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Preventing Lead Poisoning in Young Children: Appendix I.

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Appendix I. Capillary Sampling Protocol

Microspecimens of blood collected by fingerstick are widely used to measure lead levels, yet there is no consensus on what constitutes the best collection procedure. Published data on collection methods are scant, and much of the data that do exist were published 10 or more years ago, when technology was not as advanced and blood lead levels of concern were significantly higher.

The high potential for lead contamination of capillary specimens during collection is well known (CDC, 1985; DeSilva and Donnan, 1980; Mitchell et al., 1974), and the special steps used to minimize the likelihood of contamination constitute the major differences among collection procedures. Special procedures used for minimizing contamination include thorough scrubbing of the hand and finger with soap and then alcohol (Sinclair and Dohnt, 1984; NECCLPP, 1985); using dilute nitric acid (Rosen, 1972; MHD, 1988); or using silicone or a similar barrier spray (Lyngbye et al., 1990; CDHS, 1990; NYSDH, 1989; Mitchell et al., 1974).

Several types of containers for collecting children's blood (maximum volume < or = to 500 µL) have been introduced in recent years and are widely used by screening programs. The new containers are better than glass tubes, since glass capillary tubes are very fragile. Whether these new containers are suitable for collecting blood for lead measurement has not been extensively studied.

More research on these and other issues is clearly needed before the best fingerstick collection procedures can be identified. Recognizing these constraints, a fingerstick procedure for collecting blood lead specimens follows.

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A. Needed Materials

  1. Soap.
  2. Alcohol swabs. If a surgical or other disinfectant soap is used, alcohol swabs can be eliminated.
  3. Sterile cotton balls or gauze pads.
  4. Silicone spray or swabs. The benefits of using a barrier spray, which forms a layer between the skin and blood droplets, have been debated. In addition to doubts about the spray's effectiveness in reducing specimen contamination, the spray makes the collection more expensive and complex. Some evidence exists, however, the spray reduces contamination (NYSDH, 1989; Mitchell et al., 1974), so it is included in this procedure.
  5. Examination gloves.
  6. Lancets. The type of lancet used is largely a matter of personal preference, so long as sterility is guaranteed.
  7. Collection containers. If glass capillary tubes are used, sealing clay or tube caps will also be required. No additional supplied are needed for most other microcontainers. The laboratory should be consulted to ensure than an appropriate size capillary tube is used.
  8. Adhesive bandages.
  9. Trash bags suitable for medical waste and containers for sharps. Bags containing medical waste should be clearly identified as such.
  10. Storage or mailing containers if needed. If specimens require shipment, follow the Postal Service or other appropriate regulations for shipping body fluids.

Materials used in the collection procedure that could contaminate the specimen (for example, blood containers, alcohol swabs, and barrier sprays) must be lead-free. Before selecting equipment for use in blood collection, consult with the laboratory about its requirements. In many cases, the laboratory will recommend or supply suitable collection equipment and may precheck the equipment for lead contamination. Some instrument manufacturers also supply collection materials that are pretested for lead content.


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B. Preparing for Blood Collection

All personnel who collect specimens should be well-trained in and thoroughly familiar with the collection procedure. The skill of the collector will greatly influence the specimen quality. All equipment should be within easy reach. The environment should be clean, secure, and as nonthreatening to the child as possible. Any necessary consent should be obtained before specimen collection begins, and the procedure should be explained to the child and the parent or guardian. Used materials should be discarded into appropriate waste containers suitable for medical waste immediately following use.

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C. Preparing the Finger for Puncture

NOTE: Puncturing of the fingers of infants less than 1 year of age is not recommended. Puncturing of the heel is more suitable for these children (NCCLS, 1986).

Collection personnel should wear examination gloves whenever the potential for contact with blood exists. If the gloves are coated with powder, it should be rinsed off with tap water.

The child's hands should be thoroughly washed with soap and then dried with a clean, low lint towel. If water is unavailable, foam soaps can be used without water (D. Griffin, Louisville/Jefferson County Department of Health, personal communication). Plain, unprinted, nonrecycled towels are best (WSLH, 1985). If desired, a brush can be used for cleaning the finger; brushing during washing can increase blood circulation in the finger (CDHS, 1990). Once washed, the finger must not be allowed to come into contact with any surface, including the child's other fingers.

The finger to be punctured (often the middle finger) must be free of any visible infection or wound; it should be massaged to increase circulation before being punctured with the lancet. This can be accomplished during or after washing (NYSDH, 1989; CDHS, 1990).

Steps for Preparing the Child's Finger

  1. Select examination gloves. If necessary, rinse them to remove powder.
  2. Wash the child's hands thoroughly with soap and water, and then dry them with an appropriate towel.
  3. Grasp the finger that has been selected for puncture between your thumb and index finger with the palm of the child's hand facing up.
  4. If not done during washing (see preceding notes), massage the fleshy portion of the finger gently.
  5. Clean the ball or pad of the finger to be punctured with the alcohol swab. Dry the fingertip using the sterile gauze or cotton ball.
  6. Apply the silicone barrier. If a spray is used, shake the can vigorously to mix the contents. Direct the spray away from child and collector. Silicone does not dry, and the finger can be punctured immediately.

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D. Puncturing of the Finger and Forming Drops of Blood

  1. Grasp the finger and quickly puncture it with a sterile lancet in a position slightly lateral of the center of the fingertip.
  2. Wipe off the first droplet of blood with the sterile gauze or cotton ball.
  3. If blood flow is inadequate, gently message the proximal portion of the finger and then press firmly on the distal joint of the finger. A well-beaded drop of blood should form at the puncture site.
  4. Do not let the blood run down the finger or onto the fingernail.

After the finger is ready, the puncture and subsequent steps of forming a drop of blood and filling the collection container should be performed quickly and efficiently, since any delay can make collection more difficult (for example, the blood may clot or the child may resist). Several types of lancets are suitable for puncturing children's fingers. The range from small manual lancet blades to spring-loaded assemblies. Regardless of the lancet used, the puncture should be made swiftly and cleanly and should be deep enough to allow adequate flow.

The site of the puncture should be slightly lateral to the ball of the finger. This region is generally less calloused, which makes puncturing easier and, possibly less painful (CDHS, 1990). The first drop of blood contains tissue fluids that will produce inaccurate results; it should be removed with a sterile gauze or cotton ball (NYSDH, 1989; CDHS, 1990).

A barrier material such as silicone will help a distinct "bead" of blood to form, which aids collection. Blood that runs down the finger or around the fingernail is no longer suitable. Blood flows better if the punctured finger is kept lower than the heart. Inadequate blood flow can be improved by gently massaging the proximal portion of the finger in a distal direction, then pressing firmly at the distal joint of the punctured finger (restricting blood flow out of the fingertip) and gently squeezing the sides of the fingertip. Excessive squeezing will cause tissue fluid to be expressed, and the fluid will compromise specimen integrity (NYSDH, 1989; CDHS, 1990). Do not let the blood run down the finger or fingernail.

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E. Filling the Collection Container

  1. Continuing to grasp the finger, touch the tip of the collection container to the beaded drop of blood.
  2. Draw the blood into the container maintaining continuous flow of blood.
  3. When full, cap or seal the container as appropriate.
  4. Agitate the specimen to mix the anticoagulant through the blood.
  5. Check that the container is properly labeled, and place it in an appropriate storage area.
  6. Stop the bleeding and cover the finger with an adhesive bandage. Bleeding should stop very quickly. If bleeding is slow to stop, apply pressure to the puncture site with a sterile gauze or a cotton ball. If bleeding continues after 3 to 5 minutes of applying pressure, consult a physician.

The proper procedure for filling and capping collection containers is somewhat specific to the container used. As a general rule, contact between the skin and the container is to be avoided. To prevent clotting of the specimen, blood must be mixed with the anticoagulant after filling the container. Depending on the container and anticoagulant used, the agitation needed can range from gentle rocking to vigorous shaking. Some procedures call for the collection container to be rotated during filling so that anticoagulant will be distributed quickly through the sample (MDPH, 1990).

To facilitate blood flow, many procedures call for the collection container be held nearly horizontal, with a slight downward angle. Blood flow into the container should be uninterrupted to avoid air bubbles in the specimen. Except for glass capillary tubes, containers come with appropriate caps, and these should be applied immediately following collection. Specimens in glass capillary tubes are often collected in duplicate and then sealed with rubber caps or plasticine sealing clay or both. Again, consulting with the laboratory and knowing the manufacturer's recommendations are important to ensure specimen integrity and suitability for analysis.

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CDHS (California Department of Health Services). Childhood blood lead screening: finger stick blood sampling method. Berkeley (CA): CDHS, 1990.

CDC (Centers for Disease Control). Preventing lead poisoning in young children: a statement by the Centers for Disease Control. Atlanta: CDC. 1985; CDC report no. 99-2230.

De Silva PE, Donnan MB. Blood lead levels in Victorian Children. Med J Aust 1980;1:93.

Lyngbye T, Jorgensen PJ, Grandjean P, Hansen ON. Validity and interpretation of blood lead levels: a study of Danish school children. Scand J Clin Lab Invest 1990;50:441-9.

MDPH (Massachusetts Department of Public Health). Procedure for obtaining finger stick blood samples. Jamaica Plain (MA): MDPH, Childhood Lead Poisoning Program, 1990.

MHD (Milwaukee Health Department). Generalized procedure finger stick blood (hematocrit and/or lead test). Milwaukee: MHD, 1988.

Mitchell DG, Aldous KM, Ryan FJ. Mass screening for lead poisoning: capillary blood sampling and automated Delves-cup atomic-absorption analysis. N Y State J Med 1974;74:1599-603.

NCCLS (National Committee for Clinical Laboratory Standards). Procedures for the collection of diagnostic blood specimens by skin puncture- second edition. NCCLS publication H4-A2. Villanova (PA): NCCLS, 1986.

NECCLP (New England Consortium of Childhood Lead Poisoning Programs). New England public health laboratory lead testing services [report]. Providence (RI): NECCLPP, 1985.

NYSDH (New York State Department of Health). Blood lead and Erythrocyte Protoporphyrin: a recommended procedure for collecting finger stick blood specimens. Albany (NY): NYSDH, Wadsworth Center for Laboratories and Research. 1989.

Rosen JF. The microdetermination of blood lead in children by flameless atomic absorption: the carbon rod atomizer. J Lab Clin Med 1972;80: 567-76.

Sinclair DF, Dohnt BR. Sampling and analysis techniques used in a blood lead survey of 1241 children in Port Pirie, South Australia. Clin Chem 1984;10:1616-9.

WSLH (Wisconsin State Laboratory of Hygiene). Complete sampling instructions for capillary lead. Madison (WI): WSLH, University of Wisconsin Center for Health Sciences, 1985.

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