Agreement between procalcitonin measurements using the new point-of-care testing ichroma™ reader and the automated Kryptor instrument

To evaluate if procalcitonin (PCT) measurements made using the new point-of-care testing (POCT) ichroma™ are interchangeable with those made using Kryptor. Serum samples (n = 117) were processed sequentially on Kryptor and ichroma™. Statistical analysis was performed using Passing-Bablok (PB) regression and the Bland-Altman (BA) test. Cohen's kappa statistic was used to calculate the concordance at the clinically relevant cutoffs. PB regression did not show a significant deviation from linearity; proportional and constant differences were observed between ichroma™ and Kryptor. The 95% confidence interval (CI) of the mean bias percentage was very large, exceeding the maximum allowable total error (TE) (approximately 20%) and the clinical reference change value (about 60%). However, the concordance between methods at the clinically relevant cutoffs was strong, with the exception of the 0.25 ng/mL cutoff, which was moderate. Our data suggest that ichroma™ is not interchangeable with Kryptor, so cannot be mixed; one must choose one instrument only and be consistent. However, while the strong concordance at the clinically relevant cutoffs allows us to consider ichroma™ a suitable option to Kryptor to support clinicians' decision-making, nevertheless the moderate agreement at the 0.25 ng/mL cutoff recommends caution in interpreting the data around this cutoff.