Reference range of the IGF-1 concentration in feline plasma using an immunochemiluminescence assay
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In 20-25% of all cats with diabetes mellitus the diabetes is secondary to a different disease, for example hypersomatotropism. This disease is caused by an anterior pituitary tumour. For the optimal treatment, it is important to find the underlying cause of the diabetes. The plasma insulin-like growth factor-1 (IGF-1) concentration is a reliable indicator for hypersomatotropism. The current method, i.e. radioimmunoassay, uses radioactive material, only takes place when enough samples are received and is costly. With the new method, the immunochemiluminescence assay, the waiting period will be significantly shorter, radioactive material will not be used and the costs would be lower. The goal of this research is to find a reference range for the IGF-1 concentration in feline plasma samples measured with an immunochemiluminescence assay. 92 plasma samples were selected from leftover feline plasma samples sent to the UVDL between January and October 2014 for measurements not related to IGF-1. 42 samples were sent in by veterinarians of the university clinic and 50 samples were sent in by external first-opinion veterinarians in the Netherlands. The selection criteria were >6 years of age, with no kidney or liver disease, hypersomatotropism or diabetes in their medical history. All the samples were measured using the Immulite 2000® (Siemens) preceded by extraction with ethanol-formic acid to separate the IGF-1 molecules from its ternary complex with IGFBP and ALS. Within the 92 samples, 7 had a plasma IGF-1 concentration of >900ng/ml. Of these samples, 5 were excluded from the study because the patients were previously diagnosed with kidney disease. Using a box-and-whiskers plot with a 95% right-sided reference interval, the reference range was calculated to be <795ng/ml. Using this method and its reference range, it will be possible to measure the plasma IGF-1 in patients’ blood samples on a weekly basis. Future research can be performed to optimise the sample group by using only healthy individuals and reducing the amount of variables between samples.