Diurnal variation of phenylalanine and tyrosine concentrations in adult patients with phenylketonuria: subcutaneous microdialysis is no adequate tool for the determination of amino acid concentrations

Table 4 Correlation of phenylalanine and tyrosine concentrations and phenylalanine: tyrosine concentration ratio between different types of samples

	Real time		Delay 1 h		Delay 2 h
Variable	r	p	r	p	r	p
Correlation between serum and dried blood
Phe	.50	.01
Tyr	.96	< .001
[Phe]/[Tyr]	.96	< .001
Correlation between serum and microdialysate
Phe	-.11	.64	-.15	.48	-.24	.25
Tyr	.54	.01	.23	.28	.04	.84
[Phe]/[Tyr]	.76	< .001	.52	.01	.28	.18

Phe = phenylalanine; Tyr = tyrosine; [Phe]/[Tyr] = phenylalanine: tyrosine concentration ratio.
The correlation analysis of phenylalanine and tyrosine concentrations and of the phenylalanine: tyrosine concentration ratio ([Phe]/[Tyr]) between microdialysis fluid and serum was performed with samples taken simultaneously (“Real time”) and with microdialysate samples taken one hour (“Delay 1 h”) and two hours (“Delay 2 h”) after blood sampling. To assess the above-mentioned correlations Pearson’s correlation coefficients (r) were calculated for each patient, then transformed to Fisher-Z values (Fisher r-to-Z transformation) and averaged. Resulting mean Fisher-Z values were retransformed to r values (reversed Fisher transformation).

ISSN: 1475-2891