Disparities in clinical laboratory performance for blood lead analysis

Interpreting and managing blood lead levels of less than 10 microg/dL in children and reducing childhood exposure to lead: recommendations of the Centers for Disease Control and Prevention Advisory Committee on Childhood Lead Poisoning Prevention

Lead is a common environmental contaminant. Lead exposure is a preventable risk that exists in all areas of the United States. In children, lead is associated with impaired cognitive, motor, behavioral, and physical abilities. In 1991, the Centers for Disease Control and Prevention defined the blood lead level that should prompt public health actions as 10 microg/dL. Concurrently, the Centers for Disease Control and Prevention also recognized that a blood lead level of 10 microg/dL did not define a threshold for the harmful effects of lead. Research conducted since 1991 has strengthened the evidence that children's physical and mental development can be affected at blood lead levels of < 10 microg/dL. In this report we provide information to help clinicians understand blood lead levels < 10 microg/dL, identify gaps in knowledge concerning lead levels in this range, and outline strategies to reduce childhood exposures to lead. We also summarize scientific data relevant to counseling, blood lead screening, and lead-exposure risk assessment. To aid in the interpretation of blood lead levels, clinicians should understand the laboratory error range for blood lead values and, if possible, select a laboratory that achieves routine performance within +/-2 microg/dL. Clinicians should obtain an environmental history on all children they examine, provide families with lead-prevention counseling, and follow blood lead screening recommendations established for their areas. As circumstances permit, clinicians should consider referral to developmental programs for children at high risk for exposure to lead and more frequent rescreening of children with blood lead levels approaching 10 microg/dL. In addition, clinicians should direct parents to agencies and sources of information that will help them establish a lead-safe environment for their children. For these preventive strategies to succeed, partnerships between health care providers, families, and local public health and housing programs should be strengthened.

Evaluation of Blood Lead Proficiency Testing: Comparison of Open and Blind Paradigms

Background: Most proficiency testing (PT) programs operate with an open design in which clearly identified performance samples are distributed directly to participating laboratories on a shipping schedule announced in advance. In this study, we examine the effectiveness of assessing clinical laboratory performance for blood lead with an open PT by comparing its results with a double-blinded testing protocol.

Methods: Aliquots from up to 72 blood lead performance pools from the New York State Department of Health and the Wisconsin State Laboratory of Hygiene were disguised as routine patient specimens and submitted in two phases to up to 42 certified clinical laboratories for blood lead analysis. These 42 laboratories also received aliquots of the same performance samples for blood lead analysis directly from the “open” PT program provider.

Results: Data reported under blind and open strategies were scored against acceptable target ranges using the Clinical Laboratory Improvement Amendments of 1988 (CLIA ’88) criteria established for blood lead, i.e., ± 0.19 μmol/L (± 4 μg/dL) or ± 10%, whichever is greater. Performance differences between the strategies were also assessed. We found that 17.7% of all blind PT results were classified as unacceptable compared with only 4.5% of open PT results (P &lt;0.001). In phase 1, 13 of 22 laboratories (60%) exhibited a statistically significant difference (P &lt;0.05) between their blind and open PT performances, although for 6 laboratories the poorer blind performance may not necessarily have led to unsuccessful PT participation under CLIA ’88 criteria. Seven (32%) laboratories had unsuccessful aggregate performance (&lt;80%) under blind testing while maintaining successful performance in open testing. Of these seven, two had gross discrepancies motivating further investigation.

Conclusions: The data suggest that although ∼60% of clinical laboratories make special efforts to improve analytical performance on open PT samples relative to performance achieved for routine patient specimens, in most cases the differences are clinically insignificant and would not likely affect cumulative PT performance. Occasional use of blind PT may deter the inclination to treat performance samples more carefully.

Improvement in physician's office laboratory practices, 1989-1994

BACKGROUND

In 1986 and 1989, the Centers for Disease Control and Prevention sponsored institutes on Critical Issues in Health Laboratory Practice. It was noted during the institutes that physician's office laboratories were a rapidly emerging site for clinical laboratory testing, yet no comprehensive data were available regarding the practice of clinical laboratory medicine in physician's office laboratories. As a mechanism to begin addressing this void, the Centers for Disease Control and Prevention added questions on clinical laboratory practice to the National Ambulatory Medical Care Survey, a national probability sample of ambulatory care provided by office-based physicians. Data were collected for survey years 1989, 1991, 1993, and 1994.

METHODS

Each survey was conducted among a nationally representative, random sample of office-based physicians who provide ambulatory patient care. Sample physicians were enlisted using both mail and telephone contacts. Clinical laboratory data were obtained via telephone by trained field representatives. Weighted univariate and multivariate analyses were performed on responses from each of the 4 survey years. Analyses were repeated after combining survey responses from years 1989 and 1991 and 1993 and 1994 as representative of physician's office laboratory practices before and after implementation of the Clinical Laboratory Improvement Amendments of 1988 (CLIA '88) final rule in 1992.

RESULTS

Quality laboratory practice indicators showed significant increases during the study interval, with implementation of the CLIA '88 final rule in 1992 playing a pivotal role. Relative to 1992, enrollment in proficiency testing programs increased from 32.4% to 52.7% (P<.001), use of daily quality control samples increased from 79.2% to 89.0% (P<.001), and use of daily quality control with written instructions for action following a questionable quality control result (quality control with action step documentation) increased from 62.6% to 77.2% (P<.001). The presence of a medical technologist or technician in the office laboratory was also significantly and independently associated with each of the quality indicators. Although the percentage of physician's offices performing on-site testing decreased from 56% to 45% during the survey interval, overall testing volume appeared unchanged.

CONCLUSIONS

The quality of clinical laboratory practice in physician's office laboratories improved during the study interval (1989-1994) as measured by the quality indicators used in the study. The association of this improvement with implementation of the CLIA '88 final rule and the presence of a trained laboratory professional in the testing site indicate the importance of minimum practice standards and professional expertise in ensuring use of quality laboratory practices. Overall test volume appeared to be stable despite a decreased proportion of physician's offices at which on-site testing was performed.

The association between state housing policy and lead poisoning in children

OBJECTIVES

This study examined the effect of an active program of household lead paint hazard abatement, applied over 22 years, on childhood lead poisoning in Massachusetts.

METHODS

A small areas analysis was used to compare screening blood lead levels of children in Worcester County, Mass (n = 27,590), with those in Providence County, RI (n = 19,071). Data were collapsed according to census tract.

RESULTS

The percentage of children with lead poisoning (blood lead level > or = 20 micrograms/dL [Pe20]) was, on average, 3 times higher in Providence County census tracts (3.2% vs 0.9% in Worcester County census tracts, P < .0001), despite similar percentages of pre-1950s housing in both counties. The ratio of Pe20 in Providence vs Worcester County census tracts was 2.2 (95% confidence interval = 1.8, 2.7), after adjustment for differences in housing, sociodemographic, and screening characteristics. This estimate was robust to alternative regression methods and sensitivity analyses.

CONCLUSIONS

Massachusetts policy, which requires lead paint abatement of children's homes and places liability for lead paint poisoning on property owners, may have substantially reduced childhood lead poisoning in that state.

Evaluation of mycology laboratory proficiency testing

Changes over the last decade in overt proficiency testing (OPT) regulations have been ostensibly directed at improving laboratory performance on patient samples. However, the overt (unblinded) format of the tests and regulatory penalties associated with incorrect values allow and encourage laboratorians to take extra precautions with OPT analytes. As a result OPT may measure optimal laboratory performance instead of the intended target of typical performance attained during routine patient testing. This study addresses this issue by evaluating medical mycology OPT and comparing its fungal specimen identification error rates to those obtained in a covert (blinded) proficiency testing (CPT) program. Identifications from 188 laboratories participating in the New York State mycology OPT from 1982 to 1994 were compared with the identifications of the same fungi recovered from patient specimens in 1989 and 1994 as part of the routine procedures of 88 of these laboratories. The consistency in the identification of OPT specimens was sufficient to make accurate predictions of OPT error rates. However, while the error rates in OPT and CPT were similar for Candida albicans, significantly higher error rates were found in CPT for Candida tropicalis, Candida glabrata, and other common pathogenic fungi. These differences may, in part, be due to OPT's use of ideal organism representatives cultured under optimum growth conditions. This difference, as well as the organism-dependent error rate differences, reflects the limitations of OPT as a means of assessing the quality of routine laboratory performance in medical mycology.

Diagnostic testing unwarranted for children with blood lead 10 to 14 microg/dL

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 microg/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 microg/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 microg/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 microg/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 microg/dL, CScr in the 10 to 14 microg/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 microg/dL, VScr in the 10 to 14 microg/dL range identified higher percentages of children with VPb in the 10 to 19 microg/dL range but not with VPb >/=20 microg/dL, and falsely misclassified as lead poisoned 42% of children. Compared with screening tests <10 microg/dL, the odds of identifying a child with VPb >/=20 were no different from 1 for CScr of 10 to 14 microg/dL (adjusted odds ratio 1.4 [95% confidence interval 0.3, 6.6]), CScr of 15 to 19 microg/dL (3.2 [0.7, 15.7]), or VScr of 10 to 14 microg/dL (0.9 [0.3, 3.0]). CScr and VScr in the 15 to 19 microg/dL range were associated with significantly higher odds of having VPb >/=20 microg/dL when compared with screening tests <10 microg/dL.

CONCLUSIONS

These data indicate that special diagnostic testing within 90 days for children with CScr and VScr in the 10 to 14 microg/dL range does not result in greater identification of VPb >/=20. Raising the set point for diagnostic testing to 15 microg/dL in this sample would eliminate the unnecessary follow-up of 5162 children, of whom 3360 were falsely misclassified as having undue lead exposure.

Screening for Elevated Blood Lead Levels

Although recent data continue to demonstrate a decline in the prevalence of elevated blood lead levels (BLLs) in children, lead remains a common, preventable, environmental health threat. Because recent epidemiologic data have shown that lead exposure is still common in certain communities in the United States, the Centers for Disease Control and Prevention recently issued new guidelines endorsing universal screening in areas with ≥27% of housing built before 1950 and in populations in which the percentage of 1- and 2-year-olds with elevated BLLs is ≥12%. For children living in other areas, the Centers for Disease Control and Prevention recommends targeted screening based on risk-assessment during specified pediatric visits. In this statement, The American Academy of Pediatrics supports these new guidelines and provides an update on screening for elevated BLLs. The American Academy of Pediatrics recommends that pediatricians continue to provide anticipatory guidance to parents in an effort to prevent lead exposure (primary prevention). Additionally, pediatricians should increase their efforts to screen children at risk for lead exposure to find those with elevated BLLs (secondary prevention).