Variable characteristics with insulin assays

Clinical Case of Surreptitious Hypoglycemia Due to Deliberate Insulin Analog Administration

Hypoglycemic syndrome is a life-threatening condition that can lead to hypoglycemic coma and death. Surreptitious hypoglycemic syndrome is the deliberate use of insulin preparations or oral hypoglycemic drugs aimed to reduce blood glucose level. If human insulin is injected, high level of immunoreactive insulin (IRI) and low level of C-peptide at the moment of hypoglycemia are always detected. However, the fact of deliberate administration of insulin analogs is difficult to prove. In these cases if insulin kit test with low cross-reactivity with insulin analogs is used, the low levels of IRI and C-peptide will be suspected. Some experts suggest the presence of cross reactivity with analogs of insulin in a number of commercial kits, which makes it possible to detect cases of surreptitious hypoglycemia. We present a clinical case of a patient with surreptitious hypoglycemia due to the administration of insulin analogs and discuss the problems of its laboratory diagnosis.

Clinical Utility and Cross-Reactivity of Insulin and C-Peptide Assays by the Lumipulse G1200 System

BACKGROUND

Measurement of insulin and C-peptide concentrations is important for deciding whether insulin treatment is required in diabetic patients. We aimed to investigate the analytical performance of insulin and C-peptide assays using the Lumipulse G1200 system (Fujirebio Inc., Tokyo, Japan).

METHODS

We examined the precision, linearity, and cross-reactivity of insulin and C-peptide using five insulin analogues and purified proinsulin. A method comparison was conducted between the Lumipulse G1200 and Roche E170 (Roche Diagnostics, Mannheim, Germany) systems in 200 diabetic patients on insulin treatment. Reference intervals for insulin and C-peptide concentrations were determined in 279 healthy individuals.

RESULTS

For insulin and C-peptide assays, within-laboratory precision (% CV) was 3.78-4.14 and 2.89-3.35%, respectively. The linearity of the insulin assay in the range of 0-2,778 pmol/L was R²=0.9997, and that of the C-peptide assay in the range of 0-10 nmol/L was R²=0.9996. The correlation coefficient (r) between the Roche E170 and Lumipulse G1200 results was 0.943 (P<0.001) for insulin and 0.996 (P<0.001) for C-peptide. The mean differences in insulin and C-peptide between Lumipulse G1200 and the Roche E170 were 19.4 pmol/L and 0.2 nmol/L, respectively. None of the insulin analogues or proinsulin showed significant cross-reactivity with the Lumipulse G1200. Reference intervals of insulin and C-peptide were 7.64-70.14 pmol/L and 0.17-0.85 nmol/L, respectively.

CONCLUSIONS

Insulin and C-peptide tests on the Lumipulse G1200 show adequate analytical performance and are expected to be acceptable for use in clinical areas.

Gut microbiota-based translational biomarkers to prevent metabolic syndrome via nutritional modulation

In the face of the global epidemic of metabolic syndrome (MetS) and its strong association with the increasing rate of cardiovascular morbidity and mortality, it is critical to detect MetS at an early stage in the clinical setting to implement preventive intervention long before the complications arise. Lipopolysaccharide, the cell wall component of Gram-negative bacteria produced from diet-disrupted gut microbiota, has been shown to induce metabolic endotoxemia, chronic low-grade inflammation, and ultimately insulin resistance. Therefore, ameliorating the inflammation and insulin resistance underlying MetS by gut microbiota-targeted, dietary intervention has gained increasing attention. In this review, we propose using dynamic monitoring of a set of translational biomarkers related with the etiological role of gut microbiota, including lipopolysaccharide binding protein (LBP), C-reactive protein (CRP), fasting insulin, and homeostasis model assessment of insulin resistance (HOMA-IR), for early detection and prevention of MetS via nutritional modulation. LBP initiates the recognition and monomerization of lipopolysaccharide and amplifies host immune responses, linking the gut-derived antigen load and inflammation indicated by the plasma levels of CRP. Fasting plasma insulin and HOMA-IR are measured to evaluate insulin sensitivity that is damaged by pro-inflammatory cytokines. The dynamic monitoring of these biomarkers in high-risk populations may provide translational methods for the quantitative and dynamic evaluation of dysbiosis-induced insulin resistance and the effectiveness of dietary treatment for MetS.