Zaffanello Marco, Zamboni Giorgio, Maffeis Claudio, Tatò Luciano
Regional Centre of Neonatal Screening for Inborn Erros of Metabolism and Department of Paediatrics, University of Verona, Verona, Italy.
J Med Screen. 2003;10(4):181-3. doi: 10.1258/096914103771773276.
To investigate the predictive role that neonatal birth parameters of positive newborns at phenylketonuria (PKU) screening have on false-positive and positive results. We reviewed 195 newborns (115 males and 80 females) that had false-positive results between 1998 and 2001. A total of 4386 randomly selected neonates (2191 males and 2195 females) who tested normal at the first investigation in the same period, were used as negative-controls. A total of 38 PKU neonates (17 males and 21 females) diagnosed between 1990 and 2001 were used as positive-controls.
Phenylalanine concentration was measured with a fluorometric multitask plate counter Wallac 1420 VICTOR F (Perkin Elmer, Finland) and the fluorescent ninhydrine method (EG&G Wallac neonatal phenylalanine kit) using a recall cut-off level >120 micromol/l (2 mg/dl) of phenylalanine on dried blood spots. A multivariate logistic regression analysis was performed to evaluate the predictive role that body parameters (sex, gestational age, parity, weight, length and head circumference) of positive newborns at PKU screening had on false-positive and positive results at recall PKU tests.
The risk of false-positive results is higher (~48%) in females than in males. Moreover, for each 100g of body weight reduction, the risk of false positive is around 4.2% higher. The risk of confirmation increased by 39% per week of gestational age.
In conclusion, our results suggest that preterm or low-birth-weight neonates recalled at the first investigation are more likely to be due to false-positives, whereas the risk of confirmation is higher in at-term neonates. By implication, the phenylalanine cut-off value for premature or low-body-weight infants could be higher.
研究苯丙酮尿症（PKU）筛查呈阳性的新生儿出生参数对假阳性和阳性结果的预测作用。我们回顾了1998年至2001年间195例假阳性结果的新生儿（115例男性和80例女性）。同期随机选取4386例首次检测正常的新生儿（2191例男性和2195例女性）作为阴性对照。1990年至2001年间确诊的38例PKU新生儿（17例男性和21例女性）作为阳性对照。
使用荧光多任务酶标仪Wallac 1420 VICTOR F（芬兰珀金埃尔默公司）和荧光茚三酮法（EG&G Wallac新生儿苯丙氨酸试剂盒）测定干血斑中苯丙氨酸浓度，召回检测时苯丙氨酸的截断水平>120微摩尔/升（2毫克/分升）。进行多因素逻辑回归分析，以评估PKU筛查呈阳性的新生儿身体参数（性别、胎龄、产次、体重、身长和头围）对召回PKU检测时假阳性和阳性结果的预测作用。
女性假阳性结果的风险更高（约48%），高于男性。此外，体重每减轻100克，假阳性风险约高4.2%。胎龄每增加一周，确诊风险增加39%。
总之，我们的结果表明，首次检测时被召回的早产或低体重新生儿更可能是假阳性，而足月儿确诊的风险更高。这意味着，早产或低体重婴儿的苯丙氨酸截断值可能更高。
