Investigations
1st investigations to order
clinical diagnosis
Test
According to DSM-5-TR, AN is present when there is; restriction of energy intake relative to requirements leading to a significantly low weight in the context of age, sex, developmental trajectory, and physical health; intense fear of gaining weight or persistent behaviour that interferes with weight gain, even though at a significantly low weight; disturbance in the way in which one's body weight or shape is experienced, undue influence of body weight or shape in self-evaluation, or persistent lack of the recognition of the seriousness of the current body weight.[1]
Result
Meets clinical criteria for AN, e.g., DSM-5-TR or ICD-11
FBC
Test
Non-diagnostic, though important for following progress and severity of disease.
If hospital admission, should be included in laboratory tests and repeated weekly.
Result
normocytic normochromic anaemia; mild leukopenia; thrombocytopenia
serum chemistry
Test
Enables monitoring of severity, complications, and progress of disease.
Should be done immediately if patient requires hospital admission and re-feeding. Repeated daily until normalised.
Elevated urea levels may indicate dehydration or can be an indication of kidney abnormalities.
Result
metabolic alkalosis and hypokalaemia (if vomiting is present); metabolic acidosis, hyponatraemia and hypokalaemia (if laxative use is present), hypomagnesaemia, hypophosphataemia, hypocalcaemia, hypoglycaemia, elevated urea levels. Hypophosphataemia and falling phosphate, hypokalaemia with a potassium of <2.5 mmol/L, and hypoglycaemia (glucose <3 mmol/L) all represent an imminent risk to life in AN
thyroid function tests
Test
Should be considered as part of initial screening panel and in follow-up visits if abnormalities are identified.
Low T3 levels are common but patients typically have normal TSH and thyroid supplementation should not be given.
Result
triiodothyronine (T3) low, thyroxine (T4) normal, thyroid-stimulating hormone (TSH) normal (changes are not generally clinically significant)
liver function tests
Test
Non-diagnostic, but an initial screening is recommended.
Should be monitored upon follow-up visits if weight loss continues.
Elevations of hepatic enzymes are generally mild in AN, but more severe elevations have been associated with acute presentations. Liver function should improve with re-feeding.
Other causes for transaminitis, such as alcoholism, paracetamol (acetaminophen) overdose, medications toxic to the liver, and gallstones should also be considered.
Serum cholesterol may be high in acute AN and is expected to normalise with re-feeding.
Result
elevated alanine aminotransferase, aspartate aminotransferase; elevated cholesterol
blood glucose
Test
May be recommended as part of the initial assessment.
Result
Low blood glucose may be related to nutritional restriction.
urinalysis
Test
May be useful to assess hydration status; also, ketonuria may be present acutely.
Result
low specific gravity may indicate consumption of large quantities of free water; ketonuria may indicate significant semi-starvation
Investigations to consider
Sick, Control, One, Fat, and Food (SCOFF) questionnaire
Test
A structured 5-item scale that is frequently used for screening in both adolescents and adults (although note that it is only validated in adults).[76] SCOFF has high sensitivity and specificity, particularly in young women, but its predictive value may be reduced for other patient groups, and for those with atypical presentations of AN.[76][77][78][79] UK guidance (from NICE) cautions against the use of screening tools (e.g., SCOFF) as the sole method to determine whether or not a person has an eating disorder; if utilised, screening tools should act as an adjunct to a more comprehensive clinical assessment.[67]
Includes the following questions:
"Do you ever make yourself sick because you feel uncomfortably full?"
"Do you worry that you have lost control over how much you eat?"
"Have you recently lost more than one stone in a 3-month period?"
"Do you believe yourself to be fat when others say you are too thin?"
"Would you say that food dominates your life?"
Result
Presence of 2 or more positive answers is suggestive of an eating disorder (AN or bulimia nervosa).
ECG
Test
Consider if there are electrolyte abnormalities, bradycardia, chest pain, hypotension, previous cardiac abnormalities, or use of medications or illicit drugs that could compromise cardiac functioning.[67] US guidance recommends that an electrocardiogram be done in all patients with a restrictive eating disorder.[68]
Result
bradycardia, conduction defects; prolongation of QT interval (corrected for rate). High risk features on ECG include prolonged QTc (<18 years males >450 ms, females >460 ms; ≥18 years: males >430 ms, females >450 ms), heart rate <40 bpm, and arrhythmia associated with malnutrition and/or electrolyte disturbances
bone densitometry (dual-energy x-ray absorptiometry)
Test
UK guidance recommends consideration of bone densitometry after 1 year of underweight in children and young people (earlier if they have recurrent bone pain or fractures) and after 2 years of underweight in adults (earlier if they have bone pain or recurrent fractures).[67] According to US guidance, clinicians should consider bone densitometry for those with amenorrhoea for more than 6-12 months.[68][72]
Helps to illustrate effects of severe weight loss to patients who deny or minimise the presence of eating disorder symptoms.
Result
osteopenia, osteoporosis
estradiol in females
Test
Non-diagnostic, but helpful to rule out other causes of amenorrhoea and to monitor physiological effects of disease.
Result
low or non-detectable levels
testosterone in males
Test
Non-diagnostic, but helpful to monitor physiological effects of disease.
Result
low levels
urine or serum pregnancy test
Test
Excludes pregnancy in the presence of amenorrhoea.
Result
Positive result confirms pregnancy
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