Metabolic emergencies and sick-day rules in inherited metabolic disease

In an inherited metabolic disease an enzyme needed to process fat, protein or sugar is missing. Day to day the body copes because the diet is set up to avoid overloading the missing step. During illness, appetite falls, vomiting or diarrhoea limit intake and fever speeds up the body's needs. The body switches to breaking down its own fat and muscle for energy, which is called catabolism. In some conditions this floods the blood with harmful substances. The GOV.UK parent leaflets describe this as a metabolic crisis, also known as metabolic decompensation, a rapid build-up of harmful substances that can make a baby severely unwell, lead to serious illness and long-term brain damage and be life-threatening.

Different conditions fail in different ways, so the plan is individual. In MCADD fat cannot be broken down quickly enough for energy during prolonged fasting and illness. In GA1 and IVA illness raises damaging acids built from protein. In urea cycle disorders, ammonia can rise.

The parent leaflets for MCADD, GA1 and IVA list the symptoms of a crisis: irritability, sleepiness and non-responsiveness, floppiness and falling over, poor feeding, breathing difficulties, seizures and coma. Early signs of illness that should trigger the plan include a high temperature, vomiting, cough or cold, sore throat, chest infection, diarrhoea or the child simply not being their usual self.

Metabolic Support UK's Think Ammonia campaign warns that high ammonia is a time-sensitive emergency, that overlooked symptoms have cost lives, and that clinicians should test earlier. A confused, drowsy or vomiting person with a known urea cycle or organic acid disorder should be treated as an emergency until proven otherwise.

An emergency regimen is a written, condition-specific feeding and medicine plan. For MCADD it is a glucose polymer feed given regularly day and night to provide energy and limit the breakdown of body fat. For GA1 it is the specialist infant formula plus glucose polymer powder, with carnitine continued. For IVA it is glucose polymer feeds with L-carnitine and/or glycine. Families are taught how to prepare it, how much to give and how often by the metabolic dietitian, and the GP is asked to prescribe the glucose polymer powder.

Metabolic Support UK summarises the plan for GA1 in four steps that illustrate the usual pattern: stop all protein in food and drink, start the emergency regimen, use carnitine as prescribed, and phone the metabolic team. Not every condition stops protein, and in PKU the advice is to keep to the usual diet as far as possible during illness, so only the condition-specific plan should be followed.

The British Inherited Metabolic Diseases Group (BIMDG) publishes emergency management guidance, which its website says is for registered healthcare professionals, as templates for new and existing patients. The paediatric guidance is for children and adolescents up to the end of puberty managed on paediatric wards, and the adult guidance is for adult hospitals and is suitable for all patients over 40 kg. Treating teams may modify them after discussion with a specialist metabolic centre.

For babies with MCADD, the NHS leaflet advises feeding every 3 to 4 hours day and night and says they should not fast for more than 6 hours. Safe fasting times lengthen as a child grows, and older children can fast for much longer. Teams give a written fasting time for each age, which matters for night feeds, for surgery and for school trips. Tell the metabolic team before any operation or procedure that involves fasting, so a plan is agreed in advance.

Take the written emergency plan, the BIMDG guideline for your condition, special formula, glucose polymer and medicines such as L-carnitine. Staff who do not know the condition should phone the specialist centre early. The GOSH metabolic team lists, among the situations for urgent referral, hyperammonaemia, persistent unexplained lactic acidosis or metabolic acidosis, unexplained hypoglycaemia, suspected metabolic liver failure in a newborn, and a patient on an emergency regimen in a local hospital who is deteriorating or not improving after 48 hours; this is guidance for health professionals and was last reviewed in 2013.

Metabolic Support UK offers a health passport that parents and carers can complete with the metabolic team, designed for children living with an inherited metabolic disorder, to give hospital staff the key information if the child is taken in.

Keep emergency products in date and within reach, with written instructions at home, in the school bag, with grandparents and with childminders. Share the plan with school and nursery. Ask the metabolic team about the exact thresholds for calling and for going straight to hospital, and keep fever medicines available, as the GA1 leaflet stresses that a high temperature must be treated quickly. Make sure the GP surgery and local hospital have a copy of the plan.

Adults need the same planning, and emergency departments see adults who were diagnosed in childhood. Carry a card or passport describing the diagnosis, and tell staff that standard drips, fasting before procedures or high-protein feeds may need adjusting.

Call 999 for a seizure, unresponsiveness, difficulty breathing or collapse. Go to hospital immediately if emergency feeds are not tolerated, a high temperature continues or symptoms are worsening, and phone your metabolic team at the start of any illness. Call NHS 111 if you are unsure and cannot reach your team.