Comparision Study of Procalcitonin Assay between Roche Cobas e411 and BRAHMS Kryptor compact PCT Instrument at Queen Sirikit National Institute
Procalcitonin (PCT) is now used as a new biomarker for clinical diagnosis of bacterial infection and early diagnosis of sepsis that is more specific and earlier than using white blood cell count and blood cultures. PCT is also used as a parameter to guide the antibiotic therapy especially in respiratory tract infection. This study aims to compare PCT from Roche Cobas e411 (electrochemiluminescence immunoassay (ECLIA)) with that from BRAHMS Kryptor compact PCT (amplified cryptate emission (TRACE)). Ninety-one routine samples covering low, normal and high levels from IPD patients conducted during August 1 to October 31, 2017. The samples were divided into 2 groups of concentrations, 0.2-20.0 ng/mL and 20.0-270.0 ng/mL. The EP Evaluator program was used to evaluate all data. The results showed that the precision (total % CV) of PCT from the two instruments were 1.92% and 4.45% respectively. The correlation coefficient (r) of the first group (0.2-20.0 ng/mL) and the second group (20.1-270.0 ng/mL) were 0.992, and 0.990 with the slope of 1.065 and 0.999 (Deming regression) respectively. Even though correlation coefficient of both groups were nearly 1.0 which showed the concordance between Cobas e411 and BRAHMS Kryptor compact but the total error (20.3%) from Bland Altman Plot showed the difference at each point with higher values of BRAHMS Kryptor compact. The first group (61 of 61 samples) was within range criteria (-0.99 to 0.83) (100%) whereas the second group (28 of 30 samples) was with 2 out of criteria (-0.63 to 1.54) (93.3%). We can conclude that PCT from the two instruments showed a good correlation, precision and concordance ranged from 0.2-20.0 ng/mL, but for the concentration from 20.0-270.0 ng/mL higher values were obtained from BRAHMS Kryptor
compact and Cobas e411 also gave a better precision. In addition to statistical study, other factors have to be considered such as large measuring range (dilution factor) that is so important for the small volume of specimen especially for newborn, stability of opened reagents, frequency of calibration, on board dilution, analytical performances (multi-assay or single assay instrument), patient character and price. All these factors are important for laboratory in choosing suitable instruments that meet the acceptable criteria for each institution.
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