Venous, Arterial, and Capillary Blood Specimens
Venous Blood
Venous blood is deoxygenated blood that flows from tiny capillary blood vessels within the tissues into progressively larger veins to the right side of the heart.
Venous blood is the specimen of choice for most routine laboratory tests. The blood is obtained by direct puncture to a vein, most often located in the antecubital area of the arm or the back (top) of the hand. At times, venous blood may be obtained using a vascular access device (VAD) such as a central venous pressure line or Hickmann Catheter or an IV start. Most laboratory reference ranges for blood analytes are based on venous blood.
Arterial Blood
Deoxygenated blood is pumped from the right side of the heart to the lungs where it takes up oxygen. The now oxygenated blood is pumped through the left side of the heart via arteries.
The most common reason for collection of arterial blood is the evaluation of arterial blood gases. Arterial blood may be obtained directly from the artery (most commonly, the radial artery) by personnel who are trained to perform this procedure and are knowledgeable about the complications that could occur as a result of this procedure. Arterial blood may also be obtained from a vascular access device (VAD) inserted in an artery such as a femoral arterial line or Swan-Gantz catheter.
Capillary Blood
Capillary blood is obtained from capillary beds that consist of the smallest veins (venules) and arteries (arterioles) of the circulatory system. The venules and arterioles join together in capillary beds forming a mixture of venous and arterial blood. The specimen from a dermal puncture will therefore be a mixture of arterial and venous blood along with interstitial and intracellular fluids.
Capillary blood is often the specimen of choice for infants, very young children, elderly patients with fragile veins, and severely burned patients. Point-of-care testing is often performed using a capillary blood specimen.
Specimen Type
Method of Collection
Common Use
Venous Direct puncture of vein by venipuncture; vascular access device
Routine laboratory tests
Arterial Direct puncture of artery; vascular access device
Arterial blood gases
Capillary Dermal puncture of fingertip or heel
Infants and young children
Elderly patients with fragile veins
Severly burned patients
Point-of-care testing
Lab Dept:
Chemistry
Test Name:
CAPILLARY BLOOD GAS (CBG)
General Information
Lab Order Codes:
CBG
Synonyms:
CBG
CPT Codes:
82803 – Gases, blood, any combination of pH, pCO2,pO2, CO2, HCO3 (including calculated O2 saturation)
Test Includes:
pH (no units), pCO2 measured in mmHg, HCO3 and BE measured in mmol/L, Temperature (°C) and ST (specimen type)
Logistics
Test Indications:
Capillary blood gas determinations are useful in monitoring neonates or other patients when arterial collection is not practical. Arteriolization of the capillary bed yields pH and pCO2 comparabe to arterial blood. Useful for evaluating oxygen and carbon dioxide gas exchange; respiratory function, including hypoxia; and acid/base balance. It is also useful in assessment of asthma; chronic obstructive pulmonary disease and other types of lung disease; embolism.
Lab Testing Sections:
Chemistry
Phone Numbers:
MIN Lab: 612-813-6280
STP Lab: 651-220-6550
Test Availability:
Daily, 24 hours
Turnaround Time:
30 minutes
Special Instructions:
See Collection and Patient Preparation
Specimen
Specimen Type:
Whole blood
Container:
Lithium Heparinized Capillary blood gas tube tightly capped with internal mixing flea.
Draw Volume:
MIN campus: 0.14 mL (Minimum: 0.07 mL) blood STP campus: 0.2 mL (Minimum: 0.1 mL) blood
Note: Submission of 0.1 mL of blood in one capillary tube does not allow for repeat analysis.
Processed Volume:
0.1 mL blood per analysis
Collection:
Perform a capillary puncture from an arteriolized site. Fill 2 capillary tubes completely without introducing air bubbles. Cap both ends and mix 20 times by gentle inversion. Forward immediately at ambient temperature only. Do not expose the specimen to air.
Do not mix capillary samples from neonates with a magnet. Use gentle and thorough inversion only.
Special Processing:
Lab Staff: Deliver the specimen to the blood gas testing station. Testing should be completed within 15 minutes of collection.
Patient Preparation:
The skin area to be punctured should be warmed to no more than 42°C for 3-10 minutes by applying an infant heel warmer. The patient should be in a relaxed and steady state
Sample Rejection:
Clotted specimen; unlabeled specimen or mislabeled specimens; specimens >30 minutes old; specimen contaminated with large air bubbles
Interpretive
Reference Range:
pH:
7.35 – 7.45
PCO2:
Males:
35 – 48 mm Hg
Females:
32 – 45 mm Hg
HCO3:
22 – 27 mEq/L
Base Excess:
Newborn (0 – 7 days):
-10 to -2 mmol/L
Infant (1 week – 1 year):
-7 to –1 mmol/L
Child (1 – 16 years):
-4 to +2 mmol/L
Adult (>16 years):
-3 to +3 mmol/L
Critical Values:
pCO2: <15 or >70 mm Hg
pH: <7.2 or >7.6
Limitations:
N/A
Methodology:
Ion-Selective Electrode, HCO3 and BE by calculation
References:
Tietz, Norbert (1995) Clinical Guide to Laboratory Tests, 3rd edition, WB Saunders Co, pp 1081-1084
ABL 800 FLEX Operator’s Manual, Publication 201410, Edition E, Code Number 994-909, 2008 Radiometer Medical ApS
Jacobs and DeMott (2001) Laboratory Test Handbook, 5th edition, Lexi-Comp, Inc., Hudson, Ohio, p 21
ABL90 FLEX Operator’s Manual, Publication 201403, Edition H, Code 996-656
Update:
7/14/2005: Added clarification on draw volume for repeat analysis. 4/22/2010: TAT update, previously listed as 1 hour, updated references
