Micro Blood Collection

Pediatric specimens may be submitted in low-volume collection tubes or may be collected by finger-stick. Infant specimens are best collected using a heel-stick.

Main Line Health Laboratories (MLHL) provides the following standard procedures for micro blood collection.

Finger-Stick Collection

Site Selection

Finger-sticks should be performed on the palmer surface of the distal phalanx of the index, ring or middle finger. Middle or ring fingers are most desirable, since the index finger has an increased number of nerve endings and is therefore more sensitive. The sides and the tips of the distal phalanx should not be used, as the tissue on this area of the finger is only half as thick as that on the palmer surface. The fifth finger is not used for skin puncture, as the tissue on this finger is considerably thinner than that on other fingers. Finger-sticks should be performed perpendicular to the fingerprints. If the puncture is made parallel to the fingerprints, the blood will channel down the patient's finger instead of forming a drop at the puncture site, making the collection much more difficult.

Preparing the Finger

1. Choose a finger that is not cold, cyanotic (blue) or swollen. Many times, the puncture site will require warming to facilitate blood collection. The simplest method of warming the site is to cover it for three minutes with a warm, moist towel or a commercial skin-warming gel pack. Temperature must not exceed 40° C, the optimal warming temperature.
2. With your left thumb and index finger, grasp either the patient's long or ring finger about three inches above the tip of the finger.
3. With your right hand, hold the sides of the patient's finger.
4. Moving your left hand toward the tip of the patient's finger, apply a massaging motion to the fleshy portion of the finger.
5. Repeat this massaging process five or six times.
6. Cleanse the puncture site using a 70 percent alcohol pad.
7. Allow the site to air-dry to provide disinfecting and to prevent possible hemolysis by residual alcohol.

Performing the Puncture

1. 

   Hold the finger with a moderately firm grip. Place your hand against a support, if possible, to prevent movement.
2. Place the sterile lancet against the site, holding it between your thumb and middle finger. Position the lancet to cut transversely to the axis of the finger.
3. Depress the plunger using your index finger and hold for a split second.
4. Release the plunger.
5. Remove the lancet.
6. Discard the lancet into a sharps container.

Collecting the Specimen

1. Wipe away the first drop of blood with a gauze pad as this drop may contain an excess of tissue fluids, which could cause erroneous test results.
2. Turn the patient's hand palm down.
3. Microtainer® (Bullet) collection:
   • Position the Microtainer (Bullet) directly beneath the puncture site. Intermittent gentle application and relaxation of pressure on the entire finger allows the capillaries to refill with blood and helps assure continuous blood flow. Apply pressure at the ends of the puncture slit, opening the puncture slightly. This will maximize blood flow.
   • Since the puncture site needs to remain free of residual blood, wipe it frequently with a gauze pad. Milking or scraping the puncture site should be avoided, since it can cause hemolysis or contamination of the specimen.
   • During difficult or slow collections using EDTA (Lavender) tubes, try to rotate the collector after each of several drops. This will hasten the contact of the blood with EDTA while collecting.
   • Tubes should be filled quickly to a level between the lines. Work quickly to minimize the chance of microclots forming in the EDTA tube.
   • When each collection is complete, securely cap and mix additive tubes thoroughly by inversion at least 20 times. This is especially important for EDTA tubes.
   • Send any partially filled tubes to the laboratory to determine if they are suitable for testing.
   • If it is necessary to collect more blood from an additional puncture, begin again by warming the site, cleansing, drying, resticking with a new lancet and collecting into an unused tube.

Completing the Procedure

1. Wipe the site dry and apply direct pressure with a gauze pad until the bleeding has stopped.
2. Dispose of all used materials in an appropriate biohazard container.
3. Label the tubes with complete patient name as it appears on the test requisition form, the date and time of specimen collection and collectors tech code or initials, and transport them to the lab for processing. Samples collected in EDTA for hematology must be tested within four hours of collection.

Heel-Stick Collection

Collection of blood specimens by heel-stick is used in infants and very young children when venipuncture is not the method of choice. Blood obtained by skin puncture consists of a mixture of blood from arterioles, venules and capillaries. Blood collected by skin puncture is also affected by interstitial and intracellular fluid. It is important to note the method of collection (i.e., heel-stick) on the request slip.

Site Selection

The recommended site of a heel-stick is on the plantar surface, either medial to a line drawn posteriorly from the great toe to the heel, or lateral to a line drawn posteriorly from between the fourth and fifth toes to the heel. Do not puncture at the posterior curvature. Be sure the site is not edematous so tissue fluid will not contaminate the specimens.

Note: Do not puncture through a previous site because of the danger of infection.

Preparing the Heel

1. Many times, the puncture site will require warming to facilitate blood collection. The simplest method of warming the site is to cover it for three minutes with a warm, moist towel or commercial warming device.
2. Prep the skin by cleansing with a 70 percent alcohol prep and allow to dry.

Performing the Puncture

1. Immobilize the foot by placing your fingers around the arch, behind the heel and well below the puncture site, as illustrated.
2. When using a Microtainer or Tenderfoot® lancet, place the lancet perpendicular to the heel print.
3. Hold the lancet on site with moderate pressure.
4. Depress the plunger with the index finger to make a puncture.
5. Immediately release the plunger while holding the lancet on site.
6. Remove the lancet.
7. Discard the lancet in a sharps container.
8. Wipe away the first drop of blood with a gauze pad, as this drop may contain an excess of tissue fluid, which can cause erroneous test results.

Collecting the Specimen

1. Collect the blood, using a Microtainer® or capillary tube. Moderate pressure, without squeezing, may be required near the puncture site to assure an adequate flow of blood.
2. When performing a heel-stick, apply pressure only to the foot. Do not "milk" the infant's leg. Since the puncture site needs to remain free of residual blood, wipe it frequently with a gauze pad. Milking or scraping the puncture site should be avoided since it can cause hemolysis or contamination of the specimen. During difficult or slow collections using EDTA (Lavender) tubes, try to rotate the collector after each several drops. This will hasten the contact of the blood with EDTA while collecting.
3. Tubes should be filled quickly to a level between the lines. Work quickly to minimize the chance of micro-clots forming in the tube.
4. When each collection is complete, securely cap and mix additive tubes thoroughly by inversion at least 20 times. This is especially important for EDTA tubes.
5. Order of collection: EDTA tubes, other additive tubes (Green or Gel), Red top tubes.

Completing the Procedure

1. Following collection of blood sample, press a sterile sponge to the puncture site until bleeding stops. Elevating the foot above the level of the heart will help stop bleeding.
2. Apply a "Spot Band-Aid" to the site once the bleeding has stopped.
3. Dispose of all used materials in an appropriate biohazard container.
4. Label the tubes with complete patient name as it appears on the test requisition form, the date and time of specimen collection and the collector's tech code or initials, and transport them to the lab for processing.

References:
Becton Dickinson. "Microcollection: A Quick Reference Guide." 1991.
College of American Pathologists. "So You're Going to Collect a Blood Specimen." 1982.
Susan Phelan. "Phlebotomy Techniques: A Laboratory Workbook." ASCP Press, 1993.

Note: Coagulation testing and certain esoteric testing cannot be collected by micro-collection techniques. Refer to the submission requirements in the Directory of Services.