Evaluation of an Alternate Diluent for Tests to Ensure Timely Patient Management

Abstract Introduction/Objective Recently, backorder of Multi-diluent (MD) for various assays on ADVIA Centaur analyzer (Siemens Healthineers) led to delay in reporting numeric values to the clients when results above the analytical measurement range (AMR) had to be reported as “> value”. The samples were stored frozen (-20 degrees Celsius or - 80 degrees Celsius) for over 2 weeks until the diluent became available, then thawed and re-analyzed upon appropriate dilution. Delay in reporting results beyond AMR may impact patient management; therefore, this study evaluated saline as an alternative diluent for serum folate, carbohydrate antigen 19-9 (CA 19-9), and carbohydrate antigen 27-29 (CA 27.29). Methods/Case Report For each test, samples from 5 patients were tested in duplicate, and average of the results was considered the target value (results within undiluted AMR). Subsequently, the samples were diluted 20-fold with either MD or saline, tested in duplicate and average of the results was compared to the target value. The diluent was considered acceptable for use if the difference or % difference between diluted vs target value was less than the Total Allowable Error (TEA). Results (if a Case Study enter NA) For serum folate and CA 19-9, the bias between diluted and target value for each diluent (saline and Multi-diluent) was < TEA, and the average bias was also < TEA. For CA 19-9, the average difference from target for saline was smaller than that for Multi-diluent, suggesting it performs better (p-value of 0.0035). However, saline was not an acceptable diluent for CA 27.29 as the bias exceeded TEA. Conclusion Saline was an acceptable alternative diluent for serum folate and CA 19-9 but not for CA27.29.