PEDIATRICS Vol. 103 No. 4 April 1999, p. e51
Received May 18, 1998; accepted Oct 19, 1998.
From the Department of Pediatrics, Dartmouth Medical School, Hanover, New Hampshire.
Background. Recent statements from the American Academy of Pediatrics and Centers for Disease Control and Prevention recommend diagnostic venous blood lead testing within 90 days of a marginally elevated screening test (10-14 µg/dL).
Objective. To evaluate the ability of a marginally
elevated capillary (CScr) or venous (VScr) blood lead screening test to
predict venous diagnostic (VPb) blood lead (taken within 90 days of the
screening test) that would prompt environmental evaluation (
20
µg/dL).
Design. Population-based follow-up study comparing CScr and VScr with VPb drawn within 90 days of the screening sample. This study population was drawn from all children aged 0 to 4 years who were screened in Worcester County, Massachusetts, and Providence County, Rhode Island, with CScr and VScr during calendar year 1994.
Outcome Measures. To evaluate predictive validity, CScr
and VScr were correlated with VPb. CScr, VScr, and VPb results were
then separated into the following categories: <10, 10 to 14, 15 to 19, and
20 µg/dL. CScr and VScr categories were cross-tabulated against
VPb categories, and logistic regression analysis was used to evaluate
categorical elevations of CScr and VScr as predictors of VPb
20
µg/dL.
Results. Of 31 904 children screened with CScr, 5450 (17.1%) were elevated and 1278 were followed up with VPb within 90 days. Of 14 623 children screened with VScr, 2979 (20.4%) were
elevated and 614 were followed up with VPb within 90 days. CScr was
only weakly correlated with VPb (r = 0.39), whereas
VScr was more strongly correlated with VPb (r = 0.73). Compared with CScr <10 µg/dL, CScr in the 10 to 14 µg/dL
range did not identify a higher percentage of children with VPb
elevation in any category, and falsely misclassified as lead poisoned
some 77% of children. Compared with VScr <10 µg/dL, VScr in the 10 to 14 µg/dL range identified higher percentages of children with VPb
in the 10 to 19 µg/dL range but not with VPb
20 µg/dL, and
falsely misclassified as lead poisoned 42% of children. Compared with
screening tests <10 µg/dL, the odds of identifying a child with VPb
20 were no different from 1 for CScr of 10 to 14 µg/dL (adjusted
odds ratio 1.4 [95% confidence interval 0.3, 6.6]), CScr of 15 to 19 µg/dL (3.2 [0.7, 15.7]), or VScr of 10 to 14 µg/dL (0.9 [0.3,
3.0]). CScr and VScr in the 15 to 19 µg/dL range were associated
with significantly higher odds of having VPb
20 µg/dL when compared
with screening tests <10 µg/dL.
Conclusions. These data indicate that special diagnostic
testing within 90 days for children with CScr and VScr in the 10 to 14 µg/dL range does not result in greater identification of VPb
20.
Raising the set point for diagnostic testing to 15 µg/dL in this
sample would eliminate the unnecessary follow-up of 5162 children, of whom 3360 were falsely misclassified as having undue lead
exposure.
Key words:
lead poisoning,
screening,
diagnostic
testing,
follow-up study.
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