The frequency of blood tests will depend on the condition and severity. If the condition is stable, we would advise blood tests on a 3-6 month basis.
Possible explanations for abnormal blood results
Sodium – Hyponatremia is common in patients with anorexia nervosa. This could be due to non-specific changes of chronic disease, but may also indicate water loading. Water loading often exists to ward off hunger, or in some cases, to falsify weight. We would normally not act unless sodium falls below 125.
Potassium – Hypokalemia is extremely common in anorexia nervosa purging subtype and severe bulimia nervosa. Please see our guidance on purging
Urea - Low urea is commonin low weight patients due to general malnutrition. A high urea (even with a normal creatinine) is concerning as it may indicate dehydration or renal failure
Creatinine – Creatinine is generally low in low weight patient due to reduced lean mass. A high Creatinine is concerning as this may indicate renal failure which could be due to dehydration or chronic purging.
Liver Function Tests – These can become abnormal in either starvation or refeeding phases. Normally they remain under 200, but can be greatly elevated in hepatic ischaemia due to volume depletion / hypotension. We normally apply a ‘watchful wait’ with frequent monitoring. If there are concerns about liver failure, an INR and clotting screen may help.
Phosphate – This is important to monitor especially if patient is opting to re-feed in the community. On the ward, we would test this daily for ten days, but this may not be possible in a primary care setting. A falling phosphate would likely be due to ‘refeeding syndrome’ which can be fatal. This is why it is important to re-feed in a slow and steady fashion. If phosphate falls below 0.8, we would normally supplement with Phosphate-Sandoz (two to six per day depending on level of depletion). If phosphate falls below 0.5 we would recommend admission to the acute hospital for phosphate infusion.
A raised phosphate could mean that the patient is abusing laxatives.
Magnesium - This is important to monitor especially if patient is opting to re-feed in the community. On the ward, we would test this daily for ten days, but this may not be possible in a primary care setting. A falling magnesium would likely be due to ‘refeeding syndrome’ which can be fatal. This is why it is important to re-feed in a slow and steady fashion. If magnesium falls below 0.8, we would normally prescribe magnesium supplements.
Hypomagnesemia may also occur in diuretic abuse.
Creatine Kinase – This is worth monitoring if you suspect excessive exercise. A raised CK may be indicating muscle breakdown. Normally levels remain under 500, so levels above this may indicate more serious causes.
Full Blood Count - Anaemia is common in low weight patients and is likely to be nutritional. The WCC can help to monitor weight changes especially in patients who refuse to be weighed or are suspected of falsifying their weight. A falling WCC often occurs in relation to falling weight. A WCC of less than 2.0 is extremely concerning. A decreased neutrophil count is normally the culprit but we normally only act when this falls below 0.5, in which case prophylactic antibiotics are used.
Cholesterol - Cholesterol is often raised in Anorexia Nervosa. This needs careful explanation to the patient as it often confuses, leading to further cutting back of fatty foods, which perpetuates the problem. You can reassure them that if they restore their weight, the cholesterol will normalise.
There are many hypotheses for this paradox including increased levels of cholesterylester transfer protein which increases cholesterol turnover as an adaptation to its low intake. Also, starvation results in increased synthesis of lipoprotein and these lipoproteins are transporting fats in the body which the body is relying on as fuel due to insufficient food intake.
If you have a friend or family member with an eating disorder and you want to learn ways to help them, come along to our Carer's Workshop in Bolton, starting on Monday 22nd January. Contact your Eating Disorder Team for more info. [x] Close
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