The following is a summary of “Clinical Impact of New Reference Intervals for the Roche Prolactin II Immunoassay,” published in the June 2024 issue of Endocrinology by Earll, et al.

The Roche prolactin immunoassay is widely used globally but often yields higher values than the Siemens immunoassay despite similar manufacturer-defined reference intervals. This discrepancy can lead to diagnostic confusion when patient results fall above the Roche upper limit but within the Siemens interval. For a study, researchers sought to establish new reference intervals for both the Roche and Siemens prolactin immunoassays. 

They collected 374 specimens from healthy outpatients to establish these intervals. Additionally, we conducted a chart review for unnecessary testing and treatment among 298 patients with at least one Roche prolactin value above the manufacturer-defined upper limit but below our new upper limit.

The results revealed that the new upper limit for the Roche assay was determined to be 37.8 ng/mL for females and 22.8 ng/mL for males, while the manufacturer-defined limits were 23.3 ng/mL and 15.2 ng/mL, respectively. The new intervals for the Siemens assay were consistent with the manufacturer’s specifications. Importantly, no clinically significant pathophysiologic prolactin excess cases were identified in patients with values falling between the manufacturer-defined upper reference limit and our new Roche upper limit. Unnecessary further evaluation in these patients included repeat prolactin measurements, macroprolactin measurements, magnetic resonance imaging studies, and endocrine referrals. Additionally, some patients received dopamine agonists unnecessarily. The minimum cost of this excess care using Medicare reimbursement rates was calculated to be $34,134, with significantly higher amounts billed to patients and their insurance providers.

In conclusion, adopting new upper reference limits for the Roche prolactin assay of 37.8 ng/mL (females) and 22.8 ng/mL (males) would not delay diagnosis or necessary intervention in patients with clinically significant pituitary tumors. However, it significantly reduces unnecessary evaluations in patients without pathophysiologic prolactin excess, thus potentially reducing healthcare costs and patient burden.

Reference: academic.oup.com/jes/article/8/6/bvae069/7642642