Venipuncture Explained
Venipuncture in medicine is not just sampling of venous blood, but also covers the process of obtaining intravenous access specifically for intravenous therapy. It is performed by medical practitioners, paramedics, dialysis technicians, medical laboratory scientists and other nursing staff. Veterinarians and veterinary technicians also perform venipuncture. When it comes to blood draw, it is usually performed by phlebotomists.
Blood specimens are instrumental in helping clinicians and other healthcare professionals to collect data that can help interpret a wide variety of clinical signs and symptoms. This makes blood analysis a vital diagnostic tool. Aside from diagnostic purposes, blood draw is performed to monitor levels of blood components, remove blood due to excess levels of iron, to collect blood that will be later used for transfusion, and to administer therapeutic treatments, such as chemotherapy.
According to Medical Laboratory Scientist, blood draw is performed for the following reasons:
- Complete blood count (WBC, RBC, Hct, Hb, plt, RDW),
- Anemia
- Cancers and other disorders
- Infections (both increased WBC and actual bacterial organisms)
- Glucose/sodium/potassium/etc. levels
- Cross-match blood for a possible transfusion
- Cholesterol check
- Protein Levels check
Materials and Procedures
Blood can be drawn in many ways, but usually from the median cubital vein. The entire process requires several tools and involves different steps. (check the order of draw for more info)
Depending on the patient's age, the test required and equipment available, the method used could vary. In the US, UK, and Hong Kong, blood collection is usually done with an evacuated tube system that consists of a hypodermic needle, plastic hub and a vacuum tube. In some developing countries, syringe with a needle or with a butterfly needle is commonly used.
Venipuncture in children may require the use of methods or medications that can reduce pain. The use of lidocaine iontophoresis is said to be safe and effective for venipuncture in children 6 to 17 years old. Unfortunately, it cannot be used to all the children.
The syringe-needle technique for venipuncture is commonly used on people who are difficult draws, have fragile veins, obese, severely burned, elderly and oncology patients. This procedure is preferred under the circumstances because the syringe is manually operated. This means the amount of suction applied can be easily controlled.
Collecting blood samples from animals is an entirely different story. It is categorized in three procedures, depending on the animal being drawn. Collecting specimen from the tail vein of a rat, for example, involves blood collection that requires anesthesia. There's also blood collection that does not require anesthesia and terminal procedure, such as cardiac puncture on a rabbit or through the orbital sinus of a rat.
While there are plenty of books and online resources where venipuncture is explained thoroughly, checking out videos would prove to be more effective, especially because memory retention is higher when viewing visual materials. Fortunately, there are many venipuncture videos available online.
In the Pathology Thread in the University of Virginia School of Medicine page, you will see a video of a standard venipuncture procedure. There is also a set of related videos on DNA Tube. Aside from drawing blood samples, there are also videos on arterial blood gases, automated blood analyzer and determining blood types. Nursing 101, the “video central for nursing skills”, also offers videos on different venipuncture tips and techniques. There are phlebotomy clips of blood draw using a straight needle, another for butterfly needle, and using a syringe.
