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One
Page Summary
Blood
Lead Laboratory Reference System (BLLRS)
Background
Despite the good news that the average level of lead in Americans' blood has decreased from 12.8 to 2.8
µg/dL (JAMA 1994:272;284-291), lead poisoning remains the leading environmental threat to children in the
United States, especially poor children, minority children, and children living in inner cities.
Data gathered through the National Health and Nutritional Examination Survey, 1988-1991,
indicates that
1.7 million children aged 1 to 5 years have blood lead levels of 10 µg/dL or greater. These levels are high
enough to be a health concern under CDC's 1991 guidelines for preventing lead poisoning.
As understanding of the adverse health effects of lead poisoning has increased, the acceptable level of lead in blood has decreased and the need for accurate and precise blood lead measurements has
increased.
To help laboratories
ensure their blood lead measurements are of the highest quality, in
1990 CDC began the Blood Lead Laboratory Reference System (BLLRS).
What is the Blood Lead
Laboratory Reference System?
BLLRS is a CDC
standardization program designed to improve the overall quality of
laboratory measurements of blood lead.
DLS sends blood lead
reference materials with known values to laboratories that participate in
BLLRS.
Laboratories can use these materials for several purposes, the most
important being to ensure that their measurements of blood lead are
accurate and precise. About 270 laboratories
worldwide are enrolled.
Participation in BLLRS
is voluntary and free of charge.
Primary Goals of
BLLRS:
Why should
laboratories participate in BLLRS?
Physicians diagnose
childhood lead poisoning on the basis of blood tests performed in clinical
laboratories. Results of these tests should be the
same regardless of when, how, or where the tests are done. Therefore, a
method of standardizing measurements is essential.
A standardization
method that involves laboratory consensus is not adequate for two reasons:
-
Consensus values may reflect the biases of a particular analytic method or calibration practice.
-
Accurate measurements became critical when researchers recognized that blood lead levels as low as 10
µg/dL are dangerous to children.
How BLLRS Works
Once each quarter
participating laboratories receive three or four pools of blood containing
a known amount of lead. Participating laboratories analyze the blood pools
using their usual methods and test their results against the target values
given by CDC.
Laboratories
do not pass or fail under BLLRS, and results are not used
for accreditation or certification.
Every other quarter,
CDC ships specimens without providing the target values. After analyzing
those samples, laboratories send their results to CDC. The BLLRS
laboratory then compares all the results with CDC's target
results.
Next DLS sends a report
to participating laboratories showing (for each pool) the number of
laboratories that participated in the test, the number of test results,
the mean value of all test results, the mean laboratory bias, the standard
deviation, and CDC's target value. No single laboratory is identified in
the report.
The value of this BLLRS
report is that it allows laboratories to assess their own test results
relative to those of other participating laboratories and relative to the
CDC-assigned target results.
How Laboratories Can Use
BLLRS
Samples
Each
participating laboratory primarily uses CDC's blood lead reference
materials to ensure its measurements of blood lead are accurate
and precise.
However,
participating laboratories can also use these blood lead reference
materials with known values for several other purposes:
-
To
verify calibrations.
-
To
trouble-shoot analytical problems.
-
To set up quality-assurance or quality-control programs.
-
To
compare various laboratory methods.
-
To
conduct research and development.
Accurate Methods for
Measuring Blood Lead
Because the level of concern for childhood lead poisoning is
now recognized as 10 µg/dL rather
than 25 µg/dL, the erythrocyte protoporphyrin test is no longer adequate
for finding children adversely affected by lead.
A highly accurate (low
bias) method for measuring blood lead is the isotope dilution-mass
spectroscopy technique used by the National Institute of Standards
and Technology to establish accurate target values for its Standard
Reference Material: Lead in Bovine Blood (SRM 995a, available by calling
301(975-6776).
CDC uses a similar
method, inductively coupled plasma-isotope dilution-mass spectroscopy
analysis, to determine target values for BLLRS
samples and other quality-control materials.
Links to Other Blood Lead Proficiency and
Testing Programs
NY State Blood Lead Proficiency Program
NIST SRM 955b
CAP Lead Proficiency Program
For
questions or comments, click here
Contact NCEH
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