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Abstract Background Serum ß-hCG is levels are a useful marker for diagnosis of Gestational Trophoblastic Disease as well as germ cell tumours of the ovary and testicle. However, values ranging from 50,000 - 1,00,000 mIU/ml are commonly seen in malignancies which are beyond the linearity of the most methods used in routine practice. This poses a great challenge to laboratory professionals while reporting for this test as serial monitoring of ß-hCG values is essential for ascertaining the effectiveness of treatment and progression of disease in oncology patients. The aim of this study was to develop a protocol for reporting beyond linearity values of serum ß-hCG in our laboratory with comparison of the same on two analysers with different linearity. Methods One hundred and fifty serum samples for ß-hCG received from patients with trophoblastic as well as germ cell tumours over a period of three months from October 2023 to December 2023 were processed by Chemiluminescence Immunoassay (CLIA) method on Atellica IM (Siemens Healthineers) and Alinity-i (Abbott Healthcare) immunoassay analysers simultaneously. The linearity for Atellica IM is 0 -1000mIU/ml and same for Alinity-i is 0- 15,000 mIU/ml as reported by the manufacturer. The protocol followed for samples processed on Atellica IM was as follows with 50 samples in each group. For values of ß-hCG less than 500 mIU/ml, we repeat tested samples with 1:10 dilution in case any instrument flags were observed in the report. For values between 500-1000 mIU/ml, samples were repeat tested with 1:50 dilution. For values reported as 1000 mIU/ml, samples were repeat tested with 1:5000 dilutions. For Alinity-i, samples with values higher than 15,000 mIU/ml were processed with a dilution of 1:10. For all results with instrument flags, the dilution protocol was followed. Diluent provided by the manufacturer was used for all sample dilution processes. The values obtained on both analysers were compared statistically for correlation using linear regression analysis and coefficient of correlation (R) was calculated. Results The serum ß-hCG values observed ranged from 102 mIU/ml to 187,000 mIU/ml. Linear regression analysis for all groups showed good correlation. For serum ß-hCG values 500 mIU/ml; between 500-1000 mIU/ml and 1000 mIU/ml coefficient of correlation was observed as R=0.9987, 0.9936 and 0.9713 respectively. Conclusions Good correlation was observed between values of serum ß-hCG obtained by dilution protocol on Atellica IM and Alinity-i analysers. The protocol developed by our laboratory to report beyond linearity sample results on Atellica IM can be a very useful tool in oncology patients where high values of beta HCG are expected and serial monitoring of values is essential.
Chavan et al. (Tue,) studied this question.