Clinical Chemistry
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Clinical Chemistry 49: 2104-2105, 2003; 10.1373/clinchem.2003.024992
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(Clinical Chemistry. 2003;49:2104-2105.)
© 2003 American Association for Clinical Chemistry, Inc.

Letters to the Editor

"MacroLH": Anomalous Molecular Form That Behaves as a Complex of Luteinizing Hormone (LH) and IgG in a Patient with Unexpectedly High LH Values

José Gilberto Henriques Vieira1,a, Sônia Kiiomi Nishida1, Maria Teresa Faria de Camargo1, Omar Magid Hauache1, Rui Monteiro de Barros Maciel1 and Valéria Guimarães2

1 Laboratório Fleury, 04344-070 São Paulo, SP, Brazil
2 Endocrinologia e Nefrologia, 70373-050 Brasília, DF, Brazil

aAuthor for correspondence. Fax 55-11-5014-7425; e-mail jose.vieira{at}fleury.com.br.


To the Editor

Interference in immunoassays from endogenous antibodies directed against peptide hormones is a well-documented phenomenon. It is known to occur for insulin, growth hormone, and especially prolactin, being responsible for most cases of "macroprolactin" (1)(2)(3). However, interference is rare in assays for pituitary glycoprotein hormones, being described only for thyroid-stimulating hormone (4)(5). To date, it has not been described for luteinizing hormone (LH).

We present the case of a female patient, 23 years of age, with a diagnosis of congenital adrenal hyperplasia (late-onset 21-hydroxylase defect) and Hashimoto thyroiditis, both conditions under treatment. The laboratory evaluation showed a high LH value (206.0 IU/L) with follicle-stimulating hormone (4.0 IU/L), estradiol (66 ng/L), and prolactin (10 µg/L) values within the appropriate reference intervals. Serum human chorionic gonadotropin was undetectable (<2 IU/L), and the thyroid-stimulating hormone (1.0 mIU/L) and {alpha}-subunit concentrations (553 ng/L; reference interval, 80–604 ng/L) were within the appropriate reference intervals. Antibodies against thyroperoxidase were present in high concentrations (1400 kU/L; reference values <40 kU/L). The patient was not using any LH-stimulating drug, nor had she ever received LH or human chorionic gonadotropin injections.

LH was measured by an immunofluorometric assay (in house), and the values were confirmed by an electrochemiluminescent assay (Roche). Serial dilution showed parallelism with the curve obtained with a standard LH preparation. Her serum was subjected to gel-filtration chromatography on a Superdex 200 column (1.5 x 30 cm; Pharmacia) calibrated with the Pharmacia high-molecular-weight calibrators, and the elution profile showed that almost all of the LH eluted as a high-molecular-weight form (Mr >250 000; Fig. 1 ). Recovery after precipitation with polyethylene glycol (6) was only 7% compared with a mean recovery of 87.5% (range, 56–108%) obtained for 23 sera from female patients with LH values >40 IU/L. Serum application to a protein G-Sepharose column (Pharmacia) showed complete binding of the LH immunoreactivity, which was eluted by lowering the pH to 2.8. Gel filtration in dissociating conditions (0.1 mol/L glycine-HCl, pH 2.8) shifted the LH peak to the expected molecular size.



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  		Figure 1. Elution profiles for sera from a healthy menopausal patient ({circ}) and from the study patient (•).

The sera were chromatographed on a 1.5 x 30 cm Superdex 200 column. V0, void volume.

What called our attention to this case, and prompted additional studies, were the unexpectedly high LH values, with concomitant FSH and estradiol values within the appropriate reference intervals. The etiology and frequency of the phenomenon as well as its relationship with autoimmune diseases remains to be defined. Nevertheless, this new possibility must be considered in the event of a finding of unexpectedly high LH values.


References

  1. Cavaco B, Leite V, Santos AM, Arranhado E, Sobrinho LG. Some forms of big-big prolactin behave as complex of monomeric prolactin with an immunoglobulin G in patients with macroprolactin or prolactinoma. J Clin Endocrinol Metab 1995;80:2342-2346.[Abstract]
  2. Bjoro I, Morkrid K, Wereland R, Turter A, Kvistborg A, Sand T, et al. Frequency of hyperprolactinemia due to large molecular weight prolactin (150–170 kDa PRL). Scand J Clin Invest 1995;55:139-147.[Web of Science][Medline] [Order article via Infotrieve]
  3. Fahie-Wilson MN, Soule SG. Macroprolactinemia: contribution to hyperprolactinemia in a district general hospital and evaluation of a screening test based upon precipitation with polyethylene glycol. Ann Clin Biochem 1997;34:252-258.
  4. Bifulco M, Spitz I, Hirch HJ, Shorer Z, Aloj SM. High molecular-weight serum thyrotropin revisited. N Engl J Med 1987;316:1609-1610.[Medline] [Order article via Infotrieve]
  5. Sapin R, d’Herbomez M, Schlienger JL, Wemeau JL. Anti-thyrotropin antibody interference in thyrotropin assays. Clin Chem 1998;44:2557-2559.[Free Full Text]
  6. Vieira JGH, Tachibana TT, Obara LH, Maciel RMB. Extensive experience and validation of polyethylene glycol precipitation as a screening method for macroprolactinemia. Clin Chem 1998;44:1758-1759.[Free Full Text]



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