Schonfeld D J, Cullen M R, Rainey P M, Berg A T, Brown D R, Hogan J C, Turk D S, Rude C S, Cicchetti D V
Department of Pediatrics, Yale University School of Medicine, New Haven, CT 06520-8064.
Pediatrics. 1994 Aug;94(2 Pt 1):174-9.
To assess the false positive rate of blood lead (BPb) determinations on samples obtained by fingerstick from children screened in an urban clinic.
From a single fingerstick (N = 1573), blood was collected in a capillary tube for determining lead concentration (CPb) by graphite furnace and an additional sample was absorbed onto a filter paper for determining lead concentration (FPb) by atomic absorption spectrophotometry with Delves cup. Zinc protoporphyrin (ZPP) was measured immediately and a confirmatory venous lead (VPb) specimen was obtained at the same visit if the ZPP was > or = 35 micrograms/dL (0.6 mumol/L); children with either a CPb or FPb > or = 15 micrograms/dL (0.7 mumol/L) were later recalled for determining VPb.
For the 172 children who had a VPb on the same day as the screening tests, the false positive rates (95% confidence intervals) at a lead threshold of 15 micrograms/dL (0.7 mumol/L) were: CPb, 13.5% (6.7-20.3); FPb, 19.1% (11.8-26.4). Analyses using all 679 screens with a paired venous specimen (mean delay between screen and venous testing = 30 days) yielded much higher false positive rates (CPb, 31.3%; FPb, 46.0%).
Screening for lead poisoning is feasible within an urban pediatric clinic by direct measurement of lead concentration in blood samples obtained by fingerstick. The false positive rate that can be obtained is acceptable given the precision of measuring BPb concentration. Practitioners using a staged screening protocol may incorrectly attribute a higher false positive rate to the screening tests, when much of the error may be due to the temporal variability of BPb resulting from both biologic variability in BPb concentration and intermittent exposures.
评估在城市诊所接受筛查的儿童中，通过手指采血获得的样本进行血铅（BPb）测定的假阳性率。
从单次手指采血（N = 1573）中，采集血液至毛细管中，通过石墨炉测定铅浓度（CPb），并采集额外样本吸附于滤纸上，通过带有德尔夫斯杯的原子吸收分光光度法测定铅浓度（FPb）。立即测量锌原卟啉（ZPP），如果ZPP≥35微克/分升（0.6微摩尔/升），则在同一次就诊时采集确认性静脉血铅（VPb）样本；CPb或FPb≥15微克/分升（0.7微摩尔/升）的儿童随后被召回测定VPb。
对于在筛查测试当天进行VPb测定的172名儿童，铅阈值为15微克/分升（0.7微摩尔/升）时的假阳性率（95%置信区间）为：CPb，13.5%（6.7 - 20.3）；FPb，19.1%（11.8 - 26.4）。使用所有679次筛查并配对静脉样本（筛查与静脉检测之间的平均间隔时间 = 30天）进行分析，得出的假阳性率更高（CPb，31.3%；FPb，46.0%）。
通过直接测量手指采血获得的血样中的铅浓度，在城市儿科诊所内筛查铅中毒是可行的。鉴于测量BPb浓度的精度，所获得的假阳性率是可以接受的。采用分阶段筛查方案的从业者可能会错误地将较高的假阳性率归因于筛查测试，而实际上许多误差可能是由于BPb浓度的生物学变异性和间歇性暴露导致的BPb时间变异性。
