FRI313 Clinical Implications Due To Long-term Delayed Diagnosis Of Macroprolactinemia

Disclosure: M. Antony: None. S. Gundlapally: None. M. Joglekar: None. B.N. Fritz: None. S. Patel: None. V. Verma: None. R. Kant: None. INTRODUCTION: The most common form of PRL (prolactin) in serum is known as monomeric prolactin and weighs 23kDa (kilo dalton) in size. However, prolactin can bind to IgG (immunoglobulin G) to weigh between 150 to 170 kDa. This form of prolactin is biologically inactive and is known as Macroprolactin. Studies have shown that Macroprolactin is responsible for 15 to 46% of cases of hyperprolactinemia. If it is not considered early during the work-up of persistent and asymptomatic hyperprolactinemia, it can lead to prolonged unnecessary work-up and/or treatment. We present a case of macroprolactinemia that was missed for many years leading to significant financial and psychological impact on the patient. CLINICAL CASE: 74-year-old Caucasian male was referred to our endocrinology clinic for further evaluation of chronic hyperprolactinemia. The first documented elevated serum PRL was 90 ng/ml (<20 ng/ml) in 1990.Patient did not recall the reason for checking PRL but recalled having no hypogonadal symptoms or headaches or visual changes. Repeat PRL was normal, and it stayed in range until 2007 when it was reported to be “high”. Other labs revealed normal TSH 1.93 uIU/ml (0.4-4.5 uIU/ml), normal total testosterone 532 ng/dl (264-916 ng/dl). MRI Brain with and without contrast in June 2007 was normal, and patient remained asymptomatic. Repeat PRL was normal, and it stayed in range until 2012 when it was elevated at 95 ng/ml with TSH 2.37 uIU/ml and total testosterone 554 ng/dl. MRI Brain in December 2012 was normal, and patient remained asymptomatic. Repeat PRL however continued to stay elevated since 2012 and ranged between 63.1 to 82.9 ng/ml. The TSH and total testosterone levels have stayed within the normal range. Patient was initially seen at our clinic in August 2022 and was clinically asymptomatic. He expressed a lot of frustration over the chronic diagnostic dilemma and was extremely worried if he indeed had a pituitary tumor that was previously missed on MRI. Pertinent lab results revealed normal ACTH 26.9 (7.2-63.3 pg/ml), low cortisol 4 mcg/dl (6-18 mcg/dl), normal IGF-1 135 (53-222 ng/ml), normal TSH 2.6 uIU/ml, normal Free T4 0.85 (0.8-1.8 ng/dl), elevated total serum PRL 36.8 ng/ml with normal monomeric PRL of 11.7 (4.04-15.2 ng/ml) and elevated macroprolactin percentage of 68%. Patient is currently being treated with hydrocortisone for secondary AI due to chronic prednisone use. CONCLUSION: Testing for Macroprolactin should be considered early in the workup of patients with persistent and asymptomatic hyperprolactinemia. This will not only help to avoid unnecessary testing and costs but will protect the psychological and emotional well-being of the patient. Our case serves as a good example of the benefit that could have been derived from early testing for macroprolactinemia. Presentation: Friday, June 16, 2023