Conference Paper

UTILIZATION OF A NORMAL “ZERO” STANDARD LEADS TO BETTER REPRODUCIBILITY AND DISCRIMINATION AT THE LOW END VALUES IN PKU SCREENING

Authors:
  • R&D Diagnostics Ltd
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Abstract

ince the introduction of colorimetric kits for the determination of phenylalanine (Phe) levels it has been a common practice to use the “blank” as the “zero” point of the standard curve against which all samples were calculated. The blank doesn’t contain any sample at all therefore we used our new kit (PKUMMR2000) to investigate whether the use of a real “zero - Phe” blood spot would make a difference. The kit was used with both the Millipore and the transfer protocols and yielded comparable results in all aspects. Due to the higher cost of the Millipore plate protocol the normal “transfer protocol” was used for massive screening. Results presented in this report compare the statistics obtained from 200.000 neonates screened with the “blank” used as the “zero” point of the standard curve (data from n=17.120 standard curves) versus the statistics from 20.000 neonates (data from n=1.698 standard curves) obtained with a “zero - Phe” dried blood spot. Production of the “zero” blood was made by repeated washing of red blood cells from a normal donor with normal saline and the Phe value was verified by 10 independent runs in HPLC using aquatic Phe solutions for comparison. Results show that the use of the “zero-Phe” dried blood spot leads to a lower slope (0,0078 vs. 0,0095) but improved accuracy and reproducibility especially in the low end (0-8 mg/dL Phe) while the SD at higher values is not affected. In contrast, the values and SD of the mid range controls was significantly better using the “zero-Phe” blood spot (6,102+0,85 vs. 7,05+0,97; target value: 6,0 mg/dl and 10,26+0,91 vs. 11,04+1,1; target value: 10,0 mg/dl). The new method employing the “zero-Phe” blood spot has been found to offer significant advantages especially in the low end values therefore is being normally used for routine neonatal screening for PKU in the Institute of Child Health in Greece.

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