Evaluation of the Genetic Screening Processor for the Performance of Newborn Screening Tests

Abstract The collection of dried blood spots (DBSs) on filter paper has been a powerful tool in newborn screening (NBS) programs and in other fields. However, filter paper has been associated with some level of imprecision due to the filter paper matrix effect. In order to minimize measurement variations, these interferences should be evaluated by NBS assays. The aim of this study is to evaluate the performance of genetic screening processor (GSP) equipment in comparison with a widely used AutoDELFIA and to discuss the limitations and advantages of this new technology in NBS. We evaluated the performance of 3 NBS assays in DBS using GSP in comparison with AutoDELFIA. To determine the inaccuracy and the intra-assay precision, a comparative study and a replication experiment were performed. In the comparative study, human thyroid-stimulating hormone (hTSH) assay showed the highest correlation coefficient, followed by 17α-OH-progesterone and immunoreactive trypsinogen (IRT) assays. The results of the present study suggest that the GSP equipment and kits are suitable for implementation and have acceptable performance for NBS routine. Genetic screening processor assay tends to underestimate hTSH and IRT concentrations in the clinically relevant range when compared to AutoDELFIA assays. More studies are necessary to reevaluate cutoff values. Furthermore, the equipment has advantages when compared with AutoDELFIA, such as methodology with more specificity, reduction in the processing time, and randomized routine. This helps promoting faster dynamic technical processes and faster report generation.

Determinação da acurácia do método qualitativo da medida da atividade da glicose-6-fosfato desidrogenase / Determination of the accuracy of the measurement method for dehydrogenase activity

A deficiência de glicose-6-fosfato desidrogenase (G6PD) é um problema de saúde pública que afeta aproximadamente 400 milhões de pessoas no mundo. No mercado, existem vários métodos que medem a atividade da G6PD. Os objetivos deste estudo foram determinar a acurácia do método de Brewer frente a um padrão de referência e estimar a prevalência de deficiência de G6PD na amostra. Foi realizado um estudo transversal de grupo de pacientes internados no HCPA com icterícia a esclarecer, no período de junho de 2004 a maio de 2005. Amostras foram processadas pelo método de Brewer e pelo método de Normalização da Hemoglobina, o qual foi usado como padrão ouro. Foi analisado para atividade da G6PD um total de 173 pacientes. A idade variou de 1 dia a 82 anos, sendo que 66 por cento da amostra possuía até 15 dias de vida. A atividade média e o desvio padrão da G6PD na amostra analisada foi de 17.67± 5,66 U/gHb. A freqüência estimada, pelo padrão ouro, da deficiência de G6PD, foi de 13 (7,7 por cento) pacientes com deficiência parcial ou total, e pelo método de Brewer foi de 14 (8,67 por cento). A sensibilidade do método de Brewer comparada com o método quantitativo da Normalização da Hemoglobina foi de 92,8 por cento e a especificidade foi de 98,7 por cento. A deficiência de G6PD é prevalente em nosso meio. Testes de baixo custo, tais como o teste de Brewer, podem ser utilizados como testes de triagem desta deficiência, principalmente no monitoramento de recém-nascidos que estão sob o risco de desenvolver icterícia neonatal.

Glucose-6-phosphate dehydrogenase deficiency (G6PD) is a public health problem which affects about 400 millions of people all over the world. Some methods that measure the activity of G6PD have already been developed. Thus, the aim of this study was to evaluate the accuracy of the Brewer's method compared with a standard reference and estimate the prevalence of G6PD deficiency in the sample. A cross-sectional study of a group of patients in HCPA presenting with jaundice was carried out from June 2004 to May 2005. Samples were processed by the metahaemoglobin reduction test (Brewer's method) and by the method of Haemoglobin Normalization, which was used as the standard reference. A total of 173 patients were analyzed for G6PD activity. The ages varied from one day to 82 years old with 66 percent of the sample being less than 16 days old. The mean activity and standard deviation of G6PD for the analyzed sample was 17.67 ± 5.66 U/gHb. The estimated frequencies of G6PD deficiency for the standard reference and Brewer's method were 13 (7.7 percent) subjects (total or partial deficiency) and 14 (8.67 percent), respectively. When the Brewer's method was compared with the quantitative method of Hemoglobin Normalization, it showed a sensitivity of 92.8 percent and specificity of 98.7 percent. As G6PD deficiency predominates in our society, low cost tests, such as the Brewer's test can be used for screening this deficiency, mainly to monitor newborn babies who are at risk of developing jaundice.

Molecular characterization of glucose-6-phosphate dehydrogenase deficiency in patients from the southern Brazilian city of Porto Alegre, RS

Glucose-6-phosphate dehydrogenase (G6PDH; EC 1.1.1.49) deficiency is one of the most common human enzymopathies throughout the world. Although most affected individuals are asymptomatic, there is a risk of neonatal jaundice and acute hemolytic anemia which can be triggered by infection, some pharmaceuticals and, in older individuals, eating fava beans. We characterized the molecular basis of G6PDH deficiency in a sample of 348 adults from Porto Alegre (population about 1.5 million), the capital of the southernmost Brazilian state of Rio Grande do Sul. Genomic DNA was extracted from peripheral blood leukocytes. We studied the three G6PDH mutations that appear to be the most frequent in Southern Brazil, the G202A and A376G A minus (A-) variants and the C563T Mediterranean (Med) variant. From July 2004 to October 2005, 348 patients (162 Females plus 186 males, age range 0 to 82 years) from Porto Alegre were referred to our laboratory for G6PDH analysis, 36 (9.7 percent) of which showed deficient G6PDH activity. These 36 patients and 34 randomly-selected non-deficient control individuals were submitted to molecular analysis which revealed a predominance of G6PDH A- allele among the deficient patients. The prevalence of the G6PDH A- variant agrees with its distribution among the ethnic groups that colonized RS, especially those of African, Portuguese, Spanish, and Italian origin.