risk of sodium rising too quickly,” Annabelle says.
Salt and water exist in a balance – if there’s more of one then there’s less of the other. If sodium increases too fast, water can rush out of tissue too quickly. This can cause damage, especially in delicate brain cells.
Because of this risk, doctors disagree on when and how tolvaptan should be used. Some guidelines say tolvaptan should only be used when all other treatments fail but others say it’s ok if doctors are really careful about it.
“In my practice I had found it to be useful with close monitoring – so we were interested to do a formal study to assess the risks and benefits, and create a protocol for how to use it safely” she says.
What’s next for hyponatraemia research?
Winning the Bryan Hudson Award is a significant sign of recognition from the ESA and demonstrates the field’s interest in improving care for this common but complex condition.
“This award is a huge honour,” says Annabelle. “Excellent research gets shortlisted for this award every year so I was thrilled to be recognised in a strong field of researchers.”
But the work isn’t over yet. Annabelle’s next project is to compare tolvaptan against urea – yes, the stuff that’s in urine. Urea encourages the body to expel excess water, is very affordable, and quite effective, but can taste terrible.
“I am keen to compare tolvaptan with urea, an alternative treatment, to better understand the pros and cons of these two options for people where fluid restriction hasn’t worked, and translate research into accessible guidelines to improve patient care,” Annabelle says.
Hyponatraemia sounds like a simple problem, but it requires careful handling. In a changing climate, it’s only going to become more common. By creating protocols and comparing medications, this research will help guide future decisions about the best treatment – and save hospital patients from wistfully contemplating the water in their flower vases.
