Laboratory and clinical experience in 55 patients with macroprolactinemia identified by a simple polyethylene glycol precipitation method

PRL exists in different forms in human serum. The predominant form is littl e PRL (molecular mass 23 kDa) with smaller amounts of big PRL (molecular ma ss 50-60 kDa) and at times big big or macroprolactin (molecular mass 150-17 0 kDa). The frequency and clinical consequences of macroprolactinemia have not been clearly established, mainly because of difficulty in identifying t hese patients biochemically. This previously required the use of gel filtra tion chromatography, which could not be used routinely. Recently, a screeni ng test using polyethylene glycol (PEG) has been used to identify macroprol actin in serum. Consequently, this study was designed to examine the use of PEG precipitation in the identification of patients with a predominance of macroprolactin and to establish the clinical characteristics of such a coh ort. Over 12 months, 18,258 requests for serum PRL were received and of these 12 25 patients had a serum PRL more than 700 mU/L. A total of 322 of these pat ients (26%) had a percentage recovery after PEG precipitation of less than 40%, thus indicating the presence of a predominance of macroprolactin. Fifty-five of these patients were referred for detailed clinical assessment . Symptoms typical of hyperprolactinemia were not common in this cohort. No ne had sustained amenorrhea and eight have had oligomenorrhea at age less t han 40 yr. One had galactorrhea. All had pituitary imaging, and four had a microadenoma with none having a macroadenoma. PEG precipitation allows easy identification of macroprolactin in routine c linical practice. As the clinical consequences of this entity at this stage seem relatively benign, referral and intensive investigation of these pati ents may not be necessary. However, follow-up of a large cohort is required to ensure that the long-term outlook is likewise benign. This would have i mportant implications for both patients and healthcare systems.