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Background: Sapropterin has been approved as a treatment option for individuals with Phenylketonuria in the United Kingdom. Individuals are assessed as responsive to Sapropterin by a ≥30% reduction in Phenylalanine (Phe) concentrations using dried blood spot (DBS) specimens. DBS quality is critical for accurate and precise measurement of Phe. Currently, UK national guidelines for DBS specimen acceptance do not exist for patient-collected DBS specimens. We adopted evidence-based guidelines for specimen acceptance criteria and retrospectively assessed the impact of introducing these guidelines on specimen rejection rates. Methods: Laboratories were invited to audit the quality of DBS specimens routinely received for Phe monitoring using: (1) existing acceptance/rejection criteria and (2) proposed national guidelines. Results: Ten laboratories audited 2111 specimens from 1094 individuals. Using existing local guidelines, the median rejection rate was 4.0% (IQR 1.5–7.2%). This increased to 21.9% (IQR 10.0–33.0%) using the proposed guidelines. Where reason(s) for rejection were provided (n = 299); 211/299 (70.6%) of DBS specimens were too small or multi-spotted. 380 individuals had more than one sample evaluated; 231/380 (60.8%) provided specimens of acceptable quality, 37/380 (9.7%) consistently provided poor-quality DBS specimens. Conclusions: There is significant variability in the quality of patient-collected DBS specimens. If unacceptable specimens are not rejected, imprecise/inaccurate results will be used in clinical decision making. Using annual workload data for England, this equates to 12,410 incorrect results. Individuals and parents/carers should receive ongoing training in blood collection technique to ensure use of evidence-based acceptability criteria does not cause undue distress from increased sample rejection rates. [ABSTRACT FROM AUTHOR]

Background: Quantification of plasma amino acids is key to the diagnosis of inherited defects of amino acid synthesis, catabolism and transport, many of which present as clinical emergencies. The utility of this test is limited by the long analysis time and subsequent inability of laboratories to provide results in real-time. Traditionally, analysis has been performed by ion exchange chromatography (IEC) but recently there has been a move towards liquid chromatography tandem mass spectrometry (LC-MS/MS) which provides the potential for faster analysis. However, the necessity to derivatise the sample and/or utilise an ion-pair reagent, combined with lack of commercially available stable isotope internal standards (IS) has prevented laboratories fully exploiting the benefits of this methodology. We describe an underivatised LC-MS/MS method enabling patient results to be reported with an improved turnaround time (<1 h). Methods: Methanolic IS was added to plasma (10 μL) to precipitate protein. Following centrifugation amino acids were analysed by LC-MS/MS using selected reaction monitoring (SRM) for each analyte and corresponding IS. Results: Patient samples (n = 57) and external quality assessment (EQA) material (n = 11) were analysed and results compared with IEC. Comparable accuracy and precision were obtained with 15-min analysis time. Conclusions: This method enables the analysis of a clinically comprehensive amino acid profile without the need for derivatisation/ion-pair reagents and benefitting from improved analytical quantitation through multipoint calibration and use of stable isotope IS. The analysis time is fast in comparison to IEC, improves efficiency of laboratory workflow and enables stat analysis of clinically urgent samples. [ABSTRACT FROM AUTHOR]

Analysis of blood phenylalanine is central to the monitoring of patients with phenylketonuria (PKU) and age‐related phenylalanine target treatment‐ranges (0‐12 years; 120‐360 μmol/L, and >12 years; 120‐600 μmol/L) are recommended in order to prevent adverse neurological outcomes. These target treatment‐ranges are based upon plasma phenylalanine concentrations. However, patients are routinely monitored using dried bloodspot (DBS) specimens due to the convenience of collection. Significant differences exist between phenylalanine concentrations in plasma and DBS, with phenylalanine concentrations in DBS specimens analyzed by flow‐injection analysis tandem mass spectrometry reported to be 18% to 28% lower than paired plasma concentrations analyzed using ion‐exchange chromatography. DBS specimens with phenylalanine concentrations of 360 and 600 μmol/L, at the critical upper‐target treatment‐range thresholds would be plasma equivalents of 461 and 768 μmol/L, respectively, when a reported difference of 28% is taken into account. Furthermore, analytical test imprecision and bias in conjunction with pre‐analytical factors such as volume and quality of blood applied to filter paper collection devices to produce DBS specimens affect the final test results. Reporting of inaccurate patient results when comparing DBS results to target treatment‐ranges based on plasma concentrations, together with inter‐laboratory imprecision could have a significant impact on patient management resulting in inappropriate dietary change and potentially adverse patient outcomes. This review is intended to provide perspective on the issues related to the measurement of phenylalanine in blood specimens and to provide direction for the future needs of PKU patients to ensure reliable monitoring of metabolic control using the target treatment‐ranges. [ABSTRACT FROM AUTHOR]

While the early and asymptomatic recognition of treatable conditions offered by newborn screening confers clear health benefits for the affected child, the clinical referral of patients with screen positive results can cause significant harm for some families. The use of pivalate-containing antibiotics and more recently the inclusion of neopentanoate as a component within moisturising creams used as nipple balms by nursing mothers can result in a significant number of false positive results when screening for isovaleric acidaemia (IVA) by measuring C5 acylcarnitine. A recent survey conducted within centres from nine countries indicated that this form of contamination had been or was a significant confounding factor in the detection of IVA in seven of the nine who responded. In three of these seven the prominent cause was believed to derive from the use of moisturising creams and in another three from antibiotics containing pivalate; one country reported that the cause was mixed. As a result, four of these seven centres routinely perform second tier testing to resolve C5 isobars when an initial C5 result is elevated, and a fifth is considering making this change within their national programme. The use of creams containing neopentanoate by nursing mothers and evolving patterns in the prescription of pivalate-containing antibiotics during pregnancy require those involved in the design and operation of newborn screening programmes used to detect IVA and the doctors who receive clinical referrals from these programmes to maintain an awareness of the potential impact of this form of interference on patient results., Competing Interests: Conflicts of InterestThe authors declare no conflict of interest., (© 2018 by the authors.)