Clinical Chemistry - Blood Lead
Childhood lead poisoning is one of the most common pediatric health problems in the United States, even though it is entirely preventable. The persistence of lead poisoning, in light of present knowledge about the sources, pathways and prevention of lead exposure, presents a direct challenge to clinicians and public health authorities.
As a result of industrialization, lead is common in the environment. It has no known physiologic value and children are particularly susceptible to its toxic effects. Most poisoned children have no apparent symptoms and many cases go undiagnosed and untreated. Lead poisoning is widespread and is not solely a problem of inner city or minority children. No socioeconomic group, geographic area, racial or ethnic population is spared.
New data indicate adverse effects of lead exposure in children at blood lead levels previously believed to be safe. Toxic effects have been documented at blood lead levels as low as 10 micrograms per deciliter (µg/dL) of whole blood. As a result, the Centers for Disease Control (CDC) 1985 intervention level of 25 µg/dL has been lowered to 10 µg/dL.
Because the erythrocyte protoporphyrin test is not sensitive enough to identify children with blood lead levels below 25 µg/dL, direct blood lead measurement is now the initial screening test. In addition, a multi-tier approach to follow-up has been adopted with an overall goal of reducing children´s blood lead levels below 10 µg/dL.
Attention: Effective immediately the North Carolina State Laboratory of Public Health will not process blood lead specimens collected on patients who are not residents of North Carolina. If a serious elevation was detected, North Carolina Environmental Health program would not have any jurisdiction in another state, causing follow-up issues.
Who and When to Screen
All children seen at local health departments for health maintenance visits (Well Child and Well Baby Clinics; Early Periodic Screening Diagnosis Treatment (EPSDT) Clinics; Pediatric Supervisory Clinics; WIC Children etc.) and all children receiving services through private providers are to be screened at least once before the age of six without regard to risk determination.
Ideally, children should be tested between 12 and 24 months of age, or upon their first entry to the health care system at a later age. Children identified as high risk should be rescreened in 12 months.
Screening specimen should be collected by the child´s primary care provider. Referral to a provider solely for the purpose of lead screening is discouraged.
Screening Test and Methodology
Direct blood lead measurement is the screening test of choice. Finger-stick, capillary blood specimens are adequate for the initial screening test, provided that precautions are taken to minimize the risk of contamination. Venous blood specimens should be collected for confirmation of all elevated blood lead results.
The State Laboratory is available to analyze blood specimens collected by local health departments and blood specimens on all children less than 6 years old seen by private providers.
Specimen Identification, Collection and Shipment
- DHHS form #3707 and specimen collection device kit are available from the Laboratory Mailroom (919-733-7656).
- Complete all information and identification on DHHS form #3707. It is imperative that all of the following information be given: last name, first name, middle initial, patient number (social security number), address, date of birth, race, sex, Medicaid number, submitter name, address and tax identification number (EIN#), specimen collection date, initial or follow-up blood lead test and microtainer or EDTA blood specimen (full, unopened tube).
- Prepare patient for collection
- Wash child´s hand with soap and water. Rinse well. Dry.
- Grasp the child´s hand so that the thumb of the blood drawer is across the top of the child´s fingers.
- Hold the child´s hand so that the palm faces up.
- Use child´s middle or ring finger for sample collection.
- Using an alcohol wipe, briskly scrub and are on the child´s fingertip for 20 seconds.
- Using dry gauze, wipe scrubbed area once.
- Use lancet to sick finger slightly left of center.
- Use dry gauze to wipe off the first drop of blood.
- After specimen collection, care of puncture site should be consistent with your institution´s procedures.
- Collection of Blood Sample
- Continuing to grasp the finger, touch the tip of the capillary of collection device to the beaded drop of blood.
- Capillary must be held continuously in a horizontal position during specimen collection to prevent air bubbles from forming in the capillary tube.
- After 3-4 drops of blood fall of the full capillary into the microtainer, you have enough blood (150-250ul).
- Turn capillary/tube unit immediately to a vertical position to allow the blood in the capillary into the tube.
- Remove capillary with holder at the same time. Close microtainer with attached cap.
- Agitate the specimen to mix the anticoagulant through the blood.
- Properly label with patient´s name and date of birth. Place in a refrigerator until shipping.
- The Laboratory must receive specimen within 2 weeks, however, immediate shipping is recommended to ensure specimen integrity and suitability for analysis.
Reporting and Follow-up Procedures
Children are classified according to the risk for adverse effects of lead based solely on blood lead measurement. The urgency and type of follow-up required are based on a child´s risk classification.
| Blood Lead Level | Follow-up Procedure |
|---|---|
| < 10 | Rescreen at 24 months of age. If follow-up result due to previously diagnosed level of 10 or greater: Retest every 2 - 3 months until three consecutive levels are below 10. |
| 10 - 19 | Conduct venous diagnostic test within 3 months. If diagnostic result: Retest every 2 - 3 months until 3 consecutive levels are below 10. If level persists at 10-19 for three months, refer for environmental investigation. |
| 20 - 44 | Conduct venous diagnostic test within 1 week. If diagnostic result: Refer for medical evaluation and environmental investigation. Retest every 2 - 3 months until three consecutive levels are below 10. |
| 45 + | Conduct venous diagnostic test AS SOON AS POSSIBLE. If diagnostic result: Refer for medical evaluation, chelation therapy, and environmental investigation. Retest every 2 - 3 months until three consecutive levels are below 10. |
