Home > Treating Acromegaly > Diagnosing Acromegaly > Confirming the Diagnosis
Confirming the Diagnosis
Biochemical Testing
If it is suspected that a patient has acromegaly, a 2-step screening is recommended. Measurements of GH and/or IGF-1 levels can be taken to confirm the diagnosis.
GH Levels
GH levels are measured following overnight fasting. However, a single measurement of elevated GH does not confirm a diagnosis of acromegaly, because GH secretion from the pituitary occurs in spurts, and the concentration of GH in the blood may vary greatly at different times. In addition, a patient with acromegaly may have a normal GH level at any time.1
A more accurate measurement of GH can be obtained under conditions in which GH is normally suppressed. An oral glucose tolerance test (OGTT) is recommended to diagnose acromegaly. In healthy people, ingestion of 75 g of sugar glucose lowers the level of GH in the blood below 1 µg/L. This reduction does not occur in patients with acromegaly. According to the most recent consensus conference on acromegaly, an OGTT is the most reliable method for confirming a diagnosis of acromegaly.2,3
IGF-1 Levels
IGF-1 is a hormone that causes bone and tissue growth; it is produced in the liver under the influence of GH. IGF-1 signals the pituitary to reduce GH production. However, if GH production continues despite negative feedback mechanisms in the body, the level of IGF-1 in the blood will also increase, leading to bone growth and organ enlargement.1
IGF-1 levels are much more stable over the course of the day than GH levels, and elevation of this hormone almost always indicates the presence of acromegaly. However, some exceptions should be noted: the level of IGF-1 in the blood is 2 to 3 times higher than normal in pregnant women, can be abnormally low in people with poorly controlled diabetes, and is lower than normal in older people.1
Imaging Techniques
After confirmation of the diagnosis of acromegaly, imaging techniques (eg, CT or MRI scans) are used to locate the pituitary tumour causing GH overproduction. If a pituitary tumour cannot be located with these imaging studies, a nonpituitary tumour of the chest, abdomen, or pelvis may be the cause of GH overproduction. Measurement of GHRH, which stimulates the pituitary to make GH, along with CT scans of possible tumour sites, can be used to diagnose nonpituitary tumours.1
MRI scans of pituitary tumours causing acromegaly4:
- (a) Right-sided microadenoma, coronal section
- (b) Invasive macroadenoma extending into the cavernous sinus and suprasellar region, coronal section
- (c) Macroadenoma with suprasellar extension, sagittal section
Read more about effective management of acromegaly.
References: 1. National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, US Department of Health and Human Services. Acromegaly. Bethesda, MD: National Institutes of Health; 2008. NIH publication 08-3924. 2. Ben-Shlomo A, Melmed S. Acromegaly. Endocrinol Metab Clin North Am. 2001;30:565-583. 3. Melmed S. Medical progress: acromegaly. N Engl J Med. 2006;355:2558-2573. 4. Wass J, ed. Handbook of Acromegaly. Bristol, UK. BioScientifica; 2001:18-47.
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