How Long are Residual Newborn Screening Specimens Useful for Retesting when Stored in Suboptimal and Uncontrolled Conditions of Temperature and Humidity?

Abstract Residual DBS specimens from newborns diagnosed with Phenylketonuria, Congenital Hypothyroidism, Cystic Fibrosis, Congenital Adrenal Hyperplasia and Galactosemia collected within 1995-2018, stored in cardboard boxes at ambient temperature in uncontrolled conditions, were retested for phenylalanine (Phe), thyrotropin (TSH), immunoreactive trypsinogen (IRT), total galactose (TGal) and 17-hydroxyprogesterone (17OHP), to demonstrate how long are they stable in these conditions and useful to reconfirm a previous abnormal result. Recovery percentage at retesting and qualitative interpretation regarding the current cutoff were evaluated. Phe, TSH and IRT recoveries showed decreasing trends along time. Phe recovery was 64 % after 2-years storage; TSH decayed rapidly recovering 47.3 % at 1-year, while IRT showed recoveries of 60 % at 1-year. Although 17OHP recovery presented a wide variation of results, a decaying trend was also found. Results suggest 17OHP is more stable than TSH and IRT, as supported by recoveries > 71 % when stored ≤ 2-years. TGal recovery presented an erratic behavior, so that it was not possible to estimate expected concentrations as a function of storage time. TGal recoveries above 100 % were found in UDP-galactose-4-epimerase and galactose-1-phosphate uridyltransferase deficiencies, evidencing possible galactose liberation from other sources. These results make a very valuable contribution for programs storing residual DBS in uncontrolled conditions.

Newborn Screening for Phenylketonuria: Latin American Consensus Guidelines

Abstract Newborn screening (NBS) for phenylketonuria in Latin America gave its first step in an organized way 3 decades ago when the first national NBS program was implemented in Cuba. From then onward, it experienced a slow but continuous growing, being currently possible to find from countries where no NBS activity is known to several countries with consolidated NBS programs. This complex scenario gave rise to a great diversity in the criteria used for sample collection, selection of analytical methods, and definition of cutoff values. Considering this context, a consensus meeting was held in order to unify such criteria, focusing the discussion in the following aspects—recommended blood specimens and sample collection time; influence of early discharge, fasting, parenteral nutrition, blood transfusions, extracorporeal life support, and antibiotics; main causes of transient hyperphenylalaninemias; required characteristics for methods used in phenylalanine measurement; and finally, criteria to define the more appropriate cutoff values.

Determinación colorimétrica de proteínas glicadas en sangre entera. Recolección de muestras en papel de filtro. Valores de referencia en niños / Colorimetric determination of glycated whole blood protein collection of samples on filter paper. Reference values on children

Las proteínas glicadas en sangre entera (PGSE) constituyen un parámetro que permite el seguimiento del control glucémico en pacientes con Diabetes mellitus, ofreciendo información de la glucemia promedio en los dos a tres meses previos. En el presente trabajo se llevó a cabo la puesta a punto del método colorimétrico del ácido 2-tiobarbitúrico (ATB) para medir PGSE, recolectada en papel de filtro. El fundamento del método consiste en la conversión del glúcido unido a la proteína a 5-hidroximetilfurfural (5-HMF) por calentamiento a 100 C en presencia de ácido oxálico. Por reacción entre 5-HMF y ATB se forma un compuesto coloreado que puede cuantificarse a 443 nm. Se estableció una comparación de los resultados de PGSE con HbA, medida por cromatografía de intercambio iónico (r=0,505) y por método colorimétrico del ATB (r=o,948). Este último estudio comparativo permite demostrar que las PGSE están constituidas en un 70-90% por HbA1, correspondiendo el porcentaje restante a proteínas séricas glicadas. También se estudió una población infantil normal obteniéndose un intervalo de referencia para PGSE de 41-87 nmol fructuosa/10mg proteínas; y una población infantil diabética, tipo I, observándose que el método en estudio permite diferenciar claramente los pacientes diabéticos compensados de aquellos no compensados. Los C.V.% intra e interensayo para estándares fueron inferiores a 4,3 y 5,3% respectivamente, en tanto para muestras fueron de 4,5 y 6,5% respectivamente. Además se observó que el método es sensible, barato y presenta ventajas respecto de otros métodos, ya que elimina la interferencia de hemoglobinopatías, aductos de Hb no glicadas y forma aldimina inestable; y no es influido por el pH y la temperatura