title: Prediction of Impending Type 1 Diabetes through Automated Dual-Label Measurement of Proinsulin:C-Peptide Ratio.
abstract: BACKGROUND
  The hyperglycemic clamp test, the gold standard of beta cell function, predicts impending type 1 diabetes in islet autoantibody-positive individuals, but the latter may benefit from less invasive function tests such as the proinsulin:C-peptide ratio (PI:C). The present study aims to optimize precision of PI:C measurements by automating a dual-label trefoil-type time-resolved fluorescence immunoassay (TT-TRFIA), and to compare its diagnostic performance for predicting type 1 diabetes with that of clamp-derived C-peptide release.
  
  
  METHODS
  Between-day imprecision (n = 20) and split-sample analysis (n = 95) were used to compare TT-TRFIA (AutoDelfia, Perkin-Elmer) with separate methods for proinsulin (in-house TRFIA) and C-peptide (Elecsys, Roche). High-risk multiple autoantibody-positive first-degree relatives (n = 49; age 5-39) were tested for fasting PI:C, HOMA2-IR and hyperglycemic clamp and followed for 20-57 months (interquartile range).
  
  
  RESULTS
  TT-TRFIA values for proinsulin, C-peptide and PI:C correlated significantly (r2 = 0.96-0.99; P<0.001) with results obtained with separate methods. TT-TRFIA achieved better between-day %CV for PI:C at three different levels (4.5-7.1 vs 6.7-9.5 for separate methods). In high-risk relatives fasting PI:C was significantly and inversely correlated (rs = -0.596; P<0.001) with first-phase C-peptide release during clamp (also with second phase release, only available for age 12-39 years; n = 31), but only after normalization for HOMA2-IR. In ROC- and Cox regression analysis, HOMA2-IR-corrected PI:C predicted 2-year progression to diabetes equally well as clamp-derived C-peptide release.
  
  
  CONCLUSIONS
  The reproducibility of PI:C benefits from the automated simultaneous determination of both hormones. HOMA2-IR-corrected PI:C may serve as a minimally invasive alternative to the more tedious hyperglycemic clamp test.
authors.affiliation: Diabetes Research Center, Brussels Free University-VUB, Brussels, Belgium.|Department of Clinical Chemistry and Radio-immunology, Universitair Ziekenhuis Brussel, Brussels, Belgium.
authors.forename: Annelien
authors.initials: A
authors.lastname: Van Dalem
authors.affiliation: Diabetes Research Center, Brussels Free University-VUB, Brussels, Belgium.|Department of Clinical Chemistry and Radio-immunology, Universitair Ziekenhuis Brussel, Brussels, Belgium.
authors.forename: Simke
authors.initials: S
authors.lastname: Demeester
authors.affiliation: Diabetes Research Center, Brussels Free University-VUB, Brussels, Belgium.
authors.forename: Eric V
authors.initials: EV
authors.lastname: Balti
authors.affiliation: Diabetes Research Center, Brussels Free University-VUB, Brussels, Belgium.|Department of Diabetology, Universitair Ziekenhuis Brussel, Brussels, Belgium.
authors.forename: Bart
authors.initials: B
authors.lastname: Keymeulen
authors.affiliation: Diabetes Research Center, Brussels Free University-VUB, Brussels, Belgium.|Department of Endocrinology, Universitair Ziekenhuis Leuven, Belgium.
authors.forename: Pieter
authors.initials: P
authors.lastname: Gillard
authors.affiliation: Department of Endocrinology, Universitair Ziekenhuis Gent, Ghent, Belgium.
authors.forename: Bruno
authors.initials: B
authors.lastname: Lapauw
authors.affiliation: Department of Endocrinology, Diabetology and Metabolism, Universitair Ziekenhuis Antwerpen, Edegem, Belgium.
authors.forename: Christophe
authors.initials: C
authors.lastname: De Block
authors.affiliation: Department of Endocrinology and Diabetology, GZA Campus Sint Augustinus en Sint Vincentius, Wilrijk-Antwerp, Belgium.
authors.forename: Pascale
authors.initials: P
authors.lastname: Abrams
authors.affiliation: Department of Endocrinology and Diabetology, Clinique du Sud Luxembourg et Clinique Saint Joseph, Arlon, Belgium.
authors.forename: Eric
authors.initials: E
authors.lastname: Weber
authors.affiliation: Diabetes Research Center, Brussels Free University-VUB, Brussels, Belgium.
authors.forename: Ilse
authors.initials: I
authors.lastname: Vermeulen
authors.affiliation: Diabetes Research Center, Brussels Free University-VUB, Brussels, Belgium.
authors.forename: Pieter
authors.initials: P
authors.lastname: De Pauw
authors.affiliation: Diabetes Research Center, Brussels Free University-VUB, Brussels, Belgium.
authors.forename: Daniël
authors.initials: D
authors.lastname: Pipeleers
authors.affiliation: Diabetes Research Center, Brussels Free University-VUB, Brussels, Belgium.|Department of Clinical Chemistry and Radio-immunology, Universitair Ziekenhuis Brussel, Brussels, Belgium.
authors.forename: Ilse
authors.initials: I
authors.lastname: Weets
authors.affiliation: Diabetes Research Center, Brussels Free University-VUB, Brussels, Belgium.|Department of Clinical Chemistry and Radio-immunology, Universitair Ziekenhuis Brussel, Brussels, Belgium.
authors.forename: Frans K
authors.initials: FK
authors.lastname: Gorus
mesh_terms: D000293:Adolescent; D000328:Adult; D001323:Autoantibodies / Q000097:blood; D002096:C-Peptide / Q000097:blood*; D002648:Child; D002675:Child, Preschool; D003922:Diabetes Mellitus, Type 1 / Q000097:blood* / Q000473:pathology; D005215:Fasting; D005260:Female; D005951:Glucose Tolerance Test; D006442:Glycated Hemoglobin / Q000378:metabolism; D006801:Humans; D006943:Hyperglycemia / Q000097:blood* / Q000473:pathology; D007328:Insulin / Q000097:blood; D007333:Insulin Resistance / Q000235:genetics; D050417:Insulin-Secreting Cells / Q000378:metabolism / Q000473:pathology; D008297:Male; D011379:Prognosis; D011384:Proinsulin / Q000097:blood*; D012044:Regression Analysis
chemical_list: D001323:Autoantibodies; D002096:C-Peptide; D006442:Glycated Hemoglobin; D007328:Insulin; D011384:Proinsulin; C517652:hemoglobin A1c protein, human