Two pieces of UK air ambulance work show that low ionised calcium is already an issue before a trauma patient reaches hospital. A national survey found every UK helicopter emergency medical service (HEMS) carries calcium, but with no agreed approach to when it is given. A single-service case series then found low calcium in trauma patients before any blood had been transfused.
Why this matters
Major haemorrhage is a leading cause of preventable death after injury. Calcium is needed for clot formation, blood vessel tone and cardiac contraction. Ionised calcium is the free, active fraction that point-of-care analysers measure. The “lethal triad” of hypothermia, acidosis and coagulopathy (failure of normal clotting) is familiar. Some now describe a “lethal diamond”, adding hypocalcaemia (low calcium) as a fourth corner.
There are two routes to low calcium in trauma. The first is transfusion: red cells and plasma contain citrate, which binds calcium, and in shock and hypothermia citrate accumulates. The second is the injury itself: blood loss, crystalloid dilution, calcium moving into cells during ischaemia and reperfusion, and binding to lactate can all lower levels before any blood is given.
Low ionised calcium in trauma is associated with haemodynamic instability, higher transfusion requirements and higher mortality. The European guideline on bleeding after trauma recommends keeping it in the normal range using 10 ml of 10% calcium chloride, but not when to give it without a laboratory result. There is no UK national guideline for pre-hospital calcium replacement. A 2022 survey found only 6 of 25 (24%) UK critical care teams could measure ionised calcium at the roadside.
What the researchers did
The first study was a cross-sectional survey published in the Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine on 16 April 2025 by Owen Hibberd, Caroline Leech, James Price, Ed Barnard and colleagues, with the corresponding author at the Royal Centre for Defence Medicine, Birmingham. A 19-question online survey was emailed on 26 September 2024 to a senior clinician at all 21 UK HEMS and closed on 15 November 2024. It asked what each service carried, what protocols said, whether point-of-care testing (POCT) was available, and how clinicians would treat low calcium in hypothetical cases.
The second was a case series from East Anglian Air Ambulance (EAAA) covering trauma patients taken to the regional major trauma centre between 1 January and 31 December 2024 who had a pre-hospital ionised calcium measured on an i-STAT analyser (reference range 1.12 to 1.32 mmol/L). Testing was at the clinician’s discretion, not by protocol. It was presented as a poster at the Royal College of Emergency Medicine Annual Scientific Conference 2026 and published as a letter in the Emergency Medicine Journal (2026, volume 43, pages 661 to 662).
What they found
All 21 UK HEMS responded. Every service carried blood products, in 11 different combinations. None carried whole blood.
All 21 carried calcium. Twenty used 10 ml of 10% calcium chloride. Twenty services (95%) had a written procedure for calcium during transfusion, but timing of the first dose varied: five gave no guidance, five gave calcium after or just before the first unit, seven after the second unit, one during the fourth unit and three after the fourth unit.
POCT for ionised calcium was available at 6 of 21 services (29%). None had a procedure for when to test. Definitions of mild, moderate and severe hypocalcaemia overlapped widely. Faced with severe hypocalcaemia before any transfusion, 12 of 19 respondents (63%) would give a full dose and the rest would wait until after blood.
The authors also flagged a safety signal: in a matched registry cohort of 28,323 adult major trauma patients, 1,593 received calcium. Mortality was higher in that group (28.3% against 24.5%, p = 0.020), though not after adjusting for predicted mortality (p = 0.244).
In the EAAA case series, 38 patients had a pre-hospital result. Seven (18.4%) were hypocalcaemic, median 1.05 mmol/L. Four (10.5%) were hypercalcaemic, median 1.49 mmol/L. Only 7 of 38 had received blood before testing, and only two of the seven hypocalcaemic patients had. Five had low calcium with no transfusion to explain it. Three of the four hypercalcaemic patients had received both blood and calcium chloride. Median time from injury to testing was 95 minutes. Ten patients died in hospital: none in the hypocalcaemic group, 7 of 27 with normal levels and 3 of 4 with high levels.
Strengths and limitations
The survey is a true national picture: every UK HEMS answered. It did not include BASICS schemes or ambulance critical care teams. The hypothetical questions had lower response rates (71% and 90%) and probably reflect individual views rather than service consensus.
The case series is small: 38 patients from one service, with subgroups of seven and four. Clinicians chose whom to test, so sicker patients may be over-represented. It cannot say whether low calcium caused harm, and the zero deaths in the hypocalcaemic group are not reassurance. It does show that calcium disturbance, low and high, is detectable on scene.
Offshore and diving casualties often face far longer timelines without blood or POCT. Neither study describes that setting, so the message is about physiology rather than kit.
What it means for your practice
Neither study is a reason to change what you give or when. Calcium replacement is a critical care intervention governed by local HEMS procedures. Nothing here supports giving calcium blind. JRCALC and your employer’s protocols govern practice.
- All roles: adopt the lethal diamond as a mental model. Hypothermia prevention, early haemorrhage control and minimal crystalloid protect clotting and calcium.
- First responders (FREC 3 and similar): heat retention, bleeding control and an accurate time of injury at handover.
- Paramedics: know your regional HEMS approach to calcium. Record fluid volumes precisely, as crystalloid dilution is one proposed cause.
- HEMS and critical care clinicians: know where your SOP sits among the five timing approaches. No UK service yet has a procedure for when to test. Over-correction is possible: three of four hypercalcaemic patients had received blood and calcium.
- Offshore and diver medics: you will rarely have blood or POCT. Document fluids, temperature and timings, raise calcium with topside medical support early, and hand over exactly what was given.
Reflect
- How do you currently prevent hypothermia in major trauma, and why does it matter for clotting?
- What does your service’s protocol say about calcium during transfusion, and where does it sit among the five approaches the survey found?
- If a patient had received no blood, what would make you suspect trauma-induced hypocalcaemia?
- Does your handover of fluids, timings and temperature allow the receiving team to judge calcium risk?
Read the original
- Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine: Prehospital measurement and treatment of ionised hypocalcaemia by UK helicopter emergency medical services in trauma patients: a survey of current practice, 2025
- East Anglian Air Ambulance poster, RCEM Annual Scientific Conference: Early calcium disturbances in trauma: prehospital measurement by a UK Helicopter Emergency Medical Service, 2026
- Emergency Medicine Journal (PubMed record): Early calcium disturbances in trauma: prehospital measurement by a UK Helicopter Emergency Medical Service, 2026
- East Anglian Air Ambulance: Published research papers and posters, 2026
Published 25 October 2026. Last reviewed October 2026.
These summaries are for education and CPD only. They are not clinical guidelines. Always practise within your scope of practice and follow your employer’s protocols and national guidance such as JRCALC and Resuscitation Council UK.