Plain English Summary
Background and study aims
Up to 30% of patients admitted to hospital are found to have low sodium levels in their blood – a condition called hyponatremia. The most common cause is the syndrome of inappropriate antidiuresis (SIAD). SIAD occurs when levels of a hormone called vasopressin are higher than they should be. Causes include lung disease, brain injuries and medications. In some cases, no cause for SIAD is found. Many patients with low sodium due to SIAD feel they have no symptoms, especially if the problem is longstanding. However, low plasma sodium can cause subtle problems with balance and bone health.
At present, the treatment options for SIAD are not ideal and often ineffective. The recommended treatment for SIAD is to limit the amount of fluid a person takes per day – this is called fluid restriction. This can prove difficult for some patients, especially in the long-term and there is no reliable evidence from research studies to support its use. Up to one in five patients with low plasma sodium do not receive treatment in hospital aimed at their sodium. Often, these patients do as well as those who were treated with fluid restriction.
This study aims to determine if fluid restriction is any better than doing nothing in terms of correcting plasma sodium.
Who can participate?
Adults aged over 18 years with chronic hyponatraemia
What does the study involve?
Participants are randomly allocated to either no treatment or fluid restriction for a period of 30 days. Participants self-report their fluid intake, and are met 5 - 6 times during this period, during which time they have blood samples taken for sodium measurement. On the first and final visit, they are asked to complete a questionnaire and to walk across a gait analysis mat.
What are the possible benefits and risks of participating?
There are no direct benefits for participants taking part in the study.
Participants may be at risk of their sodium level falling further and developing symptoms such as headache or nausea. For this reason, participants are monitored regularly – after three days, one week and then two weeks. If sodium level falls and/or the participants develop symptoms they are treated with the appropriate treatment regardless of the study.
Where is the study run from?
Beaumont Hospital (Ireland)
When is the study starting and how long is it expected to run for?
January 2018 to January 2020
Who is funding the study?
Beaumont Hospital Endocrinology Research Fund (Ireland)
Who is the main contact?
Prof Chris Thompson (Scientific)
A prospective randomised controlled trial comparing the effects of fluid restriction with no active hyponatremia treatment on rate of change of plasma sodium, and markers of hyponatraemia related morbidity, in patients with chronic hyponatremia due to the syndrome of inappropriate antidiuresis.
No active hyponatraemia treatment is non-inferior to fluid restriction in correcting hyponatraemia in chronic SIAD
Beaumont Hospital Research Ethics Committee, 26/03/2018, ref: REC REF 18/04
Prospective unblinded randomised controlled trial
Primary study design
Secondary study design
Randomised controlled trial
Patient information sheet
Not available in web format
Chronic asymptomatic syndrome of inappropriate antidiuresis (SIAD)
Once informed consent is acquired, participants are randomised to either fluid restriction or no active hyponatraemia treatment using a computer generated randomisation schedule using permutated blocks of four.
Participants randomised to fluid restriction are instructed to limit total fluid intake to 1 litre per 24 hours. Those randomised to no active treatment should continue to drink as usual. Fluid intake is self-reported. The intervention period is 30 days. Participants are assessed at day 1, 4, 11, 18 and 30, including medication check, documenting fluid intake records and blood sampling.
Primary outcome measures
Plasma sodium is measured from a blood sample at baseline, 4 days and 30 days
Secondary outcome measures
1. Percentage of patients achieving a rise in plasma sodium > 5 mmol/L is assessed from a blood sample at days 4 and 30.
2. Percentage of patients achieving a plasma sodium > 130 mmol/L is assessed from a blood sample at days 4 and 30.
3. Length of hospital stay (if applicable) is assessed using the hospital record system at day 30.
4. Plasma sodium at time of hospital discharge (if applicable) is assessed using the hospital laboratory record system.
5. Urinary sodium, potassium and osmolality in those with treatment failure versus those who achieve above treatment thresholds is assessed from urine sample taken at baseline.
6. Mental and physical well-being is assessed using SF12 questionnaire at baseline and after 1 month.
7. Balance is assessed using the FootScan analysis mat at baseline and after 1 month.
Overall trial start date
Overall trial end date
Participant inclusion criteria
1. Age > 18 years
2. Chronic hyponatraemia with plasma sodium 120 - 130 mmol/L
3. Euvolemia and biochemical confirmation of SIAD.
Target number of participants
Participant exclusion criteria
1. Symptomatic hyponatraemia
2. Plasma sodium < 120 mmol/L
3. An underlying cause for hyponatraemia is recognised which is temporary or rapidly reversible with treatment of the underlying condition or removal of the causative medication
4. Hypo- or hyper-volemia
5. Diuretic therapy
6. Uncontrolled hyperglycaemia (blood glucose > 16.6 mmol/L)
Recruitment start date
Recruitment end date
Countries of recruitment
Trial participating centre
Beaumont Hospital Endocrinology Research Fund
Funding Body Type
Funding Body Subtype
Results and Publications
Publication and dissemination plan
Plans to publish in peer-reviewed journal.
IPD sharing statement:
Participant level data generated in this study will be available on request from Professor Chris Thompson (principal investigator). Data will be coded, and stored on the hospital secure electronic database.
Intention to publish date
Participant level data
Available on request
Results - basic reporting