From Michigan, USA:
I have type 1 diabetes, and my two year old son has been diagnosed with a potential growth hormone deficiency, and he is being sent to a pediatric endocrinologist at the nearby medical school. His somatomedin-C level was 15 ng/dl (I'm not sure of the units), and I saw what his pediatrician was not sure of because the normals in children ages 1-4 were expressed in different units which did not match my son's value. So, his pediatrician was not sure if his level was a cause of concern since all other labs were normal. At the time of the test, my son was getting over a cold and had no fever.
I am worried and did not know what to do. I am hoping that you could help put my mind at rest, or at least let me know what we are in for. Could you explain these levels and what types of tests would be run to check this out? Could any of this have anything to do with my diabetes or use of insulin during my pregnancy? How often should these tests be performed? If there is a deficiency when, or at what age, should growth hormone replacement be started? Is it possible that a child have a low somatomedin-C level due to genetics, possibly due to short stature naturally?
IGF-1 (or somatomedin-C) is a screening test for growth hormone deficiency. Growth hormone tells the liver to make IGF-I. Unfortunately, values are so low in two year olds that it can sometimes be difficult to tell the difference between a normal value and a low value. There is no perfect test for growth hormone deficiency that doesn't have both false normal values and false low values. Growth hormone goes up and down during the day, mainly up at during sleep at this age.
The usual tests try to do something artificial to make growth hormone go up. There are many different "stimulation" tests that can be done to try and stimulate the growth hormone with different drugs. Every endocrinologist has his/her own favorite tests. Personally, at this age, when possible, I like to draw blood for cortisol and growth hormone when the child either has a fever over 101 degrees and or is vomiting if I do not feel it is urgent to make the diagnosis. These are natural stimuli of growth hormone and cortisol secretion, and an elevated level when sick at least lets you know that the child can make these hormones when he needs to. Of course, that still doesn't mean his own spontaneous secretion is normal. You can even draw blood every 20 minutes during the night to see if growth hormone goes up, but there are no good normals for this. For slightly older children, I have them exercise fasting for 20 minutes. 75% of healthy children make growth hormone in this setting, but it is hard to get a two year old to exercise steadily for 20 minutes (I usually can get three year olds to jump on a rebounder and chase me around the building!). If a child passes any of these simple blood tests, there is no need to go on to more formal, expensive, time consuming tests where you draw blood every 15-30 minutes for 90 minutes to three hours after giving a drug that makes growth hormone go up. Even if your son passes all the tests, if he really isn't growing well and you have ruled out all other medical conditions, he still may be a candidate for growth hormone treatment.
As far as I know, infants of mothers with diabetes are not more at risk of having growth hormone deficiency, but they are at increased risk of thyroid problems, celiac disease, and possibly inflammatory bowel disease all of which can present with just growth failure initially before they cause other, more specific symptoms.
Your specific questions are too complicated to answer and must be answered by the doctor treating your son. If a child fails one growth hormone test, it is usually traditional to do at least another one. Other tests may just be done once depending on results, while thyroid might be repeated periodically.
Additional comments from Dr. David Schwartz:If I am interpreting this correctly, your son is now about two years old and apparently not growing the way people think he ought to, which prompted the IGF-1 level, and you have type 1 diabetes. Right? Okay. The child's growth has little to do with the mother's diabetes, assuming she was in good control, especially given a normal birth weight and length.
Children not uncommonly "cross percentiles" (up or down) of the growth charts between the ages of 6-18 months. I agree that since your son is below the curve (I assume that is what is meant by "0%"), he warrants watching. It is important to know if the doctor was monitoring this child's length or height and plotting on the appropriate growth chart when the "fall off" was noted. We are all "longer than tall" so if a height is measured, and plotted on a length growth chart, the child will appear to have "fallen off."
Additional comments from Dr. Larry Deeb:The best advice is to see the endocrinologist. I must confess, that's why doctors shouldn't do tests they can't interpret. IGF-1 has a very wide standard deviation at this age and does rise as a child ages. It is maximum during the middle of puberty, but 15 is still low for a two year old.. More importantly, what is his growth pattern, etc.?
Original posting 2 Dec 2001
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