Summary

Bone density studies of puberty blockers (drugs that pause puberty) usually report averages. Sociologist Michael Biggs argued that averages hide the patients who matter most: those whose bone density falls into the abnormal range. He used individual data released with England's 2011–15 early puberty blocker study, covering 24 patients scanned after 2 years. On average, bone density fell well behind other teens of the same age and sex. About a third of patients had hip bone density low enough to count as low bone mass, found in only about 2 in 100 teens. More than a quarter had low spine density, and four were in the lowest 1 in 750. The study originally excluded children who already had low bone density, but this was relaxed in 2012. This is a short re-analysis of a small group with no data on broken bones, but it shows reassuring averages can hide worrying individual results.

Key findings

• The letter re-analysed individual bone scans from 24 teens in England's puberty blocker study (2011–15), part of a group of 31 described in an earlier 2019 paper.
• Over 2 years on puberty blockers, average bone density fell clearly behind other teens of the same age and sex, by roughly one 'step' on the standard scale at the hip and spine.
• After 2 years, about one in three patients had hip bone density low enough to count as abnormal, a level found in only 2.3% of teens of the same age and sex.
• More than a quarter had abnormally low spine bone density, and four were in the lowest 0.13% of the population (about 1 in 750).
• Allowing for the patients' height did not remove the group with very low scores.
• England's study originally excluded children whose bone density was already abnormally low. In 2012 this was relaxed to allow treatment 'in exceptional circumstances', despite the risk of brittle bones later in life.
• Biggs argues that broken bones should be recorded as side effects, and criticises proposals to scan bones less often or change the normal ranges for this group.

Conclusion

Biggs concludes that after 2 years of GnRHa, up to a third of patients had abnormally low bone density (Z-score below −2, the lowest 2.3% for sex and age), with a few in the lowest 0.13%. This undermines Joseph et al.'s reassuring conclusions. He calls their recommendations to reduce DXA monitoring and to redefine reference ranges for this cohort 'surprisingly complacent'. He argues that, rather than altering a measure that gives inconvenient findings, practitioners of puberty suppression must record fractures as adverse events. Whether cases of repeated fractures are exceptional is unknown because clinicians have not collected the relevant data.