Endocrine Abstracts

Introduction: Responsible use of healthcare resources dictates that judicious test ordering be encouraged. Although the appearance of anti-GAD antibodies is known to precede and predict the development of autoimmune diabetes, its use as a screen for risk of developing diabetes is not warranted. Results are useful in determining treatment, however, when it is difficult to distinguish type 1 from type 2 diabetes or when the probability of progression from type 2 to type 1 is high. Method: Anti-GAD measurement was initially made available only to Endocrinologists in the Edmonton Region. The correlation between C-peptide levels and anti-GAD positivity was examined to determine if, as suggested in the literature, there is a C-peptide level above which the probability of the presence of antibody was low. Results: An overall sensitivity of 93% and specificity of 70% was observed using a C-peptide cut-off of 0.80 nmol/l. The anti-GAD positive samples with a C-peptide >0.80 nmol/l were from pediatric patients. The laboratory then accepted orders from any physician but implemented criteria for processing requests which included identification of the patient as a diabetic based on HbA1c values or elevated glucose levels and C-peptide levels <0.80 nmol/l (normal 0.30–1.32 nmol/l). The Laboratory Information System was programmed to pull the required data and flag those specimens that did not meet the criteria. A positivity rate of 47% was observed when testing was confined to Endocrinologists. With requests accepted from all physicians but restricted using the given criteria the positivity rate was 73%. An audit of pediatric samples continues. Conclusion: Programming the LIS to identify appropriate requests for anti-GAD has been successful in ensuring the test is not used for screening but is available when the result may alter treatment.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.