What does it measure?
The calculation divides the measured LH concentration by FSH from the same assessment. Both hormones come from the pituitary gland and change with reproductive stage. Combining them does not remove the natural variation present in each result.
Before reading the calculation
- Inputs
- Calculated from LH and FSH measured at the same cycle stage, using compatible units.
- Context
- Record cycle day; the natural LH surge can change the ratio.
What can the result mean?
A higher ratio may occur in some people with polycystic ovary syndrome, but also during a normal LH surge. Many people with PCOS do not have an elevated ratio. A lower ratio likewise has no single diagnosis attached to it. [1]
Calculated from LH and FSH measured at the same cycle stage, using compatible units.
- Context
- Record cycle day; the natural LH surge can change the ratio.
When is it useful, and how is it read?
When irregular periods or androgen-related symptoms are the concern, the clinical history and appropriate diagnostic criteria lead the assessment. The separate LH and FSH results may add context, but dividing them does not replace an evaluation for PCOS or other possible causes. [1] [2]
What can affect it?
Cycle timing, pulsed hormone release, hormonal contraception, fertility treatment, and menopause can all alter the result. Research that measured these hormones repeatedly through the cycle found substantial overlap between people with and without PCOS, limiting the ratio's diagnostic usefulness. [1]
A high ratio does not diagnose PCOS
The LH-to-FSH ratio varies across the cycle and overlaps between people with and without polycystic ovary syndrome. It cannot confirm PCOS, and a ratio within range cannot rule it out. [1]
Questions you might have
Can this ratio diagnose PCOS?
No. Research found considerable overlap between people with and without PCOS. The ratio cannot confirm or exclude the condition. [1]
Can the ratio change without a new disorder?
Yes. LH and FSH vary through the cycle, so sampling time can change the calculation. [1]
What comes next?
If the concern is irregular periods, acne, or excess hair growth, a clinical assessment and appropriately selected androgen tests are more useful starting points. Your clinician can explain which diagnostic criteria apply and whether further testing is needed. There is no reason to treat the ratio itself. [1]
What evidence beyond this ratio supports or argues against the diagnosis being considered?
The reference interval and units on your report are part of understanding your result. Understand units, reference intervals, and treatment targets.
Sources & references
Medical references & original research
Books we consulted
References that informed our explanations of the test and its context.
- Pagana KD, Pagana TJ, Pagana TN. Mosby’s Diagnostic and Laboratory Test Reference. 14th ed. Elsevier; 2019.
Practical-section sources accessed: .
For general health education. Interpreting your result and deciding on tests or treatment requires your health context and a qualified clinician.
