Clinical Impact of New Reference Intervals for the Roche Prolactin II Immunoassay

Area of Science:

• Clinical Chemistry
• Endocrinology
• Laboratory Medicine

Background:

• The Roche prolactin immunoassay often reports higher values than the Siemens assay, despite similar manufacturer-defined reference intervals.
• This discrepancy causes diagnostic confusion, with patient results frequently exceeding Roche's upper limit but remaining within Siemens' range.

Purpose of the Study:

• To establish new, accurate reference intervals for both Roche and Siemens prolactin immunoassays.
• To evaluate the impact of revised Roche assay intervals on diagnostic practices and patient care.

Main Methods:

• New reference intervals were established using 374 specimens from healthy outpatients.
• A chart review assessed unnecessary testing and treatment in 298 patients with Roche prolactin values above the manufacturer's upper limit but below the newly established limit.

Main Results:

• New upper limits for the Roche assay were determined as 37.8 ng/mL (females) and 22.8 ng/mL (males), significantly higher than manufacturer limits (23.3 ng/mL and 15.2 ng/mL).
• Siemens assay intervals matched manufacturer recommendations. No clinically significant prolactin excess was found in patients between the old Roche limit and the new one.
• Unnecessary evaluations included 459 repeat tests, 57 macroprolactin tests, 39 MRIs, 28 endocrine referrals, and 11 patients treated with dopamine agonists, costing at least $34,134 in excess care.

Conclusions:

• Adopting the new Roche prolactin assay upper limits (37.8 ng/mL females, 22.8 ng/mL males) would not impede diagnosis of significant pituitary tumors.
• Implementing these revised limits would substantially decrease unnecessary patient evaluations and associated healthcare costs for individuals without pathophysiologic prolactin excess.