PMON117 IGF-1 Testing: Diagnostic Pitfalls

Abstract

Abstract Introduction Acromegaly is a rare endocrine disorder, with an incidence of 5.3/million/year, that results from persistent hypersecretion of growth hormone (GH), which stimulates hepatic secretion of insulin-like growth factor-1 (IGF-1). The best single test for the diagnosis of acromegaly is measurement of serum IGF-1; however, the result must be interpreted with caution, with understanding of potential pitfalls. Here we present a case of falsely elevated IGF-1 levels. Case Description A 43-year-old female with medical history of prediabetes, sleep apnea, and headaches was referred to endocrine clinic for evaluation of possible acromegaly. Patient had been evaluated by her primary care physician for frequent headaches, unintentional weight gain, and bilateral leg and hand swelling. Patient endorsed being unable to wear her wedding ring for a few years. Initial laboratory evaluation by primary care physician 3 months prior revealed normal thyroid function, prolactin, FSH, LH, random cortisol, but elevated IGF-1 of 310 ng/mL (normal 71-258 ng/mL), with negative pregnancy test. Brain MRI at that time revealed a pineal gland cyst but no pituitary abnormality. During her initial endocrine visit, IGF-1 was repeated, which was again elevated but improved to 283 ng/mL (normal 71-258 ng/mL). Other pertinent labs included a normal random ACTH of 18 pg/mL (normal <47 pg/mL), and pm cortisol of 2.4 mcg/dL (normal 2.9-17.3 mcg/dL). Physical examination was notable for a few light purple striae on abdomen, acanthosis nigricans, and mild limb edema, but no macrognathia, enlarged hands or feet. Given patient's lack of typical features of acromegaly, normal pituitary imaging, and spontaneous IGF-1 improvement, it was decided to postpone GH measurements with oral glucose tolerance test but repeat IGF-1 in 6 months. Patient was able to follow up 11 months after initial visit at which patient denied any worsening symptoms. At that time, repeat laboratory study showed normal IGF-1 of 231. Given spontaneous normalization of IGF-1 levels, no further laboratory testing or imaging studies were recommended, and patient was instructed to follow up in 11-12 months. Discussion Prompt diagnosis of acromegaly is crucial. However, it is important to note IGF-1 could be falsely elevated. A retrospective review by Erickson et. al of 2747 unique patients with IGF-1 elevation, 117 (4%) were found to have false-positive results following a review of the clinical data. In addition to acromegaly, other causes of elevated IGF-1 levels include high protein and high glycemic-index diet, pregnancy, hyperthyroidism, IGF-1 assay problems, and some rare tumors (carcinoids) secreting IGF-1. Discovery of "falsely" elevated IGF-1 may lead to unnecessary testing and physician visits. Therefore, clinicians should consider retesting patients after some time interval if spurious IGF-1 is suspected, before aggressively pursuing more extensive investigations. Presentation: No date and time listed