31st January 2024

Blood tests

U&Es – hyponatraemia may indicate water loading, where a patient tries to disguise weight loss by drinking large amounts of water prior to their appointments. This can be checked by testing urine osmolality. Hypokalaemia could indicate purging or laxative abuse, and <2.5mmol/L is a red flag. Both can occur in malnutrition. Also, look for acute kidney injury. A normal creatinine might reassure, but note the low muscle mass and low protein intake, a creatinine within reference ranges may be raised for that individual.
VBG: metabolic acidosis can indicate laxative abuse, whereas alkalosis can indicate vomiting.
Liver function tests – transanimases are often raised. This is thought to be due to the process of gluconeogenesis, especially from body proteins. Transanimases 3x the baseline is a reg flag. A raised gamma GT could indicate vomiting, as could a raised amylase.
Bone profile: Hypomagnesemia is found in malnutrition. Phosphate is key to monitor for refeeding syndrome. A normal phosphate is not necessarily reassuring, as does not indicate body stores. It can suddenly drop without warning, especially in someone who has not eaten for more than 48 hours.
Thyroid function tests: hypothyroid picture caused by low iodine diet
Vitamin D: if low can exacerbate psychological symptoms and give a depressive picture
Blood glucose: hypoglycaemia usually indicates poor body reserves, a red flag is <3mmol/L
FBC: WCC can drop, especially neutrophils in starvation. Also to look for anaemia, a Hb <10g/L is a red flag.
B12, Folate and Ferritin: to investigate the nutritional deficiency that can cause anaemia
Creatinine Kinase: can sometimes be done to investigate excessive exercise
HbA1c – useful if a patient had diabetes and omitting insulin. >86mmol/mol is a red flag for admission.

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