Dataset Information

Monitoring phenylalanine concentrations in the follow-up of phenylketonuria patients: An inventory of pre-analytical and analytical variation.

ABSTRACT:

Background

Reliable measurement of phenylalanine (Phe) is a prerequisite for adequate follow-up of phenylketonuria (PKU) patients. However, previous studies have raised concerns on the intercomparability of plasma and dried blood spot (DBS) Phe results. In this study, we made an inventory of differences in (pre-)analytical methodology used for Phe determination across Dutch laboratories, and compared DBS and plasma results.

Methods

Through an online questionnaire, we assessed (pre-)analytical Phe measurement procedures of seven Dutch metabolic laboratories. To investigate the difference between plasma and DBS Phe, participating laboratories received simultaneously collected plasma-DBS sets from 23 PKU patients. In parallel, 40 sample sets of DBS spotted from either venous blood or capillary fingerprick were analyzed.

Results

Our data show that there is no consistency on standard operating procedures for Phe measurement. The association of DBS to plasma Phe concentration exhibits substantial inter-laboratory variation, ranging from a mean difference of -15.5% to +30.6% between plasma and DBS Phe concentrations. In addition, we found a mean difference of +5.8% in Phe concentration between capillary DBS and DBS prepared from venous blood.

Conclusions

The results of our study point to substantial (pre-)analytical variation in Phe measurements, implicating that bloodspot Phe results should be interpreted with caution, especially when no correction factor is applied. To minimize variation, we advocate pre-analytical standardization and analytical harmonization of Phe measurements, including consensus on application of a correction factor to adjust DBS Phe to plasma concentrations.

SUBMITTER: Coene KLM

PROVIDER: S-EPMC7932865 | biostudies-literature |

REPOSITORIES: biostudies-literature

ACCESS DATA

Similar Datasets

Project description:BACKGROUND: Metabolic control and dietary management of patients with phenylketonuria (PKU) are based on single blood samples obtained at variable intervals. Sampling conditions are often not well-specified and intermittent variation of phenylalanine concentrations between two measurements remains unknown. We determined phenylalanine and tyrosine concentrations in blood over 24 hours. Additionally, the impact of food intake and physical exercise on phenylalanine and tyrosine concentrations was examined. Subcutaneous microdialysis was evaluated as a tool for monitoring phenylalanine and tyrosine concentrations in PKU patients. METHODS: Phenylalanine and tyrosine concentrations of eight adult patients with PKU were determined at 60 minute intervals in serum, dried blood and subcutaneous microdialysate and additionally every 30 minutes postprandially in subcutaneous microdialysate. During the study period of 24 hours individually tailored meals with defined phenylalanine and tyrosine contents were served at fixed times and 20 min bicycle-ergometry was performed. RESULTS: Serum phenylalanine concentrations showed only minor variations while tyrosine concentrations varied significantly more over the 24-hour period. Food intake within the patients' individual diet had no consistent effect on the mean phenylalanine concentration but the tyrosine concentration increased up to 300% individually. Mean phenylalanine concentration remained stable after short-term bicycle-exercise whereas mean tyrosine concentration declined significantly. Phenylalanine and tyrosine concentrations in dried blood were significantly lower than serum concentrations. No close correlation has been found between serum and microdialysis fluid for phenylalanine and tyrosine concentrations. CONCLUSIONS: Slight diurnal variation of phenylalanine concentrations in serum implicates that a single blood sample does reliably reflect the metabolic control in this group of adult patients. Phenylalanine concentrations determined by subcutaneous microdialysis do not correlate with the patients' phenylalanine concentrations in serum/blood.

Project description:In phenylketonuria (PKU), a previous intervention study assessing the patients ability to tolerate fruits and vegetables containing phenylalanine 76-100 mg/100 g without limit or measurement, found that an extra 50 mg/day phenylalanine, but not 100 mg/day, was tolerated from these fruits and vegetables. In a further 6-month extension study, we examined the effect of the 'free' use of this group of fruits and vegetables on blood phenylalanine control. For 6 months, the patients ate fruits and vegetables containing phenylalanine 76-100 mg/100 g without limit or measurement. Three-day diet diaries and the patients' weights were collected monthly. Blood phenylalanine spots were collected weekly aiming for blood phenylalanine levels <360 μmol/L. Retrospective blood phenylalanine was collected 6 months pre-trial. All 16 patients (69% females) from the intervention study took part in the extension study. Most of the patients (n = 14/16) had classical PKU with a median age of 10.5 years (range: 6-13). There was no statistically significant difference in the median blood phenylalanine pre-study (270, range: 50-760 μmol/L) compared to the 6-month extension study (250, range: 20-750 μmol/L) (p= 0.4867). The patients had a median of 21 and 22 bloodspots, pre- and post-trial, respectively. In the extension study, the patients had an actual mean intake of 11 g/day (4-37) natural protein and 65 g/day (60-80) protein equivalent from a protein substitute. The mean phenylalanine intake was 563 mg/day (200-1850) with only 19 mg/day (0-146) phenylalanine from fruits and vegetables containing phenylalanine 76-100 mg/100 g. The weight z-scores remained unchanged (1.52 vs. 1.60, p = 0.4715). There was no adverse impact on blood phenylalanine control when fruits and vegetables containing phenylalanine 76-100 mg/100 g were eaten without limit or measurement. However, the fruits and vegetable portion sizes eaten were small (60 g/week). Further longitudinal work is necessary to examine the 'free' use of fruits and vegetables containing phenylalanine 76-100 mg/100 g on metabolic control in patients with PKU.