The Anti-Müllerian Hormone (AMH) test is widely used in reproductive health to offer insights into a person’s ovarian reserve. AMH is a hormone produced by the granulosa cells within the small, developing follicles of the ovaries. Measuring its level in the blood provides an estimate of the remaining supply of eggs, or the follicular pool. While generally considered a reliable indicator of ovarian reserve, the AMH test is not without its limitations and is subject to influences that can lead to questions about the accuracy of the result.
What the AMH Test Measures
The AMH test is a simple blood test that quantifies the concentration of Anti-Müllerian Hormone in the serum. AMH is secreted by the granulosa cells of the pre-antral and small antral follicles. Because AMH levels correlate strongly with the number of these growing follicles, the measurement serves as an indirect marker for the size of the remaining egg supply.
The hormone’s concentration remains relatively stable throughout the menstrual cycle, which is an advantage over other hormone tests that must be timed precisely. The result provides a quantitative “snapshot” of the ovarian reserve. AMH indicates the quantity of follicles, not the quality of the eggs they contain. This measurement is primarily used to predict how the ovaries might respond to stimulation during fertility treatments like In Vitro Fertilization (IVF). Higher levels typically suggest a better response to stimulation, while lower levels indicate a diminished reserve and a poorer response.
Biological Variables Affecting AMH Levels
AMH levels can be affected by various physiological factors, which may cause a result to be temporarily misleading if context is ignored. Hormonal birth control, such as the combined oral contraceptive pill, can temporarily suppress AMH levels. Studies show that AMH concentrations can be reduced by 15% to over 20% in women using these contraceptives. This suppression is not a true decline in ovarian reserve but a temporary dampening of the hormone’s production.
Vitamin D status also influences AMH concentration, as the hormone’s production seems regulated by the active form of Vitamin D. Low Vitamin D levels are associated with lower AMH readings. Supplementation in deficient women has occasionally been shown to increase AMH levels, suggesting a functional link.
Conditions that affect ovarian function also significantly impact AMH readings. Polycystic Ovary Syndrome (PCOS), for example, is frequently associated with AMH levels two to three times higher than average. This high reading is due to the large number of small, arrested follicles characteristic of PCOS, which actively secrete AMH, resulting in an artificially inflated concentration.
Procedural Sources of Test Inaccuracy
The test result can be inaccurate due to technical and handling errors that occur outside of the body. Pre-analytical errors, which happen before the sample is analyzed, pose a significant risk to result integrity. Improper sample collection, storage, or transport can lead to the degradation of the AMH protein, resulting in a falsely low reading. For instance, exposure to room temperature for more than 24 hours makes AMH measurements unreliable.
Analytical variability between different assay kits and generations of testing equipment introduces another layer of inaccuracy. Because there is no universal international standard for AMH measurement, different commercial assays are calibrated independently. This lack of standardization means a result from one laboratory may differ significantly from a result from another laboratory using a different system. Comparison studies have reported biases between different assays ranging from approximately -25% to +45% at clinically relevant concentrations.
Systematic error within the laboratory can also contribute to a misleading result. Issues like human error during processing, incorrect calibration of automated instruments, or problems with the reagents themselves can affect the final reported number. For example, certain older assay generations were known to have interference issues with serum components, which was addressed through new protocols, but highlights the potential for technical flaws. These variations can impact clinical decision-making, such as determining the correct dosage for ovarian stimulation.
Interpreting and Confirming AMH Results
When an AMH result seems unexpectedly high or low, it must be interpreted within the full clinical context, never in isolation. The AMH value should be evaluated alongside other markers of ovarian reserve. Complementary testing is routinely used to confirm the ovarian reserve status indicated by AMH.
The Antral Follicle Count (AFC), determined by a transvaginal ultrasound, is a direct visual assessment of the small follicles in the ovaries. This count is considered one of the most reliable predictors of ovarian response and can help validate or contradict the AMH level. Testing Follicle-Stimulating Hormone (FSH) and Estradiol levels, usually on the second or third day of the menstrual cycle, offers additional hormonal context.
If a result is suspicious of a technical error or was obtained while on a known suppressive factor like hormonal contraception, a retest may be recommended. The retest should be performed after stopping hormonal medication for one to three months to allow natural hormone production to resume. Consulting with a fertility specialist is the best course of action, as they synthesize all available data—AMH, AFC, FSH, and age—to provide the most accurate assessment of ovarian reserve and guide reproductive planning.