An FSH to LH Ratio Calculator is a clinical tool use in endocrinology and reproductive medicine to help diagnose certain hormonal imbalances, most notably Polycystic Ovary Syndrome (PCOS) in women. The calculator takes the blood test results for two critical pituitary hormones—Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH)—and computes the ratio between them. In a normal menstrual cycle, these hormones are release in a balanced way. However, in certain conditions like PCOS, the level of LH is often disproportionately high compared to FSH, leading to an elevated ratio. Consequently, this calculated ratio serves as a significant diagnostic clue for healthcare professionals when evaluating causes of infertility, irregular periods, and other hormonal issues.
formula of Fsh Lh Ratio Calculator
The formula to calculate the FSH to LH ratio is a simple division of the two hormone levels.
FSH to LH Ratio Formula
This is the primary formula for the calculator. It is a direct division of the FSH value by the LH value.
Formula:
FSH/LH Ratio = FSH Level / LH Level
- FSH Level: The measured blood level of Follicle-Stimulating Hormone.
- LH Level: The measured blood level of Luteinizing Hormone.
Required Inputs and Units
To ensure a meaningful calculation, both hormone levels must be measured on the same day (ideally in the early follicular phase of the menstrual cycle) and reported in the same units. The standard unit is milli-international units per milliliter (mIU/mL).
- Input 1: FSH Level (in mIU/mL)
- Input 2: LH Level (in mIU/mL)
Interpreting the FSH/LH Ratio
The interpretation of the FSH/LH ratio is a key part of a hormonal assessment, especially in the context of PCOS evaluation.
| FSH/LH Ratio | General Interpretation |
| Approximately 1:1 | A ratio close to 1 is typically seen in the early follicular phase of a normal menstrual cycle. |
| Less than 1 | An "inverted" or "reversed" ratio, where LH is higher than FSH. |
| Greater than 2:1 or 3:1 | A significantly inverted ratio (where LH is 2x or 3x higher than FSH) is strongly suggestive of Polycystic Ovary Syndrome (PCOS). |
Example of Fsh Lh Ratio Calculator
A physician is evaluating a patient for irregular menstrual cycles and other symptoms. A blood test is ordered on day 3 of her cycle.
First, the lab results are obtained.
- FSH Level: 6.0 mIU/mL
- LH Level: 18.0 mIU/mL
Next, the physician (or a calculator) computes the ratio.
FSH/LH Ratio = FSH Level / LH Level
FSH/LH Ratio = 6.0 / 18.0 = 0.333...
It is often easier to interpret this by looking at the LH to FSH ratio:
LH/FSH Ratio = 18.0 / 6.0 = 3
This means the LH level is 3 times higher than the FSH level, resulting in an LH:FSH ratio of 3:1. This is a classic finding that is highly suggestive of PCOS and would prompt further investigation.
Most Common FAQs
Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH) are two crucial reproductive hormones produced by the pituitary gland in the brain. In women, FSH stimulates the growth of ovarian follicles (which contain the eggs) at the beginning of the menstrual cycle. LH is responsible for triggering ovulation (the release of an egg) and stimulating the production of other hormones.
The levels of FSH and LH fluctuate significantly throughout the menstrual cycle. The baseline relationship between them is best assessed during the early follicular phase (typically days 2, 3, or 4 of the cycle), which is the period right after menstruation begins. Measuring the ratio at other times, such as near ovulation when there is a natural LH surge, would not be diagnostically useful for evaluating PCOS.
No. While an inverted or high LH to FSH ratio (e.g., >2:1) is a strong indicator, it is not sufficient for a diagnosis on its own. The official diagnosis of PCOS is typically made using the Rotterdam criteria, which require a patient to have at least two of the following three conditions: 1) irregular or absent ovulation, 2) clinical or biochemical signs of high androgen levels, and 3) polycystic ovaries as seen on an ultrasound. The FSH/LH ratio is a key part of the biochemical evaluation.