Stability and reproducibility of a single-sample urinary C-peptide/creatinine ratio and its correlation with 24-h urinary C-peptide.

Author(s): McDonald TJ, Knight BA, Shields BM, Bowman P, Salzmann MB, Hattersley AT

Publication: Clin Chem, 2009, Vol. 55, Page 2035-9

PubMed ID: 19713273 PubMed Review Paper? No

Purpose of Paper

Conclusion of Paper

Studies

1. Study Purpose

   The purpose of this study was to investigate the effects of different storage conditions and preservatives on urinary C-peptide/creatinine ratio (UCPCR) from first and second morning voids and 24-h collections.

   Summary of Findings:

   UCPCR levels remained stable, regardless of preservative, at 4 degrees C for 72 hours. At 21 degrees C, UCPCR levels were stable for 24 hours without preservation and for 72 h if boric acid or sodium carbonate were added. In specimens preserved with sodium azide, storage at 21 degrees C for 72 h decreased UCPCR by 8% compared to baseline, whereas no preservation led to a 31% decrease. Storage at -20 degrees C for 90 days decreased UCPCR levels by 16-18% compared to baseline, but up to 7 freeze-thaw cycles had no effect on UCPCR. Second-void fasting UCPCRs showed less variability and were lower than first-void fasting UCPCRs, and additionally showed a high correlation with 24-h urinary C-peptide concentrations.

   Biospecimens

   • Bodily Fluid - Urine

   Preservative Types

   • None (Fresh)
   • Other Preservative

   Diagnoses:

   • Normal

   Platform:

   Analyte	Technology Platform
   Peptide	Clinical chemistry/auto analyzer
   Small molecule	Clinical chemistry/auto analyzer

   Pre-analytical Factors:

   Classification	Pre-analytical Factor	Value(s)
   Storage	Storage temperature	21 degrees C 4 degrees C -20 degrees C
   Storage	Storage duration	12 h 24 h 48 h 72 h 3 months
   Storage	Freeze/thaw cycling	0 cycles 1 cycle 2 cycles 3 cycles 4 cycles 5 cycles 6 cycles 7 cycles
   Biospecimen Aliquots and Components	Aliquot sequential collection	1st collection 2nd collection 24 hour collection
   Biospecimen Preservation	Type of fixation/preservation	None (fresh) Boric acid Sodium azide Sodium carbonate

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