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Dried Blood Spot Assay of Insulin-Like Growth Factor (IGF)-I and IGF Binding Protein-3 (IGFBP-3)—Authors’ Response

Diagnostic Systems Laboratories (Canada) Inc. University of Toronto Toronto, Ontario, Canada

Anastasia Diamandi

Diagnostic Systems Laboratories (Canada) Inc. Toronto, Ontario, Canada

We regret that our recent publication of the IGF-I/IGFBP-3 dried blood spot assays, which appeared in the July issue of this journal (1), did not include a previously published filter paper dried blood spot IGF-I radioimmunoassay by Mitchell, Hermos, and Moses (2). We would like, however, to offer our sincere thanks to Drs. Mitchell, Hermos, and Moses for their interest in our paper and for providing us the opportunity to further discuss a number of differentiating features of the technology we published.

As outlined (1), the major emphasis of our work has been development of a highly efficient procedure for complete extraction of IGF-I/IGFBP-3 from dried blood filter paper spots, which could include any analyte-specific sample pretreatment, such as acidification, to dissociate IGF complexes, that may be needed for optimal performance. In this approach, the extraction protocol is totally independent of the assay methodology, allowing immediate or subsequent analysis of the extract for components of interest by the available immunoassay kits developed for serum/plasma determinations. We specifically investigated development of procedures that would not combine the extraction as well as the analytical step into a single-step procedure, thus avoiding the simultaneous incubation of the dried blood spot disc with the relevant antibody and the labeled tracer as developed for IGF-I by Mitchell et al. (2). Our demonstrations of IGF-I/IGFBP-3 distribution in the plasma fraction of the whole blood and the minimal effect of hematocrit changes on dried blood spot IGF-I/IGFBP-3 determinations further allowed the use of buffer-based standards which, relative to the traditional dried blood spot standards (2), have the important advantages of simplified formulation and improved assay consistency.

In addition to the reported applications (1), our approach was primarily designed for universal applicability to dried blood spot determinations of other components of the IGF system. In fact, the initial submission of our paper included specific reference to the successful adaptation of the technology to dried blood spot assay of IGF-II, IGFBP-1, IGFBP-2, and ALS. The reference to these applications was subsequently removed from the revised version based on the recommendation of the reviewers. However, as noted in our paper (1), we broadly acknowledged previous application of the dried blood spot technology in other medical disciplines (3, 4, 5, 6, 7, 8), and we fully agree with Drs. Mitchell, Hermos, and Moses on the significant potentials and advantages of the dried blood spot determinations, as indicated in their above letter to the editor.

Footnotes

Received November 12, 1998. Address correspondence to: M. Javad Khosravi, Diagnostic Systems Laboratories (Canada) Inc., Mount Sinai Hospital, Room 653, 600 University Avenue, Toronto, Ontario M5G 1X5, Canada.

References

1. Diamandi A, Khosravi MJ, Mistry J, Martinez V, Guevara-Aguirro J. 1998 Filter paper blood spot assay of human insulin-like growth factor I (IGF-I) and IGF binding protein-3 and preliminary application in the evaluation of growth hormone status. J Clin Endocrinol Metab. 83:2296–2301.[Abstract/Free Full Text]
2. Mitchell ML, Hermos RJ, Moses AC. 1987 Radioimmunoassay of somatomedin-C in filter paper discs containing dried blood. Clin Chem. 33:536–538.[Abstract/Free Full Text]
3. Dussault JH, Coulombe P, Laberge C. 1974 Preliminary report on a mass screening program for neonatal hypothyroidism. J Pediatr. 86:670–674.
4. Augier D, Sarramon MF, Rorive C, et al. 1985 Results of an experiment in systematic prenatal screening for neural tube malformations by assay of alpha fetoproteins in dried blood samples. J Genet Hum. 33:325–336.[Medline]
5. Chanteau S, Plichart R, Boutin JP, Roux J, Cartel JL. 1989 Finger-prick blood collection and computer-assisted enzyme-linked immunosorbent assay for large scale serological studies on leprosy. Trans R Soc Trop Med Hyg. 83:414–416.[CrossRef][Medline]
6. Hoxic NJ, Vergeront JM, Pfister JR, Hoffman GL, Markwardt-Elmer PA, Davis JP. 1992 Improving estimates of HIV-I seroprevalence among childbearing women using smaller blood spots. Am J Public Health. 82:1370–1373.[Abstract/Free Full Text]
7. Missler U, Gutckunst R, Wood WG. 1994 Thyroglobulin is a more sensitive indicator of iodine deficiency than thyrotropin. Development and evaluation of dry blood spot assays for thyrotropin and thyroglobulin in iodine-deficient geographical areas. Eur J Clin Chem Clin Biochem. 32:137–143.[Medline]
8. Hoffman BR, Yu H, Diamandis EP. 1996 Assay of prostate-specific antigen from whole blood spotted on filter paper and application to prostate cancer screening. Clin Chem. 42:536–544.[Abstract/Free Full Text]

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