Acromegaly has a slow course and symptoms often take months or even years to develop. If the condition is suspected, diagnostic tests are prescribed. The tests are outlined as follows.
Blood tests are prescribed to detect the levels of growth hormone in the body. In persons with Acromegaly the levels of growth hormone is elevated.
For diagnosis, a single measurement of an elevated blood level of growth hormone is not enough. This is because normally this hormone is secreted by the pituitary in impulses or spurts and has several spikes and waves that may change the concentration in the blood from minute to minute. Thus those with Acromegaly may have normal levels of growth hormone at one point in time and someone who has normal pituitary function may have a level several times higher at the same point in time.
Thus to get an accurate idea about abnormal levels of growth hormone secretion the person is subjected to test conditions. Health care professionals often use the oral glucose tolerance test to diagnose Acromegaly.
In a normal person drinking 75 to 100 grams of glucose solution lowers blood levels of growth hormone to less than 1 nanogram per millilitre (ng/ml). In those with Acromegaly and growth hormone overproduction this suppression does not occur. Thus the oral glucose tolerance test is a reliable method for confirming a diagnosis of Acromegaly.
Tests are also prescribed to measure blood levels of Insulin-like growth factor 1 (IGF-1). This level rises as the levels of growth hormone rises. Because IGF-I levels are much more stable than growth hormone throughout the day, screening for Acromegaly with IGF-1 levels is a more reliable method.
Elevated IGF-I levels almost always indicate Acromegaly. It must be remembered however that pregnancy causes a physiological rise in IGF-1 by two to three times and with age the IGF-1 levels decline. Levels may be low in persons with poorly controlled diabetes or liver or kidney disease.
IGF-binding protein-3 (IGFBP-3) is a protein that binds to circulating IGF in the body. When levels of IGF-1 are raised this protein levels also rises. This can be used in diagnosis of Acromegaly. Growth hormone-releasing hormone (GHRH) concentration can be estimated.
With involvement of the pituitary gland, other hormones may be affected. Assessment of these hormones including prolactin, adrenal, thyroid, and gonadal hormones may help detect abnormalities.
In addition, blood glucose, serum phosphate, and serum triglycerides may also be raised. Urine examination may reveal raised urinary calcium levels.
After blood levels are found to be indicative of Acromegaly, imaging studies are prescribed. A magnetic resonance imaging (MRI) scan of the brain and pituitary gland especially is the first choice of investigation. This helps in detection of the location and size of the tumor.
MRI is the most sensitive imaging technique but as an alternative computerized tomography (CT) scans can be used.
In patients who have nonpituitary tumors elsewhere which are secreting growth hormone or Growth hormone releasing hormone (GHRH) a CT scan or a whole body MRI scan may be prescribed.
Total body scintigraphy with radio-labelled OctreoScan® (somatostatin) is prescribed in some patients for detection of these non-pituitary tumors.
Visual field tests
Visual field tests are conducted to see the extent of damage to the optic chiasma and the optic nerves.
Electrocardiogram and echocardiogram
Patients are screened for heart disease with Electrocardiogram and echocardiogram. Since there is a high risk of colon cancers and colonic polyps among Acromegaly patients, an assessment of the same is indicated.
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)