Interlaboratory Comparison of Antibody-Free LC-MS/MS Measurements of C-peptide and Insulin.

BACKGROUND: The enhanced precision and selectivity of liquid chromatography-tandem mass spectrometry (LC-MS/MS) makes it an attractive alternative to certain clinical immunoassays. Easily transferrable work flows could help facilitate harmonization and ensure high-quality patient care. We aimed to evaluate the interlaboratory comparability of antibody-free multiplexed insulin and C-peptide LC-MS/MS measurements. METHODS: The laboratories that comprise the Targeted Mass Spectrometry Assays for Diabetes and Obesity Research (TaMADOR) consortium verified the performance of a validated peptide-based assay (reproducibility, linearity, and lower limit of the measuring interval [LLMI]). An interlaboratory comparison study was then performed using shared calibrators, de-identified leftover laboratory samples, and reference materials. RESULTS: During verification, the measurements were precise (2.7% to 3.7%CV), linear (4 to 15 ng/mL for C-peptide and 2 to 14 ng/mL for insulin), and sensitive (LLMI of 0.04 to 0.10 ng/mL for C-peptide and 0.03 ng/mL for insulin). Median imprecision across the 3 laboratories was 13.4% (inter-quartile range [IQR] 11.6%) for C-peptide and 22.2% (IQR 20.9%) for insulin using individual measurements, and 10.8% (IQR 8.7%) and 15.3% (IQR 14.9%) for C-peptide and insulin, respectively, when replicate measurements were averaged. Method comparison with the University of Missouri reference method for C-peptide demonstrated a robust linear correlation with a slope of 1.044 and r2 = 0.99. CONCLUSIONS: Our results suggest that combined LC-MS/MS measurements of C-peptide and insulin are robust and adaptable and that standardization with a reference measurement procedure could allow accurate and precise measurements across sites, which could be important to diabetes research and help patient care in the future.

Insights into insulin analog cross-reactivity: a comparative study of Siemens Atellica and LC-MS/MS.

BACKGROUND: To address the challenges posed by inconsistent detection of analog insulin in commercially available insulin immunoassays, resulting in potential discrepancies in clinical findings and misdiagnosis during the investigation of factitious hypoglycemia., we aimed to evaluate the ability of the Siemens Atellica automated immunoassay to detect insulin analogs compared with LC-MS/MS. METHODS: Five insulin analogs were analyzed at 10 ng/mL spiked into serum samples, with recombinant human insulin as positive controls. Insulin and C-peptide assays were performed using Siemens Atellica and LC-MS/MS. Recovery rates were calculated. RESULTS: Siemens Atellica immunoassay demonstrated robust cross-reactivity (92-121%) of insulin analogs. In contrast, glargine was detected by LC-MS/MS but other analogs were not observed (<10% recovery). CONCLUSION: Our results indicate that the insulin assay conducted on the Siemens Atellica platform could be used to diagnose factitious hypoglycemia by detecting the specific insulin analogs involved. The findings from our studies indicate the suitability of this method for clinical laboratory use in cases where factitious hypoglycemia is under consideration as a potential diagnosis. Clinicians should take these results into account when interpreting insulin measurements, particularly in instances where insulin analog overdose is suspected.