Lead Poisoning / Trace Elements Laboratory
PT Program: Toxicology - Blood Lead and Erythrocyte Protoporphyrin
Lead Poisoning / Trace Elements
Analytes Offered
Blood Lead (BPb) | Erythrocyte Protoporphyrin (EP)
History and Evolution of NY State's Blood Lead Proficiency Testing Program
The Wadsworth Center's Lead Poisoning Laboratory was established circa1973 with federal funding. Since 1974, it has been responsible for preparing and administering the proficiency test (PT) for blood lead (BPb) for the Clinical Laboratory Evaluation Program (CLEP).
During the 1970's erythrocyte protoporphyrin (EP) was the CDC-recommended test for screening children exposed to lead. A separate proficiency test for EP was also established during the 1970's.
The introduction of the hematofluorometer (HF) in the mid-1970's presents special problems for all EP PT programs. Without a primary calibration standard, HF instruments can develop a large bias relative to the reference method for EP, the ethyl acetate extraction technique. Since the HF measures a ratio of zinc protoporphyrin (ZPP) to hemoglobin, rather than total "free" protoporphyrin that is liberated following acid extraction, it is necessary to offer a special PT category for these instruments. New York is the only PT program to distribute stabilized blood-based reference materials for the HF, specifically designed to eliminate problems from plasma fluorescence. These materials are prepared from whole blood obtained from lead-dosed goats. Plasma is removed and red blood cells are washed and re-suspended in a citrate-glycerol solution. These materials may also be used for quality control purposes by HF users. Our laboratory is one of only three nationally (together with the CDC and the Wisconsin State Laboratory of Hygiene) to provide validated EP target values for the Aviv Biomedical, Inc. RBC controls. This is achieved by maintaining master instruments calibrated to the reference ethyl acetate extraction technique.
New York State is an approved CLIA '88 PT program provider, and participation in our blood lead PT program is also accepted by the US Occupational Safety and Health Administration (OSHA) for satisfying their requirements for laboratories performing BPb. The State of California also accepts successful participation in our BPb PT program as meeting the requirements for their laboratories licensed for BPb testing.
Category Description
Toxicology - Blood Lead: Clinical laboratories performing the determination of lead in blood should apply for this subcategory. Determination of other metals, such as zinc, sodium and calcium, are included under the category of Clinical Clemistry.
Toxicology - Erythrocyte Protoporphyrin: Clinical laboratories performing determination of erythrocyte protoporphyrin by using an extraction method with a conventional fluorometer, or using a hematofluorometer, should apply for this subcategory.
Proficiency Testing Offered
(HCFA regulated analytes or tests are indicated with an asterisk).
Blood lead (BPb) *
Erythrocyte Protoporphyrin
For all tests with no available New York State proficiency test (PT):
The laboratory shall have a system for verifying the reliability and accuracy of test results;
and This verification process shall be performed at least twice each year.
The issuance of clinical laboratory permits is the responsibility of the Center's Clinical Laboratory Evaluation Program (CLEP). Successful participation in an approved proficiency testing program for BPb is also a federal (Health Care Financing Administration, HCFA) requirement under CLIA '88 for clinical laboratories performing BPb tests. In addition, current OSHA regulations require laboratories testing adults for occupational lead exposure to be approved by participation in an OSHA-approved PT program for BPb. For further information on procedures for OSHA laboratory approval, contact OSHA Salt Lake Technical Center, 1781 South 300 West, Salt Lake City, UT 84115.
Test Kit and Frequency of Mailing
Proficiency test kits consist of five specimens and are mailed three times per year.
Source of Samples
The proficiency test samples are prepared by Wadsworth Center staff from whole blood collected from lead-dosed goats. Each test event contains a series of samples containing analytes at clinically relevant concentrations. After scheduled dosing with lead acetate, whole blood pools containing elevated BPb/EP concentrations are drawn into blood bags containing potassium EDTA anticoagulant, and then transferred into additive-free evacuated glass tubes for shipment to participants. Hematofluorometry samples are processed to eliminate fluorescent artifacts by separating the erythrocytes (RBCs) from plasma, washing with normal saline and resuspending the RBCs in a citrate-glycerol solution before transfer into additive-free evacuated glass tubes and shipment to participants.
Quality Control of Samples
Quality assurance and quality control of PT materials is assessed through a program of external characterization by selected reference laboratories. This includes sample-to-sample variability by analyses for blood lead, erythrocyte protoporphyrin, and examination for fibrin clots. Control procedures are also in place to prevent contamination errors.
Sample Validation
Blood Lead
Target values for blood lead are established by a greater than 90% consensus of the referee laboratories.
Erythrocyte Protoporphyrin
Target values for EP are established by method: (a) EEP, conventional spectrofluorometry after a two-step ethyl acetate-acetic acid extraction; and (b) HEP, front-face fluorometry (Aviv hematofluorometry). Separate arrangements are in place for Helena ProtoFluor-Z (ZPP) users. For the extraction method, target values are calculated using results from all participants (excluding outliers). Target values for Aviv instruments are calculated using results from at least 10 referee laboratories and are given as µg/dL, assumed hematocrit 35, while target values for Helena ProtoFluor-Z instruments are calculated using results from all participants (excluding outliers) and are given as µmol ZPP/mol heme.
Criteria For Acceptable Performance
| Analyte | Acceptable Performance |
|---|---|
| Blood Lead (BPb) | ±4 µg/dL (values less than or equal to 40 µg/dL) or ±10% (values greater than 40 µg/dL) |
| EEP/HEP | ±6 µg/dL (values less than or equal to 40 µg/dL) or ±15% (values greater than 40 µg/dL) |
| ZPP | ±15% (µmol/mol heme) |
To achieve satisfactory performace in a single test event, participant laboratories must score 80% or greater, i.e., report 4 out of 5 PT samples within the acceptable range. Moreover, to maintain successful PT performance, participants must maintain a satisfactory score in at least two out of three consecutive test events.
Grading
Grades are determined as follows:
Number of acceptable responses for the analyte X 100 = Analyte and Test Event Score
_______________________________________
Total number of challenges for the analyte
Failure to attain an overall testing score of at leat 80% is unsatisfactory performance.
Test results will not be evaluated if the envelope postmark is after the report due date. Dates imprinted by postage meters will be accepted unless there is a United States Postal Service cancellation on the envelope. In such cases the latter will be considered the postmark date.
Notification
The laboratory is required to notify the section within five days of shipment that samples have not arrived or are unacceptable for testing. Proficiency test specimens are shipped using United Parcel Service (UPS).
Replacement Samples
The laboratory may request replacement specimens under circumstances where in routine laboratory practice the recourse in patient testing is to collect additional specimens, e.g., laboratory accident or instrument failure. Replacement specimens will be provided until the published postmark deadline.
Availability of Samples
Whole blood PT samples derived from lead dosed goats have a limited shelf life (approximately 8 weeks at 4 degrees C). For hematofluorometry, PT samples are stable for up to 6 months at 4 degrees C. Since the test samples are characterized and validated by referee laboratories at the same time they are tested by participating laboratories, with the exception of HEP/ZPP, they are not generally available outside of the regular shipping schedule. However, some BPb/EP samples with limited validation can be made available at other times.
Technical Assistance
Technical advice and information on analytical methods and collection protocols are available for blood lead, EP, urine lead and other selected trace element tests.
Proficiency Test Schedule
PT Schedule for Trace Elements, Blood Lead and EP:
- 2008 PT calendar (PDF -- 58k)
PT shipment schedules are currently available online:
Proficiency Test Report Summaries
Statistical report summaries from current and previous proficiency test events (1999-present) are also available on line as downloadable PDF documents. Please go to the Proficiency Test Event Results page.
For information on the availablity of other blood lead PT programs (or external quality assessment schemes - EQAS) worldwide, please go to the Blood Lead Proficiency Testing Programs page.
Analytical Services
For information on analytical testing available from the laboratory, please go to the Analytical Services page.