Undisclosed interference in 25-OH-Vitamin D immunoassay on Liaison XL analyzer when using heparin plasma tubes

This study investigates the impact of sample type on the measurement of 25-OH-vitamin D using the Liaison XL (Diasorin) and Cobas e801 (Roche). This investigation was motivated by the need to optimize sample volume usage, which led us to adopt the use of heparin plasma, an alternative proposed by Diasorin in their specification. Discordant and unexplainable results were observed, prompting us to evaluate the effect of sample type on the accuracy of the 25-OH-vitamin D measurements. We collected 34 different paired samples from a randomly selected patients who had two types of tubes taken simultaneously: serum-gel and lithium-heparin plasma tubes. The 25-OH-vitamin D levels were measured using Cobas e801 and Liaison. Statistical analysis was performed using the Mann-Whitney test to calculate the p-value. Biases were also calculated. When comparing the heparin matrix with the serum matrix on the Liaison XL analyzer, a higher proportion (p < .0001; 79% versus 64%) of patients were classified in the 'normal group', while fewer were classified in the 'insufficiency' or 'deficiency group'. The heparin tubes on the Liaison XL analyzer showed a mean bias of 57.5%) (p-value < .001; 95%CI: 37.6-77.4) compared to the serum tubes. On the other hand, the heparin tubes on the Cobas e801 analyzer showed a mean bias of -0.2% (95%CI: -4.8 to 4.5) compared to the serum tubes. It is imperative for laboratory professionals to be aware of this interference for an accurate measurement of 25-OH-vitamin D levels on the Liaison XL. Further research is needed to understand the mechanism of this interference.