What Labs to Consider with REDs
Evaluating specific blood work is one critical component of diagnosing and treating Relative Energy Deficiency in Sport (REDs). Getting labs done provides valuable objective data; however, it's important to note this represents just one part of a comprehensive clinical picture when identifying and managing energy availability issues.
Here is a breakdown of key lab panels that help screen for REDs:
Hematological
CBC (Complete Blood Count): Flags low iron status, red blood cell changes, and immune system shifts. It can also identify compromised immune function, such as reduced white blood cell count (WBCs).
Iron Status
Iron, TIBC & Ferritin Panel: Chronic physiological stress combined with underfueling disrupts ferritin (stored iron) metabolism and impairs iron status. New clinical guidelines as of Sept 2026 for ferritin are as follows:
30 ng/mL: recommended ferritin cut off for diagnosing iron deficiency in adults
50 ng/mL: may be appropriate when symptoms are or ongoing risks factors are present
*note there isn’t a specific guideline for runners, but based on evidence around performance having a value > 40 ng/mL is a safe recommendation along with interpreting other iron related biomarkers
Electrolytes & General Health
CMP (Comprehensive Metabolic Panel): Helps uncover electrolyte, liver, and kidney imbalances caused or exacerbated by REDs.
Growth & Development
IGF-1: A primary marker for growth, bone health, and physical recovery. Lower values highlight the body's underfueled state.
Thyroid Function
TSH, Total & Free T3, Free T4: REDs can suppress thyroid function and slow overall metabolism to conserve energy. Note that thyroid markers landing in the lower quartile—even when technically inside the "clinically normal" range—often indicate underlying REDs.
Reproductive Hormones
LH, FSH, Estradiol (females), Total & Free Testosterone (males), and Progesterone: Underfueling suppresses reproductive signaling pathways. This disruption impacts menstrual cycles, fertility, sleep quality, bone health, and athletic performance.
Bone & Mineral Metabolism
25-OH Vitamin D: Low energy availability (LEA) impairs nutrient absorption, impacting bone and mineral health. Checking Vitamin D levels identifies deficiencies that weaken bones, delay recovery, and heighten injury risk. Evidence supports maintaining a Vitamin D level of 50 ng/mL for athletes.
Glucose & Lipid Metabolism
Fasting Glucose, Insulin, and Lipid Panel: In an energy-deficient state, the body adapts to conserve resources. This can result in lower or unstable blood sugar, altered insulin sensitivity, and abnormal cholesterol profiles.
Important Considerations for Testing
Schedule when healthy: Draw labs only when free from acute illness.
Rest prior: Avoid hard training for 48 hours leading up to the blood draw.
Pause supplements: Hold iron and other dietary supplements for 48 hours prior to testing.
Look beyond the labs: REDs diagnosis is never based on laboratory results alone.
Getting specific blood work done is just one important part of the process when diagnosing and treating REDs. Lab findings must be integrated with a full assessment of symptoms, training load, and dietary intake.
As sports dietitians, we interpret these specific markers and symptoms to build individualized nutrition plans that target REDs prevention or recovery, protect long-term health, and optimize athletic performance!
Want your own labs? Check out our own labs where you can order through Quest and follow up with us for how to manage these values in a 45 minute appointment once results are received.
Sources: PMID: 37752011, PMID: 37752010