The stability of C-peptide and insulin in plasma and serum samples under different storage conditions.
Author(s): Nkuna DX, Khoza SP, George JA, Maphayi MR
Publication: Clin Chem Lab Med, 2023, Vol. , Page
PubMed ID: 37409980 PubMed Review Paper? No
Purpose of Paper
This paper compared levels of c-peptide and insulin in serum and K2EDTA plasma from blood stored at room temperature for up to 72 h before centrifugation and in serum and K2EDTA plasma stored at room temperature for up to 48 h, 2-8°C for up to 7 days, and -20°C for up to 30 days.
Conclusion of Paper
Clinically and statistically significant declines in c-peptide levels in serum and K2EDTA plasma were noted when blood was stored at room temperature for 72 h pre-centrifugation (-74% and -46%, respectively) and when K2EDTA plasma or serum were stored at room temperature for 48 h (-29% and -31%, respectively). Insulin levels in serum and K2EDTA plasma declined when blood was stored at room temperature prior to centrifugation and when K2EDTA plasma or serum were stored at room temperature; however, clinically significant changes were limited to serum isolated from blood that was stored for ≥48 h prior to centrifugation and serum stored for ≥8 h at room temperature. When stored after separation, c-peptide levels were more stable in serum than K2EDTA plasma, and insulin was more stable in K2EDTA plasma than serum; however, only clinically insignificant declines in insulin and c-peptide levels were noted when either was stored at 2-8°C for ≤7 days or at -20°C for ≤30 days.
Studies
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Study Purpose
This study compared levels of c-peptide and insulin in serum and K2EDTA plasma from blood that was stored at room temperature for up to 72 h before centrifugation and in serum and plasma stored at room temperature for up to 48 h, 2-8°C for up to 7 days, and -20°C for up to 30 days. Blood was collected in syringes from five healthy volunteers after 8-10 h of fasting and from five healthy volunteers 30 min to 2 h after eating. Blood was then transferred to serum separator tubes (SST, three tubes with a volume of 5 mL and five tubes with a volume of 600 µL) and K2EDTA tubes (three tubes with a volume of 4 mL and five tubes with a volume of 500 µL). The 5 mL SST and 4 mL K2EDTA tubes were centrifuged within 1 h of collection at 3,500 rpm for 10 min to obtain serum and K2EDTA plasma, respectively, which were analyzed immediately and aliquoted for storage in Eppendorf tubes at -20°C for 72 h and 7, 21 and 30 days; in Hitachi cups at room temperature for 4, 8, 24, and 48 h; and in the refrigerator (2-8°C) for 24 h, 48 h, 5 days and 7 days. The 600 µL SST and 500 µL K2EDTA tubes were stored at room temperature for 1, 8, 12, 48, and 72 h before plasma/serum separation by centrifugation at 3500 rpm for 10 min. Levels of insulin and c-peptide were measured on the Roche Cobas e602 analyzer using electrochemiluminescent immunoassays. Clinical significance was defined as a change greater than the biological variation of ±36% for insulin and ±21% for c-peptide, which was derived from the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM) and the Westgard biological variation database, respectively.
Summary of Findings:
C-peptide levels in serum and K2EDTA plasma declined when blood specimens were stored prior to centrifugation at room temperature (P<0.001), with a decline from baseline (1 h) of -74% and -46% , respectively, after storage for 72 h. Similarly, the declines in c-peptide level was statistically and clinically significant when serum or K2EDTA plasma was stored at room temperature for 48 h (-29% and -31%, respectively, P<0.001 both). Slight and clinically insignificant declines in c-peptide occurred in both serum and K2EDTA plasma when stored at 2-8°C for 7 days (−6 % and −13 %) and when stored at -20°C for 30 days (<7%, both).
Insulin levels in serum and K2EDTA plasma declined rapidly when blood was stored prior to centrifugation at room temperature (P<0.001); however, only the decline in serum reached clinical significance (-66.67% after 48 h versus -23.37% in K2EDTA plasma after 72 h). Significant declines in insulin were observed following storage of either serum or K2EDTA plasma at room temperature (P<0.001, both); but, while clinically significant changes were first observed in serum levels after only 8 h (-38.40%), changes in K2EDTA plasms remained clinically insignificant after 48 h (-20.53%). Only small statistically and clinically insignificant changes in insulin were noted when serum or K2EDTA plasma were stored at 2-8°C for 7 days (18.85% and −10.14%, respectively) or -20°C for 30 days (-21.38% and 0.72%, respectively). The authors concluded that c-peptide was more stable in serum than K2EDTA plasma but that insulin was more stable in K2EDTA plasma than serum.
Biospecimens
Preservative Types
- Frozen
- None (Fresh)
Diagnoses:
- Normal
Platform:
Analyte Technology Platform Peptide Clinical chemistry/auto analyzer Pre-analytical Factors:
Classification Pre-analytical Factor Value(s) Biospecimen Aliquots and Components Centrifugation Centrifugation delays investigated
Storage Time at room temperature 1 h
8 h
48 h
72 h
12 h
Storage Storage duration 0, 4, 8, 24 and 48 h at room temperature
0, 1, 2, 5 and 7 days at 2-8°C
0, 3, 7, 21 and 30 days at -20°C
Storage Storage temperature Room temperature
2-8°C
-20°C
Biospecimen Aliquots and Components Blood and blood products Serum
Plasma
Whole blood