This assay will allow measurement of free insulin by removal of anti- insulin antibodies with PEG (polyethylene glycol). This assay is intended for patients where it is suspected that the insulin assay is interfered with by auto-antibodies to insulin. This most commonly occurs with patients treated with non-human insulins (e.g., cow or pig) and is very rare for patients treated with the modern recombinant human insulins. An analysis of data in the Chemistry laboratory from 2006- 2009 indicated that the rate of antibody interference with the insulin assay is less than 1 in 3,000 patients. The laboratory will report results both with PEG precipitation (free insulin) and without PEG precipitation (total insulin). A glucose will be automatically done on each specimen at no additional charge. This insulin assay does NOT measure the insulin analogs lispro (Humalog), aspart (NovoLog), and glargine (Lantus). Please contact the laboratory if an assay with cross-reactivity to these insulin analogs is required.

The assay is unaffected by icterus (bilirubin is less than 90 mg/dL), lipemia (Intralipid is less than 1800 mg/dL) and biotin is less than 60 ng/mL (criterion: recovery within plus or minus 10% of initial value). Hemolysis interferes. In patients receiving therapy with high biotin doses (i.e. is greater than 5 mg/day) no sample should be taken until at least 8 hours after the last biotin administration. Samples from patients treated with bovine or porcine insulin sometimes contain anti-insulin antibodies which can affect the test results.(1-2) As with all tests containing monoclonal mouse antibodies, erroneous findings may be obtained from samples taken from patients who have been treated with monoclonal mouse antibodies or have received them for diagnostic purposes. Elecsys Insulin contains additives which minimize these effects. In rare cases, interference due to extremely high titers of antibodies to streptavidin can occur. For diagnostic purposes, Insulin findings should always be assessed in conjunction with the patient's medical history, clinical examination and other findings. (1) Fiedler, H. Basiswissen Labordiagnostik: Diabetes mellitus und metabolisches Syndrom. Roche Diagnostics Brochure 1999;14,67 Cat No. 1951769. (2) Tietz NW. Clinical Guide To Laboratory Tests. 3rd ed. Philadelphia, Pa: WB Saunders Co, 1995:366-367.