Dermal Puncture Medical Quiz

Dermal Puncture

• Also known as skin puncture or capillary puncture.
• Preferred method for blood collection in infants and children under 2 years old due to difficulty locating superficial veins, risks associated with deep vein puncture, prevention of iatrogenic anemia, specific test requirements (e.g., newborn screening), and potential injury from restraining.
• May also be necessary for adults with burns/scars, chemotherapy patients, obese individuals, apprehensive patients, those with thrombotic issues, geriatric patients with fragile veins, and those using home glucose monitoring or point-of-care testing (POCT).
• Not suitable for severely dehydrated patients, those with poor peripheral circulation, or swollen fingers. Certain tests (coagulation studies, ESR, blood cultures) require larger blood volumes than usually obtained via dermal puncture.

Importance of Correct Collection

• Specimen contamination must be avoided.
• Microclot formation is a concern.
• Hemolysis is more frequent.

Hemolysis Causes

• Excessive squeezing of the puncture site.
• Increased RBC count and fragility in newborns.
• Residual alcohol at the site.
• Vigorous mixing of microcollection tubes.

Capillary Blood Composition

• A mixture of capillary, arterial, and venous blood with small amounts of interstitial and intracellular fluid.

Dermal Puncture Equipment

• Automatic retractable safety skin puncture devices.
• Microcollection containers.
• 70% isopropyl alcohol pads, gauze pads, bandages.

Site Selection

• Avoid thumbs (calluses), index fingers (increased nerve endings), and fifth fingers (decreased tissue).
• Do not use swollen or previously punctured sites; these will contaminate the specimen due to increased tissue fluid.
• Earlobes are not recommended.

Warming the Site (Optional)

• Improves blood flow by dilating blood vessels and increasing arterial flow.
• Primarily for patients with cold/cyanotic fingers, multiple specimen heel punctures, and capillary blood gas (CBG) collection.
• Warm with a 42°C moist towel or commercial heel warmer for 3–5 minutes; do not exceed 10 minutes.

Cleaning the Site

• Use 70% isopropyl alcohol; allow to dry completely before collecting blood.
• Do not use povidone-iodine in routine extraction (except for blood cultures and blood donation); it can contaminate specimens and elevate bilirubin, phosphorus, uric acid, and potassium levels.

Performing the Puncture

• Ensure proper support and firm hold of the heel or finger without squeezing the puncture area.
• Apply gentle pressure before puncturing to increase blood flow.
• Proper heel puncture technique includes holding the heel with thumb and index finger around the arch, and surrounding fingers wrapping around the top of the foot.
• Dispose of puncture devices immediately after use in designated sharps containers. A new device is needed for additional punctures.

Specimen Collection

• Wipe away the first drop of blood to prevent contamination from alcohol and tissue fluid.
• Blood should flow freely; avoid "milking". Alternate pressure application yields better results.
• Avoid applying pressure very close to the puncture site; applying pressure further away may be better.
• Do not touch the puncture site with the lancet, as this leads to contamination and hemolysis.
• Position fingers downward to use gravity to fill capillaries. Do not use a scooping motion.

Capillary Tubes and Micropipettes

• Lightly touch the collection tip to the blood drop to draw it into the tube.
• Keep tubes horizontal during filling to prevent air bubbles (which interfere with blood gas determinations).
• Seal with sealant clay or designated caps. Apply sealant using twisting motion to firmly plug tubes.

Microcollection Tubes

• Hold at a slant, placing the tip beneath the drop. First 3 drops form a channel for blood flow. Gentle tapping may be needed.
• When full, add the color-coded top.
• Invert tubes with anticoagulants 5–10 times or as manufacturer directs.
• For slow blood flow, mix the tube during collection; collecting blood in more than 2 minutes may result in microclot formation.
• Collect the correct amount of blood; overfilling can lead to clotting while underfilling can alter cell morphology.

Order of Collection

• Order is important due to platelet accumulation.
• Use special kits with preprinted circles on filter paper; avoid touching the circles.
• Prevent contamination with water, formula, alcohol, urine, lotions, or powder.

Newborn Screening

• Typically collected 24-72 hours after birth via heel puncture by a medical technician, nurse, or physician.
• Use special kits; avoid contamination.

Newborn Screening Panel Diseases

• Congenital Hypothyroidism (CH): Lack of thyroid hormone.
• Congenital Adrenal Hyperplasia (CAH): Severe salt loss, dehydration, high male sex hormone levels.
• Galactosemia (GAL): Inability to process galactose.
• Phenylketonuria (PKU): Inability to properly use phenylalanine.
• Glucose-6-Phosphate Dehydrogenase Deficiency (G-6-PD def): Lack of G-6-PD enzyme. Most common.

Test your knowledge on dermal puncture techniques and their significance in blood collection, particularly for infants and patients with special conditions. Learn about the advantages, contraindications, and best practices to ensure accurate specimen collection. This quiz provides essential information for healthcare professionals.