Capillary Puncture

Which of the following is a recommended site for finger puncture in adults?

• End segment of the little finger

• Distal segment of the middle finger

• Plantar surface of the index finger

• Proximal segment of the ring finger

Answer explanation

 When selecting a dermal puncture device, the

most critical consideration is the:

•  width of the incision

•  amount of blood needed

•  depth of the incision

•  tests requested

Answer explanation

  To prevent contact with bone, the depth of

the puncture is critical. The Clinical and Laboratory

Standards Institute (CLSI) recommends that the incision

depth should not exceed 2.0 mm in a device used to perform heelsticks. There is concern that even

this may be too deep in certain infants, particularly

premature infants.

 The concentration of this analyte is higher in

blood collected by dermal puncture than in

venipuncture:

•  glucose

•  potassium

•  total protein

•  calcium

Answer explanation

 Capillary blood is a mixture of arterial and venous

blood and may contain small amounts of interstitial

and intracellular fluids. Potassium, total

protein, and calcium have lower concentrations

in capillary blood and glucose is higher. Note on

the requistion when capillary blood is collected.

 A test included in a newborn screen that is

collected using filter paper is:

•  PKU

•  electrolytes

•  bilirubin

•  CBC

Answer explanation

Newborn screening program in the Philippines currently includes screening of six disorders: Congenital Hypothyroidism (CH), Congenital Adrenal Hyperplasia (CAH), Phenylketonuria (PKU), Galactosemia (GAL), Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency and Maple Syrup Urine Disease (MSUD).

 Failure to puncture across the fingerprint will

cause:

•  blood to run down the finger

•  hemolysis

•  contamination of the sample

•  additional patient discomfort

Answer explanation

 The blade of the puncture device should be aligned to cut across (perpendicular to)

the grooves of the fingerprint or heel print. This aids in the formation of a rounded drop because the

blood will not have a tendency to run into the

grooves.

 The maximum length of a puncture device used

on the heel is:

•  1.0 mm

•  1.5 mm

•  2.0 mm

•  2.5 mm

Answer explanation

 A variety of automated retractable puncture devices

are available. The type of device selected depends

on the age of the patient, the amount of blood sample required, the collection site, and the puncture depth. The incision depth should

not exceed 2.0 mm in a device used to perform

heelsticks.

Capillary puncture supplies include all of the

following except:

• Gauze pad

• Lancet

• Microcollection device

• Povidone–iodine pad

Answer explanation

Do not use povidone–iodine to clean skin puncture sites because it greatly interferes with a number of tests, most notably bilirubin, uric acid, phosphorus, and potassium.

Which of the following is the least hazardous

area of an infant’s foot for capillary puncture?

• Central area of the heel

• Lateral plantar heel surface

• Medial area of the arch

• Posterior curvature of the heel

Answer explanation

According to CLSI, to avoid puncturing bone the only safe areas for heel puncture are on the plantar surface of the heel, medial to an imaginary line extending from the middle of the

great toe to the heel or lateral to an imaginary line extending from between the fourth and fifth toes to the heel

Which of the following conditions disqualifies a

site for capillary puncture?

• Cyanotic

• Edematous

• Swollen

• All of the choices

Answer explanation

General site selection criteria include one that is warm, pink or normal color, and free of scars, cuts, bruises, or rashes. It should not be cyanotic (bluish in color), edematous (swollen), or infected. Swollen or previously punctured sites should be avoided, because accumulated tissue

fl uid can contaminate the specimen and negatively affect test results.

If using capillary puncture to collect the following microtubes from a patient, which one would be collected fi rst?

• Gray top

• Green top

• Purple top

• Red top

Answer explanation

 The order of draw for collecting multiple samples from

a dermal puncture is important because of the tendency

of platelets to accumulate at the site of a wound. Blood

to be used for tests for the evaluation of platelets, such

as the blood smear, platelet count, and complete blood

count (CBC), must be collected first. The blood smear should be made first, followed by the lavender EDTA

tube. The order of collection for multiple tubes is