Hemolysis Affects C-Peptide Immunoassay

Tutorial review for peptide assays: An ounce of pre-analytics is worth a pound of cure

The recent increase in peptidomimetic-based medications and the growing interest in peptide hormones has brought new attention to the quantification of peptides for diagnostic purposes. Indeed, the circulating concentrations of peptide hormones in the blood provide a snapshot of the state of the body and could eventually lead to detecting a particular health condition. Although extremely useful, the quantification of such molecules, preferably by liquid chromatography coupled to mass spectrometry, might be quite tricky. First, peptides are subjected to hydrolysis, oxidation, and other post-translational modifications, and, most importantly, they are substrates of specific and nonspecific proteases in biological matrixes. All these events might continue after sampling, changing the peptide hormone concentrations. Second, because they include positively and negatively charged groups and hydrophilic and hydrophobic residues, they interact with their environment; these interactions might lead to a local change in the measured concentrations. A phenomenon such as nonspecific adsorption to lab glassware or materials has often a tremendous effect on the concentration and needs to be controlled with particular care. Finally, the circulating levels of peptides might be low (pico- or femtomolar range), increasing the impact of the aforementioned effects and inducing the need for highly sensitive instruments and well-optimized methods. Thus, despite the extreme diversity of these peptides and their matrixes, there is a common challenge for all the assays: the need to keep concentrations unchanged from sampling to analysis. While significant efforts are often placed on optimizing the analysis, few studies consider in depth the impact of pre-analytical steps on the results. By working through practical examples, this solution-oriented tutorial review addresses typical pre-analytical challenges encountered during the development of a peptide assay from the standpoint of a clinical laboratory. We provide tips and tricks to avoid pitfalls as well as strategies to guide all new developments. Our ultimate goal is to increase pre-analytical awareness to ensure that newly developed peptide assays produce robust and accurate results.

Difference in Insulin Resistance Assessment between European Union and Non-European Union Obesity Treatment Centers (ESPE Obesity Working Group Insulin Resistance Project)

INTRODUCTION

The obesity epidemic has become one of the most important public health issues of modern times. Impaired insulin sensitivity seems to be the cornerstone of multiple obesity related comorbidities. However, there is no accepted definition of impaired insulin sensitivity.

OBJECTIVE

We hypothesize that assessment of insulin resistance differs between centers.

METHODS

The ESPE Obesity Working Group (ESPE ObWG) Scientific Committee developed a questionnaire with a focus on the routine practices of assessment of hyperinsulinemia and insulin resistance, which was distributed through Google Docs platform to the clinicians and researchers from the current ESPE ObWG database (n = 73). Sixty-one complete responses (84% response rate) from clinicians and researchers were analyzed: 32 from European Union (EU) centers (representatives of 14 countries) and 29 from Non-EU centers (representatives from 10 countries). Standard statistics were used for the data analysis.

RESULTS

The majority of respondents considered insulin resistance (IR) as a clinical tool (85.2%) rather than a research instrument. For the purpose of IR assessment EU specialists prefer analysis of the oral glucose tolerance test (OGTT) results, whereas non-EU ones mainly use Homeostatic Model Assessment of Insulin Resistance (HOMA-IR; p = 0.032). There was no exact cutoff for the HOMA-IR in either EU or non-EU centers. A variety of OGTT time points and substances measured per local protocol were reported. Clinicians normally analyzed blood glucose (88.52% of centers) and insulin (67.21%, mainly in EU centers, p = 0.0051). Furthermore, most participants (70.5%) considered OGTT insulin levels as a more sensitive parameter of IR than glucose. Meanwhile, approximately two-thirds (63.9%) of the centers did not use any cutoffs for the insulin response to the glucose load.

CONCLUSIONS

Since there is no standard for the IR evaluation and uniform accepted indication of performing, an OGTT the assessment of insulin sensitivity varies between EU and non-EU centers. A widely accepted standardized protocol is needed to allow comparison between centers.

Influence of hemolysis on serum procalcitonin measured by electrochemiluminescence in an emergency room

BACKGROUND

To investigate the effect of hemolysis on serum procalcitonin (PCT) detected by electrochemiluminescence (ECL) and to explore the possibility of establishment of a correction equation.

METHODS

Fifty-one blood samples from 17 patients were collected. Hemolytic samples, of which the final concentrations of hemoglobin (Hb) were 5, 10, 15 and 20 g L^-1, were prepared by adding lysed homologous RBCs to serum, and then the PCT levels were detected and compared.

RESULTS

with the increasing degree of sample hemolysis, PCT bias elevated from -13.12% to -38.86% as the hemolysis degree increased from 5 g L^-1 to 20 g L^-1, respectively. There was a linear correlation of PCT levels between the original and hemolytic samples with the same hemolytic degree (r > 0.97). Using the correction equation log₁₀PCT_corr = 0.962(log₁₀PCT_hemo) +0.251(log₁₀Hb) - 0.126, the corrected PCT values from the hemolytic samples showed acceptable consistency with the original values (p > 0.05).

CONCLUSIONS

Hemolysis has a negative interference on PCT values assayed by ECL. The serum PCT level is correlated negatively with the Hb level in the blood sample. The established correction equation could reduce inappropriate antibiotics application and improve the experience of patients in the emergency department.

Role of umbilical cord C-peptide levels in early prediction of hypoglycemia in infants of diabetic mothers

BACKGROUND

Until now, diabetes during pregnancy has been associated with a high risk of maternal, fetal, and neonatal morbidities and mortalities. The main aim of this study was to evaluate the risk factors of hypoglycemia in infants of diabetic mothers (IDMs) and to study the relationship between umbilical cord (UC) C peptide levels and the risk of developing hypoglycemia.

MATERIAL AND METHODS

UC blood C-peptide and serial serum blood glucose measurements were done for all included singleton newborns born to diabetic mothers during the study period. Maternal and neonatal data such as gestational age, maternal age, maternal weight, types of diabetics and its control, maternal glycated hemoglobin (HbA1C), birth weight, Apgar score, and neonatal complete blood picture were collected.

RESULTS

In total, 83 IDMs met the inclusion criteria. Fifty-four (65.06%) developed hypoglycemia and 29 (34.94%) remained normoglycemic. However, there were no significant differences between hypoglycemic and normoglycemic IDMs in terms of types of maternal diabetics (P value = 0.41), its duration (P value = 0.43). The hypoglycemia peak occurred within the first 3 h of life, with 33.11 ± 8.84 mg/dl for the hypoglycemia group and 54.10 ± 6.66 mg/dl for the normoglycemic group (P value < 0.0001). Most of the babies had no hypoglycemic manifestation (96.30%). Neonates with hypoglycemia their mothers had poor diabetes control in the last trimester (HbA1C 7.09 ± 0.96%) compared to normoglycemic babies (HbA1C 6.11 ± 0.38%), (P-value < 0.0001). The mean (SD) of UC C-peptide level in hypoglycemic neonates increased to 1.73 ± 1.07 ng/ml compared to normoglycemic ones with 1.08 ± 0.81 ng/ml (P value = 0.005).

CONCLUSION

Poor diabetes control, especially in the last trimester, is associated with neonatal hypoglycemia. Increased UC C-peptide levels could be used as an early indicator for the risk of developing neonatal hypoglycemia and a predictor for babies need neonatal admission.