Endo Fha Diagnostic Evaluation Cycle Length

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name: endo-fha-diagnostic-evaluation-cycle-length
description: This skill directs clinicians to initiate a diagnostic workup for functional hypothalamic amenorrhea (FHA) when menstrual cycles persistently exceed 45 days or amenorrhea lasts three months or longer. Trigger phrases include 'cycle longer than 45 days' or 'three months of no menses warrants evaluation'.
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# Diagnostic evaluation for FHA based on cycle length or amenorrhea duration

## STEP 1 — Gather Information
Collect menstrual history (cycle length, duration of amenorrhea), perform urine pregnancy test, and assess for weight change, exercise intensity, stressors, and eating disorder symptoms. If pregnancy is negative and history suggests possible FHA, proceed to step 2.

## STEP 2 — Rule In / Rule Out
Determine whether menstrual cycle interval persistently exceeds 45 days OR amenorrhea duration is 3 months or longer. If yes, rule in FHA as suspected; if no, consider alternative diagnoses and stop FHA-specific workup.

## STEP 3 — Classify or Stratify
For patients ruled in, classify as suspected FHA and initiate baseline endocrine evaluation (TSH, free T4, prolactin, LH, FSH, estradiol, AMH) and consider a progestin challenge to assess estrogen exposure. If labs suggest alternative pathology, pursue those diagnoses.

## STEP 4 — Decide
If baseline labs are consistent with FHA (low/normal LH, FSH, low estradiol, normal TSH/prolactin) and no organic cause identified, diagnose FHA and start multidisciplinary management; otherwise, treat identified etiology.

## Clinical Guardrails / Mimics / Pitfalls
Mimics: pregnancy, thyroid dysfunction, hyperprolactinemia, PCOS, outflow tract obstruction, chronic illness. Pitfalls: diagnosing FHA without excluding pregnancy, overlooking subtle thyroid dysfunction, misattributing normal adolescent cycle variability to FHA, initiating hormone therapy without confirming estrogen deficiency.

## Concrete Clinical Example
A 17-year-old runner reports menstrual cycles every 5–6 weeks for the past 5 months, denies pregnancy, weight stable, exercises 2 hours daily. Pregnancy test negative. Cycle length >45 days triggers FHA evaluation; baseline labs show LH 3 mIU/mL, FSH 4 mIU/mL, estradiol 18 pg/mL, TSH normal. No organic cause found; FHA diagnosed and energy balance correction initiated.

**Source:** Functional Hypothalamic Amenorrhea: An Endocrine Society Clinical Practice Guideline, Endocrine Society, 2017, https://doi.org/10.1210/jc.2017-00131