Investigation of the relationship between phenylalanine in venous plasma and capillary blood using volumetric blood collection devices.

Measurement of plasma and dried blood spot (DBS) phenylalanine (Phe) is key to monitoring patients with phenylketonuria (PKU). The relationship between plasma and capillary DBS Phe concentrations has been investigated previously, however, differences in methodology, calibration approach and assumptions about the volume of blood in a DBS sub-punch has complicated this. Volumetric blood collection devices (VBCDs) provide an opportunity to re-evaluate this relationship. Paired venous and capillary samples were collected from patients with PKU (n = 51). Capillary blood was collected onto both conventional newborn screening (NBS) cards and VBCDs. Specimens were analysed by liquid-chromatography tandem mass-spectrometry (LC-MS/MS) using a common calibrator. Use of VBCDs was evaluated qualitatively by patients. Mean bias between plasma and volumetrically collected capillary DBS Phe was -13%. Mean recovery (SD) of Phe from DBS was 89.4% (4.6). VBCDs confirmed that the volume of blood typically assumed to be present in a 3.2 mm sub-punch is over-estimated by 9.7%. Determination of the relationship between plasma and capillary DBS Phe, using a single analytical method, common calibration and VBCDs, demonstrated that once the under-recovery of Phe from DBS has been taken into account, there is no significant difference in the concentration of Phe in plasma and capillary blood. Conversely, comparison of plasma Phe with capillary DBS Phe collected on a NBS card highlighted the limitations of this approach. Introducing VBCDs for the routine monitoring of patients with PKU would provide a simple, acceptable specimen collection technique that ensures consistent sample quality and produces accurate and precise blood Phe results which are interchangeable with plasma Phe.

Cross-sectional audit assessing the quality of dried bloodspot specimens received by UK metabolic biochemistry laboratories for the biochemical monitoring of individuals with Phenylketonuria.

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.

Incidental Detection of Classical Galactosemia through Newborn Screening for Phenylketonuria: A 10-Year Retrospective Audit to Determine the Efficacy of This Approach.

In the UK, Classical Galactosaemia (CG) is identified incidentally from the Newborn Screening (NBS) for phenylketonuria (PKU) using an "Other disorder suspected" (ODS) pathway when phenylalanine (Phe) and tyrosine (Tyr) concentrations are increased. We aimed to determine the efficacy of CG detection via NBS and estimate the incidence of CG in live births in the UK. A survey was sent to all UK NBS laboratories to collate CG cases diagnosed in the UK from 2010 to 2020. Cases of CG diagnosed were determined if detected clinically, NBS, or by family screening, as well as age at diagnosis. Cases referred via the ODS pathway were also collated, including the final diagnosis made. Responses were obtained from 13/16 laboratories. Between 2010 and 2020, a total of 6,642,787 babies were screened, and 172 cases of CG were identified. It should be noted that 85/172 presented clinically, 52/172 were identified by NBS, and 17/172 came from family screening. A total of 117 referrals were made via the ODS pathway, and 45/117 were subsequently diagnosed with CG. Median (interquartile range) age at diagnosis by NBS and clinically was 8 days (7-11) and 10 days (7-16), respectively (Mann-Whitney U test, U = 836.5, p-value = 0.082). The incidence of CG is 1:38,621 live births. The incidence of CG in the UK is comparable with that of other European/western countries. No statistical difference was seen in the timing of diagnosis between NBS and clinical presentation based on the current practice of sampling on day 5. Bringing forward the day of NBS sampling to day 3 would increase the proportion diagnosed with CG by NBS from 52/172 (30.2%) to 66/172 (38.4%).

The association between overweight/obesity and double diabetes in adults with type 1 diabetes; a cross-sectional study.

BACKGROUND: Double Diabetes (DD), type 1 diabetes (T1DM) + insulin resistance (IR), is associated with increased risk of micro/macro-vascular complications and mortality. Obesity can contribute to the development of DD. This study explored the prevalence of overweight/obesity and their association with DD in adults with T1DM. METHODS: Cross-sectional study of consecutive adults with T1DM attending diabetes clinics in a secondary care hospital (January-November 2019). Estimated glucose disposal rate (eGDR) was used as a marker of IR, and an eGDR < 8 was used to identify individuals with DD. RESULTS: One hundred seven adults with T1DM were included; female/male: 51/56; age [median (inter-quartile range): 30.0 (23-51) years]; BMI 25.4 (22.8-30.0) kg/m2. Overweight/obesity prevalence was 57/107 (53.3 %) [overweight: 30/107 (28 %); obesity: 27/107 (25.2 %)]. Compared to those with normal BMI, individuals with T1DM and overweight/obesity had longer diabetes duration; higher total daily insulin dose; and higher DD prevalence: 48/57 (84.2 %) vs. 14/50 (28 %) (p < 0.01); with similar HbA1c. BMI correlated with total daily insulin dose (rho = 0.55; p < 0.01). Individuals with DD were older, had longer duration of diabetes, higher HbA1c, and more adverse lipid profile and microalbuminuria compared to those without DD. CONCLUSIONS: Overweight/obesity is very common in adults with T1DM, and is associated with double diabetes. BMI is positively associated with total insulin dose. Double diabetes is associated with adverse cardiovascular risk profile and is also common in lean individuals with T1DM. Further research is needed to examine the impact of overweight/obesity in people with T1DM and whether weight loss in this population can improve diabetes-related outcomes.

Infantile hypercalcaemia type 1: a vitamin D-mediated, under-recognised cause of hypercalcaemia.

SUMMARY: A 33-year-old gentleman of Egyptian heritage presented with a 21 years history of unexplained and recurrent hypercalcaemia, nephrolithiasis, nephrocalcinosis, and myocarditis. A similar history was also found in two first-degree relatives. Further investigation into the vitamin D metabolism pathway identified the biochemical hallmarks of infantile hypercalcaemia type 1 (IIH). A homozygous, likely pathogenic, variant in CYP24A1 was found on molecular genetic analysis confirming the diagnosis. Management now focuses on removing excess vitamin D from the metabolic pathway as well as reducing calcium intake to achieve serum-adjusted calcium to the middle of the reference range. If undiagnosed, IIH can cause serious renal complications and metabolic bone disease. LEARNING POINTS: Infantile hypercalcaemia type 1 (IIH) is an autosomal recessive disorder characterised by homozygous mutations in the CYP24A1 gene that encodes the 24-hydroxylase enzyme used to convert active vitamin D metabolites such as 1,25-(OH)2-vitamin D into their inactive form. IIH should be questioned in individuals presenting with a history of unexplained hypercalcaemia, especially if presenting from childhood and/or where there is an accompanying family history of the same in first and/or second degree relatives, causing complications such as nephrocalcinosis, pericarditis, and calcium-based nephrolithiasis. Associated biochemistry of IIH is persistent mild to moderate hypercalcaemia, normal or raised 25-(OH)-vitamin D and elevated 1,25-(OH)2-vitamin D. An elevated ratio of 25-(OH)-vitamin D to 24,25-(OH)2-vitamin D can be a useful marker of defects in the 24-hydroxylase enzyme, whose measurement can be facilitated through the supra-regional assay service. Management should focus on limiting the amount of vitamin D introduced into the body either via sunlight exposure or supplementation in addition to calcium dietary restriction to try and maintain appropriate calcium homeostasis.

Screening for valve disease in patients with hyperprolactinaemia disorders prescribed cabergoline: a service evaluation and literature review.

OBJECTIVES: The indication for screening for valvular heart disease in patients taking cabergoline is based on evidence from patients with Parkinson's disease on high-dose medication. However, current patients take much lower doses for indications such as hyperprolactinaemia disorders. Contemporary guidelines for echocardiogram monitoring in patients taking cabergoline are conflicting. This study aimed to review current clinical practice in our area regarding echocardiographic screening and to review the literature examining the evidence of valvular heart disease in patients taking lower dose cabergoline. METHODS: This was a retrospective study of all patients with hyperprolactinaemia disorders prescribed cabergoline in a single UK NHS health board between January 2014 and July 2015. The proportion of patients receiving baseline and follow-up echocardiograms was recorded. A review of the published literature was carried out using the databases EMBASE and Medline to examine the current evidence for the effect cabergoline has on cardiac valves in patients treated for hyperprolactinaemia disorders. RESULTS: The mean age was 51.7 ± 16.5 years with a 64.4% female predominance. The mean duration of therapy was 5.9 years ± 4.1 years. Of the total cohort (n = 45), two (4.4%) patients had an initial baseline echocardiogram and five (13.2%) had follow-up echocardiograms every 24 months. Of the 25 articles identified, 12 showed no clinically significant evidence of valvular dysfunction in the cabergoline group groups. Of the remaining 13 articles, evidence for valvular changes was confined to high cumulative dose cabergoline patients and there was only one confirmed case of 'cabergoline associated valvulopathy' described. CONCLUSIONS: Clinically significant valvular dysfunction is uncommon and generally only reported in high cumulative dose treatment groups. We propose that clearer national guidelines are required and that echocardiogram screening be reserved for patients who are high risk, are taking a high weekly dose (≥2 mg cabergoline weekly) or high cumulative dose.