Blood Test
Question 1. What is venepuncture?
Venepuncture means collection of blood by puncturing a vein with a needle. The most common reason for collecting blood is for investigating diseases. Blood can also be collected for performing cross-match in blood/blood product transfusion and also as a form of treatment for blood diseases, for example, too much iron in blood (iron-overload).
Venepuncture is a special technique performed by well trained and experienced health personnel (phlebotomist). In many countries, a health worker is allowed to collect blood only upon successfully completion of Blood Collection Certification Course. In PNG, many health workers collect blood without obtaining a certification for Venepuncture but using the basic knowledge acquired during their under-graduate training supplemented by practical sessions taught by senior health workers.
Question 2. How is Venepuncture performed?
Blood collection involves use of correct sterile technique to avoid infection, correct needle size and syringes or vacuum tube system, appropriate tubes for requested test, correct technique in handling of needle and syringe combinations, and identification of appropriate veins for Venepuncture.
You should be seated comfortably on a chair or lying down on bench/bed prior to blood collection. A healthy and visible vein is first identified. A tourniquet or arm band may be applied to improve visibility of vein. Skin is then cleansed with alcohol swab or iodine over the site of puncture to avoid introducing infection. When the skin is dry, a needle and syringe combination of correct sizes is used to collect blood. Once blood is collected and is needle removed, a small pressure is applied to the Venepuncture site with cotton wool to stop further bleeding. (DONOT bend your elbow! This will cause swelling). A dressing or Band-Aid may be applied when completed.
When blood is collected by untrained or poorly trained staff, complications can occur. Some signs of poor technique include repeated attempts, painful procedure, swelling over puncture site, spillage of blood and blood stains on bench and table, and rejected samples unsuitable for laboratory analysis.
Question 3. Where is the common site for Venepuncture?
Venepuncture is commonly done in the front of the elbow area called antecubital fossa. Depending on health and visibility of veins other sites such as back of hand (dorsum) and forearm veins may be used. In children, heel of feet or leg veins are also used.
Question 4. How much blood is taken from me?
The amount of blood taken from an individual depends on reason for Venepuncture. Commonly only two or three tubes each with 4-10ml capacity is taken. Hence, only 40 to 50mls of blood will be taken in any Venepuncture session for the standard blood test. A tube of blood is enough to do tests for kidney disease, liver disease, infections, cholesterol and many more. In children, even smaller volumes as small as 2-3mls of blood can be taken. Off-course if you donate blood for transfusion 250 to 300mls of blood is taken.
Question 5. Can I become anaemic from repeated Venepuncture?
Anaemia due to repeated Venepuncture for blood testing is very rare. However, this can happen in newborn babies as their blood volume is much smaller than in children and adults. Off-course one can become anaemic with repeated blood donation because the volume of blood taken here is 30-50x that given for blood testing.
Question 6. My doctor failed to find my vein quickly and I was pierced repeatedly. Why?
Failure to collect blood and repeated attempts could result from poor technique by uncertified phlebotomist or staff. It can also happen if the vein is collapsed (cold weather/dehydration) or is too deep and not visible as happens in over-weight person, children and the elderly. Sometimes a gentle rub to the vein or application of warm pack will ensure better vein access.
Question 7. What do I have to do before Venepuncture?
No special preparation is required for most blood tests prior to blood collection. However, some blood tests such as for lipid and glucose testing will require fasting blood samples. Fasting involves taking nothing except plain water beginning mid-night until blood is collected next morning (for 8-10hours). If specific preparation is required, you will be told before you present for blood collection. It is important to tell your phlebotomist if you have any allergies particularly to tapes and iodine in advance.
Question 8. Is Venepuncture painful?
Venepuncture will not cause much pain if done properly by a trained person. Occasionally a small stinging sensation will be felt especially when needle is inserted or withdrawn. This is more likely if the skin is still moist when needle is inserted or if inappropriately large needle is used on small vein. Blood taken in the front of elbow (antecubital fossa) is less painful than that taken on other sites.
Question 9. I have excessive fear of needle. How can I tolerate blood collection?
It is normal to have some fear about needle but for some individuals the fear can be so bad that Venepuncture cannot be performed without patient collapsing or becoming very anxious. Discuss this with your doctor prior to blood collection. Treatment is available to assist you with this.
Question 10. What are the dangers of Venepuncture?
With proper training dangers of Venepuncture are minimal. Some problems that can arise include collapse of patient, light-headedness, pain, swelling, bleeding, and infection. Rarely allergic reactions can occur from iodine or dressing tapes used.
Question 11. Why is it dangerous to collect blood while patient is standing?
You should not allow blood collection while standing however confident you may be. A trained Phlebotomist will always ensure that you are well seated or lying down while Venepuncture is being performed. You are more likely to collapse or faint while standing due to drop in blood pressure provoked by pain and sight of blood or needle. The phlebotomist will have needles and tubes in his/her hand and no one will be there to catch you when you suddenly turn pale/white and fall down without any warning.
Question 12. My blood test is negative, why am I still feeling sick?
Your test can be negative sometimes, yet you could still have the disease. Not all diseases can be diagnosed by blood tests alone. Many diseases require doctors to perform additional tests such as x-rays and scans (e.g., tuberculosis infection). More often doctors use their ‘expert instinct’ listening to your story and performing a physical examination on you to make a correct diagnosis and treat you even if your test result is negative.
There is an inherent feature of medical tests called specificity and sensitivity. Sensitive is the ability of the medical tests to pick up disease when it is present whereas specificity is the discriminating ability of the test to differentiate one type of sickness from other similar illnesses. Many medical tests have low sensitivity and specificity. In other words, you can still have false positive as well as false negative results. For example, you can still have malaria without showing positive malaria tests if the parasite numbers in blood are too low for detection. Blood test result is just one of the indicators used to make a diagnosis of your illness.
Blood results can be negative if you are tested very early during the course of illness. For example, you can still have typhoid or HIV infection but show negative blood test particularly if your test is done early (less than 7-10 days) during the stage called ‘window- period’ .
Question 13. My blood test is abnormal. Why am I feeling normal?
Some diseases are silent and patients do not have any complaints. However, patients often have symptoms that may seem normal to them when specifically questioned. This is true for diseases such as diabetes and high cholesterol. It is estimated that 50% of patients with diabetes live without knowing that they have diabetes. Many patients with high cholesterol and hepatitis B virus and HIV infections also do not have complaints. The only way to make a diagnosis of asymptomatic problem is by doing a blood test.
