🏃‍♀️ Female Athlete / Missing Periods (RED-S)

What this panel can settle, and by what logic

The single question this panel answers is whether the axis is switched off centrally or has failed peripherally, and it answers it with three markers read together rather than with any one of them.

Low LH & FSH with a low Estradiol, Sensitive (LC/MS-MS) is hypothalamic suppression. The pituitary has stopped signaling because energy availability is too low, so both gonadotropins are down and the ovary is quiet behind them. That is the opposite of primary ovarian insufficiency, where the ovary fails and FSH climbs above 25 IU/L trying to drive it. The LH-to-FSH relationship is measurably different in functional hypothalamic amenorrhea from other causes of a missing period Boegl 2024, and it is the discrimination this panel exists for.

A low Free T3 (Triiodothyronine) under a normal TSH (Thyroid-Stimulating Hormone) corroborates it. Low energy availability downregulates peripheral conversion of T4 to T3 without the pituitary registering hypothyroidism, so free T3 sits at 2.1 pg/mL under a TSH of 1.4 mIU/L. Read alone that pattern gets mislabeled as thyroid disease; read next to a suppressed LH it is part of one coherent story Mountjoy 2023.

IGF-1 (Insulin-like Growth Factor 1) adds the anabolic half. IGF-1 falls with sustained energy deficit, and its fall is one of the more consistent findings in the RED-S biomarker literature Dvořáková 2024. Alongside Ferritin and Vitamin D (25-Hydroxy), which decide whether bone has the raw material to rebuild at all, that gives a picture no single marker does.

What it cannot settle, and what would

It cannot measure your bones, and your bones are the outcome that matters. The bone loss driven by years of low estradiol is the part of this syndrome that can be permanent, and it is measured by DEXA, not by blood Mountjoy 2023. A woman with 3 years of amenorrhea and a perfect panel still needs the scan. If you buy one thing after this page, buy that.

It cannot confirm RED-S as a diagnosis, because there is no confirmatory blood test and the field knows it. A 2024 review of biomarkers used for RED-S identified 79 candidate markers across six categories, and only 7 of 13 studies reached even a 60% agreement rate on which ones to use Dvořáková 2024. The 2023 IOC consensus makes energy availability and its clinical consequences the diagnosis, with laboratory markers as support Mountjoy 2023.

It cannot exclude pregnancy, a prolactinoma or PCOS, which are the three other reasons periods stop. Pregnancy is a $10 test, Prolactin is on no version of this panel, and PCOS runs in the opposite hormonal direction.

And it cannot tell you how much to eat. That is a sports dietitian's job, and the panel's real function is to make the case that one is needed — which, in a sport where under-fueling is often praised, is most of the battle Mountjoy 2023.

Draw conditions that decide whether the money is wasted

An athlete's panel has one condition nobody else's has: the training you did yesterday is a confounder.

1. Not the morning after a hard session, and ideally 48 hours clear. Acute exercise moves Cortisol (AM), IGF-1 (Insulin-like Growth Factor 1) and the Comprehensive Metabolic Panel (CMP)'s muscle enzymes at once, which turns a panel about chronic energy deficiency into a snapshot of Tuesday's intervals Dvořáková 2024.
2. Cortisol (AM) before 9am, fasted. The rhythm makes an afternoon value uninterpretable, and cortisol is the marker in this panel most often drawn at the wrong time.
3. Note the cycle day, or note that there is not one. Estradiol, Sensitive (LC/MS-MS) and LH & FSH are read against phase-specific intervals; if periods are absent, that itself is the information Boegl 2024. Draw days 2 to 5 if you are still cycling.
4. No biotin for 72 hours Li 2020, and no iron in the 5 days before, which lifts the Iron Panel (Iron, TIBC, Transferrin Saturation) without lifting the Ferritin the panel is actually asking about Cancado 2025.

How you would know it answered your question, and what each pattern means next

Four patterns, and the timescale each one runs on. None of them is measured in days.

• Low LH & FSH with low Estradiol, Sensitive (LC/MS-MS): hypothalamic suppression from energy deficiency. The next steps are a sports physician, a dietitian and a DEXA scan Mountjoy 2023. Retest hormones at 6 months, not at 6 weeks — the axis restarts on the timescale of restored energy availability and body mass, not of a supplement Boegl 2024.
• High LH & FSH with low estradiol: this is not RED-S. FSH above 25 IU/L points at the ovary and needs Anti-Müllerian Hormone (AMH) and a gynecologist Boegl 2024.
• Low Free T3 (Triiodothyronine) with a normal TSH (Thyroid-Stimulating Hormone): supportive of energy deficiency, and specifically NOT a reason to start thyroid hormone Mountjoy 2023. Recheck at 3 months of adequate fueling and watch IGF-1 (Insulin-like Growth Factor 1) move with it Dvořáková 2024.
• Ferritin under 30 ng/mL or Vitamin D (25-Hydroxy) under 30 ng/mL: treat both, because bone rebuilding needs the substrate and stress fractures are the presenting complaint here as often as fatigue is. Retest ferritin at 12 weeks Cancado 2025 and vitamin D at 12 weeks, allowing for the ±5% assay bias that the standardization program still measures between platforms Wise 2021.

Sources read for these sections

• Mountjoy M, et al. 2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). British Journal of Sports Medicine 2023 · PMID 37752011
• Dvořáková K, et al. A literature review of biomarkers used for diagnosis of relative energy deficiency in sport. Frontiers in Sports and Active Living 2024 · PMID 39070233
• Boegl M, et al. The LH:FSH Ratio in Functional Hypothalamic Amenorrhea: An Observational Study. Journal of Clinical Medicine 2024 · PMID 38592037
• Wise SA, et al. Vitamin D Standardization Program (VDSP) intralaboratory study for the assessment of 25-hydroxyvitamin D assay variability and bias. Journal of Steroid Biochemistry and Molecular Biology 2021 · PMID 34010687
• Cancado RD. Defining Global Thresholds for Serum Ferritin: A Challenging Mission in Establishing the Iron Deficiency Diagnosis in This Era of Striving for Health Equity. Diagnostics (Basel) 2025 · PMID 39941219
• Li D, Ferguson A, Cervinski MA, Lynch KL, Kyle PB. AACC Guidance Document on Biotin Interference in Laboratory Tests. J Appl Lab Med 2020 · PMID 32445355