Table 2.

Precision or coefficient of variation (CV) reflecting phe and tyr measurement with three different methods.

		Phe			Tyr
Control level	n	Concentration (μM) mean ± SD	CV (%)	n	Concentration (μM) mean ± SD	CV (%)
Plasma-IEC	Low	20	79 ± 1	1.6%	20	61 ± 3	4.9%
High	20	403 ± 7	1.6%	20	223 ± 13	5.9%
DBS-IEC	Low	20	32 ± 2	5.9%	20	38 ± 4	9.2%
High	20	482 ± 17	3.5%	20	462 ± 23	5.1%
DBS-MS/MS	Low	20	33 ± 4	11.2%	20	33 ± 3	10.3%
High	20	371 ± 43	11.7%	20	648 ± 79	12.1%