Boys who are short due to underlying health problems are more likely than their female counterparts to be treated with growth hormone - but the gap is not explained by a bias in doctors’ recommendations for treatment, a new study suggests.

Growth hormone therapy may be prescribed to children with short stature due to certain medical causes, such as growth hormone deficiency, kidney disease and the side effects of brain radiation to treat cancer.

Research from various countries shows that about twice as many boys as girls are treated with growth hormone for these conditions. The reasons are unclear, but some have speculated that boys are more often referred for treatment because it is more socially acceptable for girls to be short.

A number of studies have supported this theory of “ascertainment bias.” A survey of U.S. pediatric endocrinologists, for example, found that when given a series of hypothetical patient scenarios, the doctors were 30 percent more likely to recommend boys for growth hormone treatment compared with girls.

Some other studies have found that at the time of referral for growth hormone treatment, girls tend to be significantly shorter than boys.

In the new study, Australian researchers found that among 1,485 children treated with growth hormone, the majority - 811 - were boys. In addition, boys outnumbered girls when it came to most individual indications for growth hormone therapy, including growth hormone deficiency, kidney failure and cranial radiation.

However, there was little evidence that girls were shorter than boys, on average, when referred for treatment. And among children with growth hormone deficiency or a history of radiation treatment, boys were typically shorter.

“What the findings suggest is that, in general, boys and girls who are eligible for growth hormone treatment have an equal chance of being identified and hence recommended for treatment,” lead researcher Dr. Ian P. Hughes told Reuters Health in an email.

“That is, there is no bias in the ascertainment of these children,” added Hughes, a research fellow at the University of Queensland.

The message for parents, he said, is that they can be “confident” that their sons and daughters have a comparable likelihood of having their short stature evaluated and, if appropriate, treated with growth hormone.

While the study was conducted in Australia, Hughes noted that the findings are likely applicable in other countries as well.

Ascertainment bias may play some role in the growth hormone gender gap, Hughes said, but it is probably a small one. Exactly what other factors are at work is not yet clear.

One possibility is that girls are more resistant to the growth effects of certain disorders.

“One way to look at it,” Hughes said, “is, boys and girls on average have the same set of genes but boys grow faster. Biological systems usually have some sort of a buffer before a threshold is reached and function is affected. If this is the case, girls have a bigger buffer; girls can sustain more mutations or other insults to the ‘growth system’ before their growth is compromised.”

It’s also possible that the criteria used to define “shortness” are playing a role.

Short stature in children is determined by how far a child deviates from the norm for his or her age and gender. To do that, doctors use growth charts developed by the U.S. Centers for Disease Control and Prevention (CDC), which are based on data collected on U.S. children from the 1960s through the early 1990s.

But, Hughes pointed out, it’s known that the average height in a population increases from one generation to the next. So the growth patterns among today’s kids are likely different from those of the children used to develop the CDC growth charts.

“If these changes between today’s population and the (CDC) population have occurred differently for boys and girls,” Hughes explained, “then our definition of shortness might now also be different between boys and girls, hence increasing the eligibility for growth hormone of one over the other.”

SOURCE: Journal of Clinical Endocrinology and Metabolism, online January 15, 2010.