medwireNews: Clinicians should monitor growth hormone (GH) levels in children between intravenous (iv) line placement and initiation of insulin tolerance test (ITT), to guard against the confounding effects of a stress response, say researchers.

The team identified a group of children who had marked increases in GH levels after iv line placement, but did not have a similar response to the subsequent ITT.

Therefore, delays in GH measurement after iv line placement “may increase the number of patients misclassified as having insufficient GH secretion”, Colin Hawkes (The Children’s Hospital of Philadelphia, Pennsylvania, USA) and study co-authors write in The Journal of Clinical Endocrinology & Metabolism.

Among 97 children who underwent evaluation at a centre in Dublin, Ireland, 13 had a peak GH level exceeding 7 ng/mL within 30 minutes of iv line placement, but did not reproduce this response on administration of insulin. Overall, there was only a weak correlation between the peak GH level after iv line placement and after ITT.

Eleven children had no response to iv line placement, but reacted to the ITT, three children had a response to both stimuli and the other 70 did not respond to either and were considered GH deficient.

The researchers say that previous research has shown the potential for attenuated GH responses to sequential stimuli, and suggest that the initial stimulus could reduce reserves of “immediately releasable pituitary GH”.

The study cohort included 76 children who were undergoing initial evaluation, at an average age of 10.9 years. Accounting for the response to iv line placement in these children increased the proportion passing the GH stimulation test from 10.5% to 25.0%. Among 21 children undergoing testing at transition to adulthood, it increased the proportion from 28.6% to 38.1%.

In the initial evaluation group, GH levels of the 11 children with a response to iv line placement only exceeded 7 ng/mL at the time of placement in three children, after 15 minutes in five, and after 30 minutes in five children, with one having elevated GH levels at all three timepoints.

The researchers note that many centres perform a repeat stimulation test, which may detect some of the children whose response to iv line placement confounded their ITT response in the first test.

Nevertheless, the team advises frequent additional GH measurements if ITT is performed immediately after iv line placement, and regular monitoring of levels after placement if ITT is delayed.

By Eleanor McDermid, Senior medwireNews Reporter

J Clin Endocrinol Metab 2015; Advance online publication

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