Blood Tests and Point Of Care Testing (POCT)
Blood carries out many vital functions as it circulates through the body. It transports oxygen from the lungs to other body tissue and carries away carbon dioxide. It carries nutrients from the digestive system to the cells of the body, and carries away the waste. Blood helps our body fight off pathogens and toxins, helps our body heal with its clotting ability, and regulates our body temperature. Blood tests have a wide range of uses and are one of the most common types of medical test.
Blood samples may be drawn from a vein, usually in the forearm. The puncture site is cleaned with an antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to restrict blood flow through the vein. This causes the vein below the tourniquet to fill with blood. A needle is inserted into the vein, and the blood is collected in a vial or syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
For example, a blood test can be used to:
- Assess your general state of health
- Check if you have an infection
- See how well certain organs, such as the liver and kidneys, are working
- Screen for certain genetic conditions
Most blood tests only take a few minutes to complete and are carried out at your GP surgery or local hospital by a doctor, nurse or phlebotomist (a specialist in taking blood samples).
Doctors rely on many different laboratory tests of blood to diagnose and monitor diseases. Some tests measure the components of blood itself, and others examine substances found in the blood stream to determine how other organs are functioning.
A CBC (complete blood cell count) is the most commonly performed blood test. It measures the two major basic components of blood: plasma, which is the clear, straw-coloured liquid portion, and red blood cells, white blood cells and platelets, which help in clotting. Red blood cells carry oxygen from the lungs to the tissues and carbon dioxide away. White blood cells help the body fight infection. In addition to determining the number of blood cells and platelets, the percentage of each type of white blood cell, and the content of haemoglobin (protein found in red blood cells), the CBC usually assesses the size and shape of red blood cells.
When a blood test is performed on an infant or child, a smaller amount of blood may be taken from the finger or earlobe.
Normal red blood cell counts vary, depending on the type of sample and your age and gender:
Men: 4.2 to 5.4 million red blood cells per microlitre of blood
Women: 3.6 to 5.0 million red blood cells per microlitre of blood
Children: 4.6 to 4.8 million red blood cells per microlitre of blood
Haemoglobin concentration correlates closely with the red blood cell count. Normal white blood cell counts range from 4,000 to 10,000 white blood cells per cubic millimetre of whole blood.
A low red blood cell or haemoglobin count may indicate anaemia, or severe bleeding. An elevated red cell or haemoglobin count may indicate polycythaemia, a rare blood disorder. Red blood cells that are abnormally shaped can also signal problems: sickle-shaped are characteristic of sickle cell disease, small red blood cells may indicate early iron deficiency, and large oval red blood cells suggest folic acid or vitamins B12 deficiency (pernicious anaemia).
The number of white blood cells may increase or decrease significantly in certain diseases. An elevated white blood cell count often indicates infection, such as an abscess, meningitis, appendicitis, or tonsillitis. A high count may also be caused by leukaemia or by dead tissue from burns, heart attack, or gangrene. A low white blood cell count indicates bone marrow problems.
Point of Care Testing
Point-of-care testing (POCT) or bedside testing is defined as medical diagnostic testing at or near the point of care. This differs from medical laboratory testing, which entails sending specimens away from the point of care and then waiting hours or days to learn the results, during which time care must continue without the desired information. Many devices are now available to carry out testing at the actual 'point of care' thus, avoiding delays in diagnosis. These range from simple battery operated strip devices, to more complex bench-top devices.
Point of care diagnostics can integrate biochemical testing alongside physiologic measurements. Blood Analysis can be carried out by the patient's bedside very quickly, and using low blood sample amounts. POCT may deliver results for blood gases, electrolytes, chemistries, haematocrit, and other calculated parameters.
Some Blood Analysis Portals use disposable cartridges containing the same technology as large, laboratory bench-top equipment, only in miniature. Immediacy of diagnostics test information is essential for precise titration and, ultimately, for improved therapy in adult; paediatric; neonatal intensive care; operating theatre and post-anaesthesia; and emergency settings - environments where patient care requires immediate turnaround of blood test results for clinical decision making. Yet, traditional laboratory blood testing processes experience inherent delays from the time a doctor orders the tests until results are delivered. With POCT, neither the sample nor the caregiver leaves the patient's side.
Over many decades, testing has continued to move away from the laboratory and more towards the point of care. The driving notion behind POCT is to bring the test conveniently and immediately to the patient. This increases the likelihood that the patient, doctor, and care team will receive the results quicker, which allows for immediate clinical management decisions to be made. POCT can include: blood glucose testing, blood gas and electrolytes analysis, rapid coagulation testing, rapid cardiac markers diagnostics, drugs of abuse screening, urine strips testing, pregnancy testing, faecal occult blood analysis, food pathogens screening, haemoglobin diagnostics, infectious disease testing and cholesterol screening.
POCT is often accomplished through the use of transportable, portable, and handheld instruments and test kits. Small bench analyzers or fixed equipment can also be used when a handheld device is not available—the goal is to collect the specimen and obtain the results in a very short period of time at or near the location of the patient so that the treatment plan can be adjusted as necessary before the patient leaves. Cheaper, faster, and smarter POCT devices have increased the use of POCT approaches by making it cost-effective for many diseases.
Additionally, it is very desirable to measure various analytes (a substance whose chemical constituents are being identified and measured) simultaneously in the same specimen, allowing a rapid, low-cost, and reliable quantification. Therefore, multiplexed point-of-care testing is becoming more common and important for medical diagnostics, and it is likely that this trend will continue in the coming decades.
Edited by Dr John Sandham