Evaluation of volumetric blood collection devices for the measurement of phenylalanine and tyrosine to monitor patients with phenylketonuria.

BACKGROUND

Measurement of dried blood spot (DBS) phenylalanine (Phe) is central to the monitoring of patients with phenylketonuria. However, the volume and hematocrit (Hct) of the blood applied to conventional DBS cards significantly affects analytical results. Volumetric blood collection devices are reported to be more accurate, precise and less prone to Hct effects.

METHODS

Accuracy, imprecision, effect of blood volume and Hct were evaluated for measurement of Phe and tyrosine using three volumetric devices and compared with the conventional PerkinElmer-226 filter-paper collection devices. i.e. conventional DBS cards. Applicability for use in a clinical laboratory was assessed qualitatively.

RESULTS

Blood volume did not impact on the performance of the volumetric devices; however, significant biases were observed with the conventional DBS card. A higher Hct introduced unacceptable bias for Neoteryx-Mitra and conventional DBS card. All devices had a mean relative standard deviation (RSD) ≤ 4.1 %, except for the Neoteryx-Mitra (≤ 6.2 %). Relative to liquid blood, the mean biases of Phe for the various devices were -5.1 (HemaXis-DB10), -7.8 (Capitainer-qDBS), -12.0 (Neoteryx-Mitra) and -32.6 % (conventional DBS card).

CONCLUSIONS

Introducing volumetric collection devices will overcome the significant pre-analytical issues associated with conventional DBS collection and improve the biochemical monitoring of patients with PKU.