Impact of insulin adsorption in various containers during hyperkalaemia treatment

Potassium homeostasis - Physiology and pharmacology in a clinical context

Membrane voltage controls the function of excitable cells and is mainly a consequence of the ratio between the extra- and intracellular potassium concentration. Potassium homeostasis is safeguarded by balancing the extra-/intracellular distribution and systemic elimination of potassium to the dietary potassium intake. These processes adjust the plasma potassium concentration between 3.5 and 4.5 mmol/L. Several genetic and acquired diseases but also pharmacological interventions cause dyskalemias that are associated with increased morbidity and mortality. The thresholds at which serum K+ not only associates but also causes increased mortality are hotly debated. We discuss physiologic, pathophysiologic, and pharmacologic aspects of potassium regulation and provide informative case vignettes. Our aim is to help clinicians, epidemiologists, and pharmacologists to understand the complexity of the potassium homeostasis in health and disease and to initiate appropriate treatment strategies in dyskalemic patients.

Multiplexed quantification of insulin and C-peptide by LC-MS/MS without the use of antibodies

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Simultaneous quantification of insulin and C-peptide without antibodies.

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Proteolysis with Glu-C permits sensitive and precise measurements.

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Calibration with certified reference material provides traceability.

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Relatively large bias when compared with a commercially available immunoassay.

Introduction

The measurement of insulin and C-peptide provides a valuable tool for the clinical evaluation of hypoglycemia. In research, these biomarkers are used together to better understand hyperinsulinemia, hepatic insulin clearance, and beta cell function. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is an attractive approach for the analysis of insulin and C-peptide because the platform is specific, can avoid certain limitations of immunoassays, and can be multiplexed. Previously described LC-MS/MS methods for the simultaneous quantification of insulin and C-peptide measure the intact analytes and most have relied on immunoaffinity enrichment. These approaches can be limited in terms of sensitivity and interference from auto-antibodies, respectively. We have developed a novel method that does not require antibodies and uses proteolytic digestion to yield readily ionizable proteotypic peptides that enables the sensitive, specific, and simultaneous quantitation of insulin and C-peptide.

Methods

Serum samples were precipitated with acetonitrile. Analytes were enriched using solid phase extraction and then digested with endoproteinase Glu-C. Surrogate peptides for insulin and C-peptide were analyzed using targeted LC-MS/MS.

Results

Inter-day imprecision was below 20 %CV and linearity was observed down to the lower limit of quantitation for both analytes (insulin = 0.09 ng/mL, C-peptide = 0.06 ng/mL). Comparison to a commercially available insulin immunoassay (Beckman Coulter UniCel DxI 600 Access) revealed a 30% bias between methods.

Conclusion

A novel LC-MS/MS method for the simultaneous analysis of insulin and C-peptide using Glu-C digestion was developed and evaluated. A detailed standard operating procedure is provided to help facilitate implementation in other laboratories.

Observational study of the relative efficacy of insulin-glucose treatment for hyperkalaemia in patients with liver cirrhosis

OBJECTIVES

To determine if liver cirrhosis is associated with reduced efficacy of insulin-glucose treatment in moderate to severe hyperkalaemia.

DESIGN

Retrospective, cohort study.

SETTING

Two secondary and one tertiary care hospital at a large metropolitan healthcare network in Melbourne, Australia.

PARTICIPANTS

This study included 463 adults with a mean age of 68.7±15.8 years, comprising 79 patients with cirrhosis and 384 without cirrhosis as controls, who received standard insulin-glucose treatment for a serum potassium ≥6.0 mmol/L from October 2016 to March 2020. Patients were excluded if they received an insulin infusion, or if there was inadequate follow-up data for at least 6 hours after IDT due to death, lost to follow-up or inadequate biochemistry monitoring. The mean Model for End-stage Liver Disease score in patients with cirrhosis was 22.2±7.5, and the distribution of the Child-Pugh score for cirrhosis was: class A (24%), class B (46%), class C (30%).

OUTCOME MEASURES

The primary outcome was the degree of potassium lowering and the secondary outcome was the proportion of patients who achieved normokalaemia, within 6 hours of treatment.

RESULTS

The mean pretreatment potassium for the cohort was 6.57±0.52 mmol/L. After insulin-glucose treatment, mean potassium lowering was 0.84±0.58 mmol/L in patients with cirrhosis compared with 1.33±0.75 mmol/L for controls (p<0.001). The proportion of patients achieving normokalaemia was 33% for patients with cirrhosis, compared with 53% for controls (p=0.001). By multivariable regression, on average, liver cirrhosis was associated with a reduced potassium lowering effect of 0.42 mmol/L (95% CI 0.22 to 0.63 mmol/L, p<0.001) from insulin-glucose treatment, after adjusting for age, serum creatinine, cancer, pretreatment potassium level, β-blocker use and cotreatments (sodium polystyrene sulfonate, salbutamol, sodium bicarbonate).

CONCLUSIONS

Our observational data suggest reduced efficacy of insulin-glucose treatment for hyperkalaemia in patients with cirrhosis.