Hertility’s research conducted the ‘largest study ever undertaken’ in this area, across five years.

Hertility, an Irish founded UK and Irish healthcare provider for women, has today (19 August) published the ‘largest study ever undertaken’ in the region, on female testosterone levels.

Published in the Journal of Endocrinological Investigation, Hertility assessed data from 30,453 women aged between 18 and 74 who accessed at-home hormone testing in England, Scotland and Wales between September 2020 and August 2025.

What was discovered is that hormone levels decline progressively throughout adult life, falling by approximately 1.4pc each year from a woman’s 20s onwards, with no abrupt perimenopausal cliff edge, which is the term often used to describe the sudden, ‘cliff-like’ drop in hormones. 

Testosterone plays a crucial role in many of the body’s functions, such as libido, mood, bone mineral density, muscle mass and metabolic function and also forms part of the assessment of conditions including PMO and androgen deficiency. However, the data has thus far not kept pace with developments. 

Currently, in both Ireland and the UK testosterone is typically measured using the immunoassay method. The ‘normal’ ranges that inform the tests are frequently based on just two small validation studies which took data from only 149 women across two broad age ranges 20 to 49 and the over 50s.  

Additionally, that cohort was screened only for BMI and hormonal contraceptive use and it failed to exclude hirsutism, which is excessive hair growth, PMOS, which is formerly PCOS and other markers of androgen excess. 

As a result, the research found that the dependence on arguably outdated data means “some women are still being falsely reassured and others investigated unnecessarily after their testosterone levels are tested.”

Failing averages

The report suggested that tests based on averages are failing women, particularly when it is shown that testosterone variation widens with age. 

Consider for a moment a woman of 25, within a bracket of 19 to 59 years olds, whose results may be regarded as normal, but who may have a counterpart whose results are flagged as abnormal and investigated because she is being compared against a system that was not designed to reflect her age. 

The report noted, “genuine hormonal disruption is masked as being ‘normal’ while normal physiology is escalated as abnormal and both outcomes contribute to the diagnostic delays that continue to characterise women’s health.

“Instead of using a single cut-off point, the researchers modelled where testosterone levels typically fall at every single year of age. This means a woman’s result can be shown as its precise position within the normal range for her age, providing one piece of evidence to be weighed alongside her symptoms, cycle history, medication use and a clinical examination.”

Hertility’s report is calling on clinical laboratories, assay manufacturers and guideline bodies to use age-specific, age-continuous hormone ranges rather than a ‘one-size-fits-all’ approach to women’s health. They should also aim to share the criteria that formed the basis of their study so clinicians can make an informed decision. 

Commenting on the report, Dr Helen O’Neill, the CEO of Hertility and associate professor in reproductive and molecular genetics at UCL, said, “When a woman has a hormone test, she is looking for an answer about her own body. 

“What she receives is a comparison against an average and too often an average drawn from a few dozen women, decades ago, grouped into age brackets so broad they are almost meaningless.

“Averages are not neutral, they flatten the range of normal human variation, masking real hormonal disruption in some women while manufacturing false alarm in others.

“Precision medicine requires reference data of sufficient scale and rigour that an individual can be interpreted as an individual. Better reference ranges will never replace clinical judgement, but they change what clinical judgement has to work with, and set a standard for what should be expected before any hormone result is described as normal or abnormal for a woman.”

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