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Abstract |
Assay of Free Insulin in Serum of IDDM Patients: Performance of a PEG Precipitation Technique in Conjunction with an Ultrasensitive Human Insulin RIA with Regular Human Insulin and Lipidic Carriers |
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Determination of insulin concentrations may become a laboratory challenge especially in the case of clinical trials in patients with insulin therapy, when the insulin levels measured with a radioimmunoassay may comprise of free and antibody-bound insulin. To support clinical studies in a type 1 diabetic population treated with small amounts of insulin, a refïned insulin assay methodology was developed. We used PEG precipitation in conjunction with an ultrasensitive human insulin RIA assay to circumvent the interference of endogenous anti-insulin antibodies present in the blood of diabetic patients on long term insulin therapy. Furthermore, we evaluated the ability of this protocol to discern low amounts of insulin in the presence of potentially interfering lipidic carriers of the drug. The reported assay protocol is suitable for measuring free insulin with an accuracy of 70 - 101% from type 1 patient and healthy volunteer serum samples with a precision of 2 - 11% within run and 11 - 20% between runs. Free insulin in serum can be determined with acceptable accuracy even when lipids, in the form of a vesicular suspension, are added to the investigated sample. |
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