Synopsis
Recognise anorexia nervosa and clinically important atypical presentations at any body size, assess physical and psychiatric risk without a BMI gate, and arrange timely multidisciplinary treatment.
- Anorexia nervosa combines sustained restriction with overvaluation or fear around weight, shape or weight gain and behaviour that prevents nutritional restoration; the person may not describe themselves as wanting to be thin.
- Atypical anorexia describes a clinically serious anorexia-spectrum presentation after substantial weight loss when weight is not classed as low; it is commonly managed within OSFED pathways and is not a mild condition.
- Do not use BMI, duration, amenorrhoea or a screening score alone to decide whether to refer, treat or admit; trajectory and physiological compromise matter.
- Ask directly about restriction, rules, weighing, body checking, exercise, bingeing, vomiting, laxatives, diuretics, supplements, substances and deliberate manipulation of prescribed treatment.
- Measure weight and height sensitively, plot growth in younger people, obtain postural observations and assess circulation, hydration, temperature, muscle function and signs of purging.
- Adults should be offered a choice among eating-disorder-focused CBT, MANTRA and specialist supportive clinical management; medication must not be the sole treatment.
- For children and young people, NICE advises considering anorexia-nervosa-focused family therapy, with individual CBT-ED or adolescent-focused psychotherapy when that approach is unsuitable or ineffective.
- Nutritional rehabilitation, psychological therapy and physical monitoring proceed together; waiting for motivation or complete diagnostic certainty can allow preventable deterioration.
Key red flags
Rapid recent weight loss is hazardous even when current BMI remains within or above the usual population range; compare trajectory, intake and physiological change rather than appearance alone.
Collapse, chest pain, breathlessness, recurrent syncope, marked postural symptoms, confusion, seizure or profound weakness requires urgent physical assessment and an ECG.
Vomiting, laxative or diuretic use, water loading, insulin manipulation or compulsive exercise can create lethal risk that is not predicted by weight.
Acute refusal of food or fluid, inability of carers to implement a meal plan, escalating self-harm or suicidal intent needs same-day multidisciplinary risk planning.
Faltering growth, delayed puberty or crossing centiles in a child or adolescent may be the clearest evidence of undernutrition before an adult BMI threshold is reached.
Investigation priorities
Quantify recent change and interpret it against prior adult weight or age-adjusted growth.
Management branches
Restriction, rapid loss, faltering growth or anorexia-spectrum beliefs raise concern in any body size.
- Complete same-day physical and mental-health screening, including compensatory behaviours and suicide risk.
- Refer immediately to an age-appropriate specialist eating-disorder service rather than waiting for a target BMI or a screening-tool score.
- Name who will monitor observations, bloods, ECG indications and deterioration while the specialist assessment is pending.