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Adolescent Anorexia Nervosa: Admission and Refeeding Case [ Case Discussion ](https://mdster.com/blog?category=case-discussion) Adolescent Anorexia Nervosa: Admission and Refeeding Case =========================================================== Clinical reasoning for medical instability, refeeding hypophosphatemia, involuntary nutrition, and return to sport [ MDster Editorial Team ](https://mdster.com/about) · Aug 13, 2026 · 5 min read · 32 [ Reviewed by Dr. Ali Ragab, MBBCH, MSc, MCAI ](https://mdster.com/medical-reviewers/dr-ali-ragab) [Editorial Policy](https://mdster.com/editorial-policy) | [Corrections Policy](https://mdster.com/corrections) [ Board Review ](https://mdster.com/blog?tag=board-review) [ Pediatrics ](https://mdster.com/blog?tag=pediatrics) [ Adolescent Medicine ](https://mdster.com/blog?tag=adolescent-medicine) [ Sports Medicine ](https://mdster.com/blog?tag=sports-medicine) [ Pediatric Eating Disorders ](https://mdster.com/blog?tag=pediatric-eating-disorders) [ Refeeding Syndrome ](https://mdster.com/blog?tag=refeeding-syndrome) ![Adolescent Anorexia Nervosa: Admission and Refeeding Case](https://mdster.com/storage/blog/images/adolescent-anorexia-nervosa-admission-and-refeeding-case.jpg) Share this article Share this post On this page 1. [ Case Formulation and Differential Diagnosis ](#case-formulation-and-differential-diagnosis) 2. [ Why This Patient Requires Admission ](#why-this-patient-requires-admission) 3. [ Initial Investigation and Stabilization ](#initial-investigation-and-stabilization) 4. [ Refeeding Syndrome and Hypophosphatemia ](#refeeding-syndrome-and-hypophosphatemia) 5. [ Managing a Phosphate of 2.2 mg/dL ](#managing-a-phosphate-of-22-mgdl) 6. [ Clinical Application: Recovery Beyond Stabilization ](#clinical-application-recovery-beyond-stabilization) 7. [ Key Points for Board Exams ](#key-points-for-board-exams) 8. [ Conclusion ](#conclusion) 9. [ Frequently Asked Questions ](#blog-faqs) 10. [ References ](#references-heading) On this page 1. [ Case Formulation and Differential Diagnosis ](#case-formulation-and-differential-diagnosis) 2. [ Why This Patient Requires Admission ](#why-this-patient-requires-admission) 3. [ Initial Investigation and Stabilization ](#initial-investigation-and-stabilization) 4. [ Refeeding Syndrome and Hypophosphatemia ](#refeeding-syndrome-and-hypophosphatemia) 5. [ Managing a Phosphate of 2.2 mg/dL ](#managing-a-phosphate-of-22-mgdl) 6. [ Clinical Application: Recovery Beyond Stabilization ](#clinical-application-recovery-beyond-stabilization) 7. [ Key Points for Board Exams ](#key-points-for-board-exams) 8. [ Conclusion ](#conclusion) 9. [ Frequently Asked Questions ](#blog-faqs) 10. [ References ](#references-heading) A resting HR of 42 bpm in a cachectic adolescent athlete is not benign athletic conditioning. Combined with hypotension, rapid weight loss, amenorrhea, hypothermic physiology, and severe restriction, it signals cardiovascular adaptation approaching decompensation. Case Formulation and Differential Diagnosis ------------------------------------------- This 16-year-old has **anorexia nervosa, restricting type**, supported by energy restriction, low weight, distorted weight perception, and compulsive exercise. Amenorrhea is not required for diagnosis but reflects hypothalamic suppression from low energy availability. Relative Energy Deficiency in Sport (REDs) describes the resulting multisystem physiology, not an alternative psychiatric diagnosis. [\[1\]](#cite-1 "Reference [1]") Important alternatives and contributors include: - Hyperthyroidism, diabetes mellitus, celiac disease, and inflammatory bowel disease - Pregnancy and other causes of secondary amenorrhea - Malignancy, chronic infection, or systemic inflammatory disease - ARFID, major depression, OCD, substance use, or covert purging Her lanugo, acrocyanosis, low-voltage ECG, bradycardia, and cold extremities reflect reduced metabolic rate, peripheral vasoconstriction, and loss of cardiac and skeletal muscle mass. Why This Patient Requires Admission ----------------------------------- Current SAHM criteria support hospitalization when **one or more** indicators of medical or psychiatric instability are present. Clinical trajectory and available family support remain important; admission should never depend on BMI alone. [\[2\]](#cite-2 "Reference [2]") FindingCurrent interpretationHR 42 bpmMeets severe daytime bradycardia criterion of less than 50 bpmBP 88/50 mmHgSystolic pressure is below the listed 90/45 mmHg thresholdTemperature 35.8°CConcerning, although above the SAHM cutoff of 35.6°COrthostatic HR rise of 32 bpmAbnormal and symptomatic, but below the updated threshold of more than 40 bpm for patients under 19 Thus, the severe bradycardia and hypotension independently justify admission. Rapid 9 kg weight loss, minimal caloric intake, dizziness, and excessive exercise further increase risk. > **Clinical Pearl:** Older examination resources may use an orthostatic HR rise above 20–25 bpm. Updated SAHM guidance uses a sustained rise above 40 bpm in adolescents younger than 19 years. Initial Investigation and Stabilization --------------------------------------- Evaluation should include: - CBC, electrolytes, bicarbonate, urea/creatinine, glucose, calcium, magnesium, and phosphate - AST/ALT, urinalysis, TSH, and pregnancy testing - ECG with manual review of rhythm and QTc - Focused testing for celiac disease, inflammation, or other diagnoses when clinically indicated - Assessment of suicidality, anxiety, depression, OCD symptoms, exercise compulsion, and purging Place the patient on supervised activity restriction and initiate cardiac monitoring when bradycardia, electrolyte disturbance, or ECG abnormalities warrant it. A QTc of 430 ms is not prolonged, but QTc must be followed because electrolyte abnormalities and QT-prolonging medications can increase arrhythmia risk. Refeeding Syndrome and Hypophosphatemia --------------------------------------- Refeeding shifts metabolism from catabolism to insulin-driven anabolism. Insulin moves phosphate, potassium, and magnesium intracellularly while increasing sodium and water retention; thiamine requirements also rise. The consequences can include arrhythmia, heart failure, respiratory weakness, seizures, and delirium. [\[3\]](#cite-3 "Reference [3]") Higher-energy, protocolized refeeding can be appropriate for many hospitalized adolescents and is preferable to prolonged underfeeding. Risk is driven substantially by the degree of malnutrition and magnitude or speed of preceding weight loss. Electrolytes should be monitored closely during the first week, when phosphate commonly reaches its nadir. [\[2\]](#cite-2 "Reference [2]") ### Managing a Phosphate of 2.2 mg/dL This represents moderate hypophosphatemia under the SAHM replacement protocol: 1. Give oral sodium-potassium phosphate providing 500 mg elemental phosphorus three times daily. 2. Recheck phosphate, potassium, magnesium, calcium, and renal function daily. 3. Continue nutritional rehabilitation while correcting the deficit. 4. For phosphate below 2.0 mg/dL or clinically significant symptoms, consider IV phosphate at 0.24 mmol/kg, maximum 15 mmol per dose, with PICU consultation. Institutional protocols and the patient’s renal function and serum potassium must guide prescribing. Evidence for universal prophylactic phosphate remains insufficient. [\[4\]](#cite-4 "Reference [4]") Clinical Application: Recovery Beyond Stabilization --------------------------------------------------- Family-based treatment is the first-line outpatient psychological treatment for adolescent anorexia nervosa, but it is inaccurate to call it the only evidence-supported therapy. Adolescent-focused therapy and eating-disorder-focused CBT may be appropriate when family-based treatment is unavailable, unacceptable, or ineffective. Medication should not replace nutritional rehabilitation or psychotherapy. [\[2\]](#cite-2 "Reference [2]") If she refuses essential NG nutrition, assess decision-making capacity rather than assuming incapacity from diagnosis alone. When starvation-related cognitive rigidity prevents appreciation of imminent risk, temporary treatment over objection may be ethically justified using parental permission, the least restrictive effective approach, and early ethics, psychiatry, and legal consultation. US requirements vary by state. [\[5\]](#cite-5 "Reference [5]") Competitive running remains contraindicated until she demonstrates: - Stable resting and orthostatic vital signs with normal electrolytes - Sustained nutritional intake supporting growth, weight restoration, and exercise expenditure - Progress toward an individualized treatment goal weight - Control of compulsive exercise and adherence to multidisciplinary treatment Menses resumption supports physiologic recovery but should not be the sole clearance criterion. Return-to-sport decisions should follow graded IOC REDs CAT2 risk assessment. [\[6\]](#cite-6 "Reference [6]") Key Points for Board Exams -------------------------- - Severe bradycardia or hypotension independently supports hospitalization. - Refeeding syndrome results from insulin-mediated electrolyte shifts; hypophosphatemia is its hallmark biochemical feature. - Do not stop effective refeeding for moderate, asymptomatic hypophosphatemia; replace and monitor. - Family-based treatment is first-line for adolescents. - OCD-spectrum symptoms are common, but depression, anxiety, and suicide risk require active assessment. Conclusion ---------- Medical stabilization is only the opening phase. Durable recovery requires weight restoration, family-supported psychotherapy, psychiatric care, and conservative, multidisciplinary return-to-sport decisions. Frequently Asked Questions ---------------------------- ### Does an orthostatic heart-rate rise of 32 bpm meet current admission criteria? Not by the updated SAHM threshold of more than 40 bpm for adolescents under 19. However, symptoms and other instability may still require admission. ### Should feeding stop when phosphate falls to 2.2 mg/dL? Usually not. Continue supervised nutrition, provide oral phosphate replacement, and monitor electrolytes closely unless severe symptoms or further deterioration occur. ### Is QTc prolongation intrinsic to anorexia nervosa? Not consistently. It often reflects electrolyte abnormalities or QT-prolonging medications, but it remains an important marker of arrhythmia risk. ### Must menstruation resume before return to competitive running? Not necessarily, but persistent amenorrhea indicates incomplete physiologic recovery. Clearance requires stable physiology, adequate energy availability, weight restoration, and psychological readiness. References (9) ------------------ 1. 1. [ AAP: Identification and Management of Eating Disorders in Children and Adolescents, 2021 ](https://publications.aap.org/pediatrics/article/147/1/e2020040279/33504/Identification-and-Management-of-Eating-Disorders) [↩](#cite-ref-1-1 "Back to text") 2. 2. [ Society for Adolescent Health and Medicine: Medical Management of Restrictive Eating Disorders in Adolescents and Young Adults, 2022 ](https://adolescenthealth.org/wp-content/uploads/2023/05/Medical-Management-of-Restrictive-ED-in-AYA.pdf) [↩](#cite-ref-2-1 "Back to text") 3. 3. [ doi.org/10.1002/ncp.10474 ](https://doi.org/10.1002/ncp.10474) [↩](#cite-ref-3-1 "Back to text") 4. 4. [ SAHM: Refeeding Hypophosphatemia in Hospitalized Adolescents With Anorexia Nervosa, 2022 ](https://adolescenthealth.org/wp-content/uploads/2023/05/Refeeding-Hypophosphatemia.pdf) [↩](#cite-ref-4-1 "Back to text") 5. 5. [ publications.aap.org/pediatrics/article/138/2/e20161485/52519/Informed-Consent-in-Decision-Making-in-Pediatric ](https://publications.aap.org/pediatrics/article/138/2/e20161485/52519/Informed-Consent-in-Decision-Making-in-Pediatric) [↩](#cite-ref-5-1 "Back to text") 6. 6. [ doi.org/10.1136/bjsports-2023-106994 ](https://doi.org/10.1136/bjsports-2023-106994) [↩](#cite-ref-6-1 "Back to text") 7. 7. [ APA Practice Guideline for the Treatment of Patients With Eating Disorders, 2023 ](https://www.psychiatry.org/psychiatrists/practice/clinical-practice-guidelines/eating-disorders) 8. 8. [ IOC Consensus Statement on Relative Energy Deficiency in Sport, 2023 ](https://bjsm.bmj.com/content/57/17/1073) 9. 9. 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