Insulin measurement

Figure Bl.15.14. Comparison of 95.1 GHz (A) and 9.71 GHz (B) EPR spectra for a frozen solution of a nitroxide spin label attached to insulin measured at 170 K.

Several tests use glucagon to diagnose endocrine disorders. In patients with type 1 diabetes mellitus, a classic research test of pancreatic beta-cell secretory reserve uses 1 mg of glucagon administered as an intravenous bolus. Because insulin-treated patients develop circulating anti-insulin antibodies that interfere with radioimmunoassays of insulin, measurements of C-peptide are used to indicate beta-cell secretion. 

Many authors used mice instead of rats (Gross et al. 1994, Bailey et al. 1997, Ahren et al. 2000). However, parallel insulin measurements are much more limited in mice than in rats. Also oGTT in insulin resistant animal disease models in mice (e.g. genetic ob/ob, db/db, Ay) are described to assess peripheral insulin resistance (Xiao et al. 2001, Arakawa et al. 2001, Nagakura et al. 2003, Thorkildsen et al. 2003, Minoura et al. 2004). Other routes for glucose administration (e.g. intraperitoneal) are also reported (Xie et al. 2004). 

Blood samples were taken at 30 min for determination of baseline insulin levels and at 180, 210 and 240 min for determination of insulin levels under hyperinsulinemia. At 120 and at 240 min, additional blood samples for determination of fee fatty acids are taken. Animals were killed by pentobarbital overdose. Metabolic blood parameters are determined using standard methods (Bergmeyer 1974) insulin measurements are performed using commercially available radioimmunoassay or ELISA kits. 

Measurement of C-peptide has a number of advantages over insulin measurement. Because hepatic metabolism is negligible, C-peptide concentrations are better indicators of P-ceU ffinction than is peripheral insulin concentration. Furthermore, C-peptide assays do not measure exogenous insulin and do not cross-react with insulin antibodies, which interfere with the insulin immunoassay. 

Principle. In a typical RIA procedure for measuring insulin, T-labeled insulin competes with insulin in a patient sample for binding to an insuhn-specific antibody immobilized on the walls of a polypropylene tube. The supernatant is decanted, and the bound determined in a gamma counter. The amount of insulin in the sample is established by comparison with a calibration curve obtained by plotting on logit-log graph paper the percent of total radioactivity bound (B/T%) against the concentration of the calibrators. Various commercial kits for insulin measurement are now available. 

Plasma insulin. Insulin measurements can lead to the diagnosis or exclusion of insulinoma. They play no part in the diagnosis of diabetes mellitus. 

Insulin/gliicose ratio. In order to make better diagnostic use of insulin measurements, the ratio of insulin and glucose concentrations, measured on the same sample, is reported. 

Sapin, R., J-C. Ongagna, F. Gasser, and D. Grucker. 1998. Insulin measurements in hemolyzed serum Influence of insulinase inhibitors. Clinica ChimicaActa 274 111-117. 

What comes out of the interrogation interface is stored in a computer. For the insulin measurement being used for illustration, the TOF values for the calibration ions are identified by the interrogation module and stored in a separate computer file which sorts by TOF value and records the frequency distributions of TOF values. All other TOF values are truncated to 1 ns resolution and stored in a file that will be used to generate the mass spectrum over the recorded mass range. The sequence of events is depicted in Figure 7. 

The concentration of insulin in a production vat is determined by the method of isotope dilution. A 1.00-mg sample of insulin labeled with with an activity of 549 cpm, is added to a 10.0-mL sample taken from the production vat. After homogenizing the sample, a portion of the insulin is separated and purified, yielding 18.3 mg of pure insulin. The activity for the isolated insulin is measured at 148 cpm. How many milligrams of insulin are in the original sample ... 

When the insulin dose is incorrectiy measured and is greater tiian that prescribed... 

Insulin is available in concentrations of U100 and U500. The nurse must read the label of die insulin bottle carefully for the name, source of insulin (eg, human, beef, pork, beef and pork, purified beef), and die number of units per milliliter (U/ mL). The dose of insulin is measured in units (U). U100 insulin has 100 units in each milliliter U500 has 500 units in each milliliter. Most people with diabetes use the U100 concentration. Fhtients who are resistant to insulin and require large insulin doses require the U500 concentration. 

---