LH (Luteinizing Hormone)
Luteinizing hormone (LH) is produced by the pituitary gland and triggers ovulation when it surges mid-cycle. The LH surge causes the dominant follicle to release its egg, making it critical for fertility timing.
LH levels are low in the follicular phase, spike dramatically at mid-cycle (the LH surge), and return to baseline in the luteal phase. An elevated LH/FSH ratio > 2:1 may suggest PCOS.
Note: Reference ranges vary by cycle phase. Source: Endocrine Society.
What It Measures
Pituitary hormone that triggers ovulation and supports the corpus luteum.
Reference Ranges
| Status | Range (mIU/mL) |
|---|---|
| Optimal | 1.9–12.5 mIU/mL (follicular) |
| Normal | 8.7–76.3 mIU/mL (mid-cycle surge) |
| Borderline | 0.5–16.9 mIU/mL (luteal) |
| Out of Range | Range varies by cycle phase — consult provider |
Range by Cycle Phase
| Cycle Phase | Reference Range |
|---|---|
| Follicular | 1.9–12.5 mIU/mL (days 1–13) |
| Ovulatory | 8.7–76.3 mIU/mL (LH surge, 24–36h before ovulation) |
| Luteal | 0.5–16.9 mIU/mL (days 17–28) |
| Menopause | 15.9–54.0 mIU/mL |
Source: Endocrine Society, ACOG. Ranges are approximate — consult your provider.
When to test: Day 3 for baseline. Serial testing to detect LH surge for fertility timing.
Interpreting Your Results
When Values Are High
Elevated LH/FSH ratio > 2:1 may indicate PCOS. High LH without surge pattern suggests anovulation.
When Values Are Low
Hypothalamic or pituitary dysfunction. Suppressed by stress, low body weight, or hypothalamic amenorrhea.
How GATOR Tracks This
Lab Providers
Related Clinical Ratios
Related Biomarkers
This content is for informational purposes only and does not constitute medical advice. Reference ranges may vary by laboratory and individual factors. Consult a qualified healthcare provider for interpretation of your results and treatment decisions.
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