Blood Specimen Collection
Blood Specimen Collection
Blood specimen collection is performed routinely to obtain blood for laboratory testing. Blood can be obtained from venous access devices and sometimes by fingerstick. Blood is most frequently obtained via a peripheral vein puncture (venipuncture).
Blood is usually drawn and collected in order to perform a variety of laboratory tests. Specimens are often sent to help diagnose conditions such as electrolyte imbalances, to screen for risk factors like high cholesterol levels, and to monitor the effects of treatments and medications.
Although obtaining blood specimens is a routine function, it is one of the riskiest procedures nurses perform. To increase the safety of blood collection, these precautions should be followed:
- Avoid using syringes. Use vacuum tube blood-collection devices instead, preferably those with needle-stick prevention features.
- Do not use a needle when withdrawing blood from a peripheral intravenous line or from a central venous access device. Using a needleless system allows the blood to be drawn directly into specimen containers.
- Do not use an exposed needle to inject blood into specimen containers or vacuum tubes.
When drawing blood, the health care professional should follow universal precautions as set forth by the Centers for Disease Control and Prevention (CDC). Universal precautions help reduce the risk of exposure of the health care professional's skin and/or mucus membranes to infectious materials. It includes the use of a variety of protective barriers, such as gloves, masks, gowns, and eyewear. Good hand washing practices before and after drawing blood also reduce the exposure risk.
These precautions were designed to prevent the transmission of hepatitis B virus (HBV), human immunodeficiency virus (HIV), and other bloodborne pathogens. Universal precautions apply to blood, semen, vaginal secretions, and any other body fluids containing blood. They also apply to tissues, as well as pleural, cerebrospinal, synovial, peritoneal, pericardial, and amniotic fluids. Universal precautions do not apply to stool, nasal secretions, sputum, sweat, tears, urine, saliva, and vomit unless these visibly contain blood.
Prior to obtaining blood specimens, the nurse should assess the patient, noting factors that may affect test results, including medications, pregnancy, age, and sex. Make sure the patient has followed any special instructions, which could include fasting for a number of hours or taking a medication at a certain time.
Patients should also be assessed for their knowledge level regarding the tests ordered. Instruct the patient as needed about the test and the procedure itself. Although most blood work does not require any special consent, some tests, like those for HIV, usually do. If needed, obtain consent prior to collecting the specimen.
There are four patient "rights" the nurse should consider when collecting blood specimens. These rights are:
- Right specimen. Make sure the specimen collected is the specimen ordered.
- Right time. Certain blood tests must be obtained at specific times. For example, when drawing antibiotic levels, trough specimens should be obtained immediately prior to the next dose. The time to draw peak levels may be dependent upon whether the antibiotic is given intravenously, orally, or intramuscularly.
- Right patient. Always verify the patient's identification before drawing a blood specimen. The person drawing the specimen should also label the container it is drawn into.
- Right method. Always follow universal precautions when performing a venipuncture.
Before puncturing, the patient's skin should be cleaned. Povidone-iodine (Betadine) can be used, or alcohol, unless an ETOH level is being drawn (alcohol on the skin may elevate an ETOH result). Povidone-iodine should always be used if blood cultures are to be drawn.
Techniques to find a vein include lowering the arm into a dependent position to help dilate the veins; applying warm soaks on the arm to improve venous dilation; and having the patient open and close the fist after applying a tourniquet. The health care provider can also attempt to palpate a vein where it is expected to be, since veins can often be felt, yet not seen. Arteries pulsate and have a thick wall. Thrombosed veins feel cord-like, and roll easily.
There are three veins in the antecubital (the inner or front surface of the forearm) area that are appropriate for venipuncture: the medial, cephalic, and basilic veins. The vein of choice is the medial, because it is usually the closest to the skin's surface, the largest, and usually the least painful to puncture. If the antecubital sites cannot be accessed, wrist and hand veins are also acceptable for venipuncture.
Venipuncture is usually done using a vacuum container (Vacutainer) system. This system consists of vacuumized specimen tubes, a needle, and a plastic holder. When the tube is placed into the holder and pressed against the needle, negative pressure results, and blood is pulled into the tube. Normally, a 21-gauge needle is used to collect blood. Occasionally, depending on the test ordered and specific patient circumstances, a larger or smaller diameter needle may be appropriate. Never insert the needle at greater than a 30 degree angle. Doing so increases the possibility of passing through the vein and into those structures lying underneath, raising the chances of permanent injury to the patient.
A number of other guidelines should be considered when performing venipunctures for blood specimen collection. These include:
- Avoid drawing blood from an arm affected by a stroke or neurological injury that has resulted in a loss of sensation. The patient may not be able to alert you if they experience pain or other problems.
- Avoid drawing blood from the arm on the affected side if a woman has had a mastectomy (full or partial breast tissue removal).
- Avoid areas with extensive scarring. Scar tissue is difficult to puncture.
- Attempt to collect the blood specimen from the opposite arm if a patient is receiving intravenous fluids, since fluid may dilute the blood sample.
- Do not use a site that is swollen, affected by certain skin conditions like eczema, or is infected.
- Use the right specimen tubes. Using the wrong tubes will cause the specimen to be rejected by the laboratory.
- Try using pediatric tubes when a patient has fragile veins that may not provide a large enough specimen. Though the smaller tubes store less blood, they will still give reliable results.
- Remove the tourniquet when the final tube of blood to be drawn is filling.
- Send the specimen to the laboratory as soon as possible.
Blood collection tubes come with a variety of colored stopper caps, and may contain additives. The following tubes are the most commonly used types:
- Red top. This tube contains no additives. It is used for a variety of tests, including blood typing and crossmatching.
- Tiger top or serum separator tube (SST). This tube contains a polymer gel and clot activator. When placed in a centrifuge, the serum is separated out. The SST is commonly used for blood chemistries.
- Lavender top. These tubes are used primarily for obtaining complete blood counts. They contain EDTA, an anticoagulant additive that chelates calcium.
- Dark green top. Green top tubes contain the anticoagulant heparin and are often used to obtain lithium and ammonia levels.
- Light blue top. The light blue top tubes contain sodium citrate, an agent that removes calcium, and are used to obtain protime (PT) and prothrombin time (PTT).
- Light gray top. This specimen tube contains sodium fluoride and potassium oxylate, antiglycolytic agents that preserve glucose for up to five days. The tube is used primarily to obtain glucose levels.
It is important that blood collection tubes be drawn in a certain order to avoid the cross-contamination of additives between tubes. It is recommended that tubes be drawn in the following order:
- Yellow-black stopper (blood culture tube).
- Red top.
- Light-blue top. This should not be the first tube drawn. If a coagulation assay is ordered alone, draw a non-additive tube first (red or SST), then draw the light-blue top tube.
- Additive tubes in the following order: dark green, lavender, light gray.
All tubes containing additives should be thoroughly mixed. Not doing so can result in inaccurate test results.
Venipuncture is not always possible or appropriate for the blood specimen required. In these cases, a fingerstick or heelstick may be the method of choice for obtaining the specimen.
The best locations for fingersticks are the third and fourth fingers of the patient's non-dominant hand. Avoid using the center, tip, or side of the finger. Avoid sticking areas that are thick or callused, where there is little soft tissue, or where the bone is close to the surface. Do not puncture a finger that is swollen, cyanotic (blue because of oxygen deficiency), or scarred. The fingerstick is done using a sterile lancet. The first drop of blood should be wiped away, as this first drop tends to contain extra fluid from the tissues. Instead of firmly milking the finger, it should only be gently massaged to gain drops of blood. Milking can squeeze tissue fluid into the drops of blood and alter laboratory results.
A heelstick is the preferred method of blood collection on a newborn baby or infant. In order to increase the flow of blood to the heel, the baby's heel should be prewarmed. (Avoid using too high a temperature as a baby's skin is easily injured.) The site to be punctured should be cleaned with alcohol, then dried with a dry cotton ball. The baby's foot should be held firmly to avoid sudden movements, then the side of the heel is punctured using a sterile lancet. Puncturing the center area of the heel should be avoided, as this can injure the underlying bone. Gentle pressure can be used to increase the flow of blood. To avoid diluting the specimen with excess tissue fluid, do not apply too much pressure.
After performing either a fingerstick or heelstick, a gauze pad or cotton ball should be applied for about a minute, making certain the bleeding has stopped.
The patient should be instructed about what blood tests have been ordered and why. Furthermore, explain the procedure and what the patient can expect. Ask the patient if anyone has had trouble drawing blood from him or her in the past. This may an alert to potential problems in finding an appropriate vein. Also ask the patient what position would be most comfortable for them when drawing the specimen. Venipuncture makes many patients nervous, and having them lie down may help them to relax and better tolerate the procedure.
After obtaining the ordered specimens, remove the needle from the vein and discard into a puncture-proof container. Pressure should be applied to the site for about a minute (longer if the patient is on any anticoagulants). After applying pressure, inspect the site for any signs of bleeding or hematomas. Apply a bandage to the site. The specimen containers should then be labeled and sent to the laboratory. Make sure the patient is comfortable and not experiencing any adverse affects before allowing them to get up.
Though venipuncture is routinely done and relatively safe, there are a few complications that can occur, including hematoma formation, hemolysis, and hemoconcentration. In addition, excessive bleeding can occur, and many patients have been known to faint during the procedure.
Health care team roles
Blood specimen collection is performed primarily by nurses and phlebotomists. The physician orders the laboratory tests. The nurse is responsible for instructing the patient regarding the procedure and assessing the patient's response. In addition, the nurse should be knowledgeable about the implications laboratory results may have on patient care.
Hemoconcentration— An increased concentration of larger molecules and formed elements in the blood.
Hemolysis— The destruction of red blood cells, which leads to the release of hemoglobin from within the red blood cells into the blood plasma.
Carroll, Patricia. "Only As Good As the Sample." RN 60 (September 1997).
Ernst, Dennis J. "Reduce Your Risk When You Draw Blood." RN 62 (December 1999).
Ernst, Dennis J. "Phlebotomy On Trial." Medical Laboratory Observer 31 (April 1999): 46.
Jagger, Janine and Jane Perry. "Making Routine Less Risky." Nursing 2000 (February 2000).