Why is the order of draw different for a capillary puncture from a venipuncture collection

This “Phlebotomy Webinar” will review the physiologic differences between capillary and venous blood, and discuss advantages and limitations to each specimen type. Also covered will be specific use cases and advantages to using capillary sampling for infants and children, as well as circumstances and specific tests where capillary blood provides advantages over venous blood in adult patients.

Presenter

Learning Objectives

Upon completion of this activity, participants should be able to:

• Review physiologic differences between capillary and venous blood.
• List situations where capillary blood is an appropriate sample type for infants and children.
• Describe limitations to the use of capillary blood samples in infants and children.
• Define unique situations and tests where capillary blood may be the preferred sample type for adult patients.

Intended Audience

This series is appropriate for phlebotomists, phlebotomy managers, phlebotomy educators, and other patient-care staff involved in specimen collection.

Faculty Disclosure

Course director(s), planning committee, faculty, and all others who are in a position to control the content of this educational activity are required to disclose all relevant financial relationships with any commercial interest related to the subject matter of the educational activity. Safeguards against commercial bias have been put in place. Faculty members also will disclose any off-label and/or investigational use of pharmaceuticals or instruments discussed in their presentations. Disclosure of this information will be published in course materials so those participants in the activity may formulate their own judgments regarding the presentations.

In order to collect blood with a capillary tube, the appropriate site must be cleaned and punctured with a lancet so that a drop of blood can be gently expressed.

But what is an appropriate site?

• Finger - Usually the third or fourth finger is preferred in adults and children. The thumb has a pulse and is likely to bleed excessively. The index finger can be calloused or sensitive and the little finger does not have enough tissue to prevent hitting the bone with the lancet. The puncture is done to the left or right of the midline of the palmar surface of the fingertip, staying away from the fingernail.
  
  

• Heel - This site is used for infants, less than one year old, whose fingers are too tiny. The puncture is done on the farthest lateral or medial aspect of the plantar surface of the heel, not on the bottom. Punctures done on the plantar surface can damage cartilage or bone.
  
  
  

• Ear lobe - The ear lobe has been used for capillary blood sampling, but is no longer recommended. Studies have shown that the blood flow in the ear lobe is less than that in either the finger tip or the heel. The ear lobe can still be used if no other site is available.

  Blood samples must be drawn by phlebotomists in a specific order to avoid cross-contamination of the sample by additives found in different collection tubes. Phlebotomy order of draw is the same for specimens collected by syringe, tube holder, or into tubes preevacuated at the time of collection. The correct order of draw follows:

  1. Blood culture tube or bottle
  2. Sodium citrate tube (eg, blue closure)
  3. Serum tubes, including those with clot activator and gels (eg, red, red-speckled, gold closures)
  4. Heparin tube with or without gel (eg, dark green, light green, speckled green closures)
  5. EDTA tube with or without gel separator (eg, lavender, pearl, pink closures)
  6. Sodium fluoride/potassium oxalate glycolytic inhibitor (eg, gray closure)

  The placement of tubes not listed here should take into consideration the potential for their additive to alter results obtained from the next tube if carryover were to occur. Plastic serum tubes containing a clot activator may cause interference in coagulation testing. Only blood culture tubes, glass nonadditive serum tubes, or plastic serum tubes without a clot activator may be collected before the coagulation tube.

  Numerous errors can occur during the collection and handling of blood specimens, which pose significant and avoidable risks to the patient and the phlebotomist. When global standards are not fully implemented, it is more likely that patients will be injured during the procedure, biologically representative specimens will not be obtained from patients, and test results will not be comparable from one facility to another.

  CLSI’s GP41 —Collection of Diagnostic Venous Blood Specimens provides a descriptive, stepwise process and procedures reflecting the quality system essentials format for diagnostic venous blood specimen collection. Special considerations for collections from vascular access devices, blood culture collection, and collections in isolation environments are included, as well as how to handle emergency situations. An expanded appendix section provides helpful tips for collecting specimens from pediatric and other challenging patients.

  Is the order of the draw the same for capillary draws as it is for venipuncture specimens?

  Order of draw. With skin punctures, the haematology specimen is collected first, followed by the chemistry and blood bank specimens. This order of drawing is essential to minimize the effects of platelet clumping. The order used for skin punctures is the reverse of that used for venepuncture collection.

  What is the difference between venipuncture and capillary puncture?

  Capillary blood sampling is becoming a common way to minimize the amount of blood drawn from a patient. The 10 or 20 microliters can be used to look for anemia, check blood sugar or even to evaluate thyroid function. The procedure is easier and less painful than traditional venipuncture which draws blood from a vein.

  When performing capillary draws what is the order of draw?

  The order of draw is based on CLSI Procedures and Devices for the Collection of Capillary Blood Specimens; Approved Standard - Sixth Edition, September 2008. This standard recommends that EDTA tubes be drawn first to ensure good quality specimen, followed by other additive tubes and finally, serum specimen tubes.

  In which of the following areas does capillary specimen collection differ from routine venipuncture for tests that can be collected either way?

  Phlebotomy final test.