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[Macroprolactin detection: a new approach]
R Sapin1, F Gasser, E Fischbach
1Laboratoire universitaire de biophysique, Unité d'analyses endocriniennes, CNRS UPRES-A7004, Université Louis-Pasteur, Faculté de médecine, 67085 Strasbourg cedex.
Abstract:
Macroprolactin is a complex of prolactin with immunoglobulins (IgG) that has limited or no biological activity in vivo. Immunoassays for prolactin have variable reactivity with macroprolactin. Therefore the presence of macroprolactin should be considered in the differential diagnosis of hyperprolactinemia. We compared a valid screening test for macroprolactin, polyethyleneglycol (PEG) precipitation, with the determination of the ratio of the results of two prolactin assays: Elecsys with high cross-reactivity with macroprolactin and Centaur with low cross-reactivity. In 59 negative samples subjected to the PEG test (precipitation < 50%), the Elecsys/Centaur ratio ranged between 1.11 and 1.45. Among 35 positive samples (precipitation > 60%), 33 had, as expected, an increased ratio (over 1.45), 1 a normal ratio and 1 a decreased ratio (1.07). This decreased ratio could be due to a particular form of macroprolactin poorly recognised by the Elecsys assay. Among 5 samples in the grey zone (precipitation between 50 and 60%), the ratio was increased in 2, normal in 1 and decreased in 2. Apart from one false negative case (normal ratio with positive PEG test), the results of the Elecsys/Centaur ratio method were in good agreement with those of the PEG test. The ratio method could be helpful for samples with PEG test results in the grey zone, before undertaking a complete analysis of circulating molecular forms by gel filtration chromatography. Out of the 5 five samples in the grey zone, the ratio was 4 times out of the reference range: 2 increased, 2 decreased. Our results also underline the necessity of reevaluating the Centaur prolactin reference range from samples without macroprolactin.
Insights
Macroprolactin, a prolactin-immunoglobulin complex, can interfere with hyperprolactinemia diagnosis. A two-assay ratio method shows good agreement with PEG precipitation for detecting macroprolactin, aiding clinical assessment.
Area of Science:
- Clinical Chemistry
- Endocrinology
- Laboratory Medicine
Background:
- Macroprolactin, a complex of prolactin with immunoglobulins (IgG), exhibits limited biological activity.
- Immunoassays for prolactin demonstrate variable reactivity with macroprolactin, complicating hyperprolactinemia diagnosis.
- Macroprolactin should be considered in the differential diagnosis of elevated prolactin levels.
Purpose of the Study:
- To compare polyethyleneglycol (PEG) precipitation, a screening test for macroprolactin, with a novel ratio method using two prolactin assays.
- To evaluate the utility of the Elecsys/Centaur prolactin assay ratio in identifying macroprolactin compared to PEG precipitation.
- To assess the agreement between the PEG test and the assay ratio method for macroprolactin detection.
Main Methods:
- Comparison of PEG precipitation test results with the ratio of prolactin measurements from Elecsys (high macroprolactin reactivity) and Centaur (low macroprolactin reactivity) assays.
- Analysis of 59 PEG-negative, 35 PEG-positive, and 5 PEG-grey zone samples.
- Evaluation of the Elecsys/Centaur ratio in relation to PEG precipitation results.
Main Results:
- The Elecsys/Centaur ratio showed good agreement with the PEG test, correctly identifying most macroprolactin-positive and negative samples.
- Among PEG-positive samples, 33 out of 35 showed an increased ratio (>1.45).
- In the PEG-grey zone, the ratio method provided additional discriminatory information, with 4 out of 5 samples showing ratios outside the reference range.
Conclusions:
- The Elecsys/Centaur prolactin assay ratio is a valuable method for detecting macroprolactin, complementing PEG precipitation.
- The ratio method is particularly useful for samples with equivocal PEG test results.
- Reevaluation of the Centaur prolactin reference range using samples without macroprolactin is recommended.