Effects of insulin therapy upon plasma lipid fatty acids and platelet aggregation in NIDDM with secondary failure to oral antidiabetic agents

Comparison of four matrixes for diluting insulin in routine clinical measurements

Objective

In our laboratory, 2.36% (6626/280765) samples obtained for insulin evaluation have serum insulin concentrations higher than 300 mU/L, resulting in curves outside the linear range in the insulin release test (IRT). Accordingly, using appropriate dilution protocols to determine insulin concentration accurately is important. Here, we compared the effectiveness and economy of four different solutions for diluting high‐insulin serum in routine clinical measurements.

Method

Residual serum samples with high‐insulin concentrations ranging from 200 to 300 mU/L were collected in Peking Union Medical College Hospital from August to November 2017. Four different matrixes including a Siemens original diluent, pure water, 0.9% NaCl, and low‐insulin serum (labeled as A to D, respectively) were used to dilute the serum in the ratios of 1:2, 1:5, and 1:10.

Results

We found that the linear correlation coefficients of A to D were higher than 0.9. The recovery rates of A to D were 86.4%–104.0%, 73.2%–99.3%, 76.4%–101.3%, and 84.2%–99.7%, respectively. We conclude that the use of 0.9% NaCl, pure water, or low‐insulin serum to dilute high‐serum insulin (>300 mU/L) is feasible and cost‐effective.

Conclusion

We recommend a dilution factor of 1:5 on a Siemens ADVIA Centaur XP^® instrument. The clinically reported range was 0.5‐1500 mU/L. For specific samples (>1500 mU/L), we recommended using low‐insulin serum samples for dilution.

Insulin monotherapy versus combinations of insulin with oral hypoglycaemic agents in patients with type 2 diabetes mellitus

BACKGROUND

It is unclear whether patients with type 2 diabetes who have poor glycaemic control despite maximal oral hypoglycaemic agents (OHAs) should be commenced on insulin as monotherapy, or insulin combined with oral hypoglycaemic agents (insulin-OHA combination therapy).

OBJECTIVES

To assess the effects of insulin monotherapy versus insulin-OHA combinations therapy.

SEARCH STRATEGY

Eligible studies were identified by searching MEDLINE, EMBASE, and The Cochrane Library. Date of last search: May 2004.

SELECTION CRITERIA

Randomised controlled trials (RCTs) with 2 months minimum follow-up duration comparing insulin monotherapy (all schemes) with insulin-OHA combination therapy.

DATA COLLECTION AND ANALYSIS

Data extraction and assessment of study quality were undertaken by three reviewers in pairs.

MAIN RESULTS

Twenty RCTs (mean trial duration 10 months) including 1,811 participants, with mean age 59.8 years and mean known duration of diabetes 9.6 years. Overall, study methodological quality was low. Twenty-eight comparisons in 20 RCTs were ordered according to clinical considerations. No studies assessed diabetes-related morbidity, mortality or total mortality. From 13 studies (21 comparisons), sufficient data were extracted to calculate pooled effects on glycaemic control. Insulin-OHA combination therapy had statistically significant benefits on glycaemic control over insulin monotherapy only when the latter was applied as a once-daily injection of NPH insulin. Conversely, twice-daily insulin monotherapy (NPH or mixed insulin) provided superior glycaemic control to insulin-OHA combination therapy regimens where insulin was administered as a single morning injection. In more conventional comparisons, regimens utilising OHAs with bedtime NPH insulin provided comparable glycaemic control to insulin monotherapy (administered as twice daily, or multiple daily injections). Overall, insulin-OHA combination therapy was associated with a 43% relative reduction in total daily insulin requirement compared to insulin monotherapy. Of the 14 studies (22 comparisons) reporting hypoglycaemia, 13 demonstrated no significant difference in the frequency of symptomatic or biochemical hypoglycaemia between insulin and combination therapy regimens. No significant differences in quality of life related issues were detected. Combination therapy with bedtime NPH insulin resulted in statistically significantly less weight gain compared to insulin monotherapy, provided metformin was used +/-sulphonylurea. In all other comparisons no significant differences with respect to weight gain were detected.

REVIEWERS' CONCLUSIONS

Bedtime NPH insulin combined with oral hypoglycaemic agents provides comparable glycaemic control to insulin monotherapy and is associated with less weight gain if metformin is used.