A blood test is a laboratory analysis performed on a blood sample that is usually extracted from a vein in the arm using a hypodermic needle, or via fingerprick. Multiple tests for specific blood components, such as a glucose test or a cholesterol test, are often grouped together into one test panel called a blood panel or blood work. Blood tests are often used in health care to determine physiological and biochemical states, such as disease, mineral content, pharmaceutical drug effectiveness, and organ function. Typical clinical blood panels include a basic metabolic panel or a complete blood count. Blood tests are also used in drug tests to detect drug abuse.
A venipuncture is useful as it is a minimally invasive way to obtain cells and extracellular fluid (plasma) from the body for analysis. Blood flows throughout the body, acting as a medium that provides oxygen and nutrients to tissues and carries waste products back to the excretory systems for disposal. Consequently, the state of the bloodstream affects or is affected by, many medical conditions. For these reasons, blood tests are the most commonly performed medical tests. [1]
If only a few drops of blood are needed, a fingerstick is performed instead of a venipuncture. [2]
Indwelling arterial, central venous and peripheral venous lines can also be used to draw blood. [3]
Phlebotomists, laboratory practitioners and nurses are those in charge of extracting blood from a patient. However, in special circumstances, and/or emergency situations, paramedics and physicians extract the blood. Also, respiratory therapists are trained to extract arterial blood to examine arterial blood gases. [4] [5]
A basic metabolic panel measures sodium, potassium, chloride, bicarbonate, blood urea nitrogen (BUN), magnesium, creatinine, glucose, and sometimes calcium. Tests that focus on cholesterol levels can determine LDL and HDL cholesterol levels, as well as triglyceride levels. [6]
Some tests, such as those that measure glucose or a lipid profile, require fasting (or no food consumption) eight to twelve hours prior to the drawing of the blood sample. [7]
For the majority of tests, blood is usually obtained from the patient's vein. Other specialized tests, such as the arterial blood gas test, require blood extracted from an artery. Blood gas analysis of arterial blood is primarily used to monitor carbon dioxide and oxygen levels related to pulmonary function, but is also used to measure blood pH and bicarbonate levels for certain metabolic conditions. [8]
While the regular glucose test is taken at a certain point in time, the glucose tolerance test involves repeated testing to determine the rate at which glucose is processed by the body. [9]
Blood tests are also used to identify autoimmune diseases and Immunoglobulin E-mediated food allergies (see also Radioallergosorbent test). [10] : 1118
Blood tests results should always be interpreted using the ranges provided by the laboratory that performed the test. Example ranges are shown below.
Test [11] [12] | Low | High | Unit | Comments |
---|---|---|---|---|
Sodium (Na) | 134 | 145 | mmol/L | |
Potassium (K) | 3.5 | 5.0 | mmol/L | |
Urea | 2.5 | 6.4 | mmol/L | Blood urea nitrogen (BUN) |
Urea | 15 | 40 | mg/dL | |
Creatinine - male | 62 | 115 | μmol/L | |
Creatinine - female | 53 | 97 | μmol/L | |
Creatinine - male | 0.7 | 1.3 | mg/dL | |
Creatinine - female | 0.6 | 1.2 | mg/dL | |
Glucose (fasting) | 3.9 | 5.8 | mmol/L | See also glycated hemoglobin |
Glucose (fasting) | 70 | 120 | mg/dL | |
Upon completion of a blood test analysis, patients may receive a report with blood test abbreviations. Examples of common blood test abbreviations are shown below.
Abbreviation [13] [14] | Stands for | Description |
---|---|---|
HDL | High Density Lipoprotein | Level of "good cholesterol" in the blood (ratio of HDL:LDL is usually more significant than actual values) |
LDL | Low Density Lipoprotein | Level of "bad cholesterol" in the blood (ratio of HDL:LDL is usually more significant than actual values) |
PV | Plasma Viscosity | Plasma Viscometry (PV) is the measurement of the viscosity of blood plasma. The result is a number given in milliPascal seconds (m.Pas.s) – known as the PV, or plasma viscosity. |
CRP | C-Reactive Protein | Level of inflammation with the body. If the immune system is fighting an infection or illness, CRP will be higher. |
CBC (UK: FBC) | Complete Blood Count (UK: Full Blood Count) | Analysis of 15 different blood test readings to provide information about overall health. |
TSH | Thyroid-stimulating hormone | Thyroid regulates the function of metabolism. Low levels can lead to weight loss, while high levels lead to weight gain. |
PTH | Parathyroid hormone | Regulates serum calcium |
ESR | Erythrocyte Sedimentation Rate | Indicates the time it takes for red blood cells to move down a tube. This shows signs of inflammation within a body. |
INR | International Normalized Ratio | This is a blood clotting test. |
LFT | Liver Function Test | This test reveals the levels of waste products, enzymes and proteins that are processed by the liver. |
U+E | Urea and Electrolytes | This test is performed to measure the function of kidney. |
CMP | Comprehensive Metabolic Panel | This analysis provides an overall picture of the metabolism and chemical balance of the body. |
WBC | White Blood Cell Count | The level of white blood cells. |
RBC | Red Blood Cell Count | The level of red blood cells. |
HBC | Hemoglobin | Level of hemoglobin molecules. |
HCT | Hematocrit | Similar to RBC but in percentage. |
PLT | Platelets | Platelets levels in the blood. |
In 2008, scientists announced that the more cost effective saliva testing could eventually replace some blood tests, as saliva contains 20% of the proteins found in blood. [15] Saliva testing may not be appropriate or available for all markers. For example, lipid levels cannot be measured with saliva testing.
In February 2011, Canadian researchers at the University of Calgary's Schulich School of Engineering announced a microchip for blood tests. Dubbed a microemulsion, a droplet of blood captured inside a layer of another substance. It can control the exact size and spacing of the droplets. The new test could improve the efficiency, accuracy, and speed of laboratory tests while also doing it cheaply. [16]
In March 2011, a team of researchers from UC Berkeley, DCU and University of Valparaíso have developed lab-on-a-chip that can diagnose diseases within 10 minutes without the use of external tubing and extra components. It is called Self-powered Integrated Microfluidic Blood Analysis System (SIMBAS). It uses tiny trenches to separate blood cells from plasma (99 percent of blood cells were captured during experiments). Researchers used plastic components, to reduce manufacturing costs. [17] [18]
In biology, homeostasis is the state of steady internal physical and chemical conditions maintained by living systems. This is the condition of optimal functioning for the organism and includes many variables, such as body temperature and fluid balance, being kept within certain pre-set limits. Other variables include the pH of extracellular fluid, the concentrations of sodium, potassium, and calcium ions, as well as the blood sugar level, and these need to be regulated despite changes in the environment, diet, or level of activity. Each of these variables is controlled by one or more regulators or homeostatic mechanisms, which together maintain life.
The following is a glossary of diabetes which explains terms connected with diabetes.
The glucose tolerance test is a medical test in which glucose is given and blood samples taken afterward to determine how quickly it is cleared from the blood. The test is usually used to test for diabetes, insulin resistance, impaired beta cell function, and sometimes reactive hypoglycemia and acromegaly, or rarer disorders of carbohydrate metabolism. In the most commonly performed version of the test, an oral glucose tolerance test (OGTT), a standard dose of glucose is ingested by mouth and blood levels are checked two hours later. Many variations of the GTT have been devised over the years for various purposes, with different standard doses of glucose, different routes of administration, different intervals and durations of sampling, and various substances measured in addition to blood glucose.
Clinical chemistry is a division in medical laboratory sciences focusing on qualitative tests of important compounds, referred to as analytes or markers, in bodily fluids and tissues using analytical techniques and specialized instruments. This interdisciplinary field includes knowledge from medicine, biology, chemistry, biomedical engineering, informatics, and an applied form of biochemistry.
Reference ranges for blood tests are sets of values used by a health professional to interpret a set of medical test results from blood samples. Reference ranges for blood tests are studied within the field of clinical chemistry, the area of pathology that is generally concerned with analysis of bodily fluids.
In medicine, venipuncture or venepuncture is the process of obtaining intravenous access for the purpose of venous blood sampling or intravenous therapy. In healthcare, this procedure is performed by medical laboratory scientists, medical practitioners, some EMTs, paramedics, phlebotomists, dialysis technicians, and other nursing staff. In veterinary medicine, the procedure is performed by veterinarians and veterinary technicians.
The blood sugar level, blood sugar concentration, blood glucose level, or glycemia is the measure of glucose concentrated in the blood. The body tightly regulates blood glucose levels as a part of metabolic homeostasis.
An arterial blood gas (ABG) test, or arterial blood gas analysis (ABGA) measures the amounts of arterial gases, such as oxygen and carbon dioxide. An ABG test requires that a small volume of blood be drawn from the radial artery with a syringe and a thin needle, but sometimes the femoral artery in the groin or another site is used. The blood can also be drawn from an arterial catheter.
A blood gas test or blood gas analysis tests blood to measure blood gas tension values, it also measures blood pH, and the level and base excess of bicarbonate. The source of the blood is reflected in the name of each test; arterial blood gases come from arteries, venous blood gases come from veins and capillary blood gases come from capillaries. The blood gas tension levels of partial pressures can be used as indicators of ventilation, respiration and oxygenation. Analysis of paired arterial and venous specimens can give insights into the aetiology of acidosis in the newborn.
Acidosis is a biological process producing hydrogen ions and increasing their concentration in blood or body fluids. pH is the negative log of hydrogen ion concentration and so it is decreased by a process of acidosis.
Hypercholesterolemia, also called high cholesterol, is the presence of high levels of cholesterol in the blood. It is a form of hyperlipidemia, hyperlipoproteinemia, and dyslipidemia.
Venous blood is deoxygenated blood which travels from the peripheral blood vessels, through the venous system into the right atrium of the heart. Deoxygenated blood is then pumped by the right ventricle to the lungs via the pulmonary artery which is divided in two branches, left and right to the left and right lungs respectively. Blood is oxygenated in the lungs and returns to the left atrium through the pulmonary veins.
In medicine, some blood tests are conducted on capillary blood obtained by fingerstick. The site, free of surface arterial flow, where the blood is to be collected is sterilized with a topical germicide, and the skin pierced with a sterile lancet. After a droplet has formed, capillary blood is captured in a capillary tube. Blood cells drawn from fingersticks have a tendency to undergo hemolysis, especially if the finger is "milked" to obtain more blood.
The main goal of diabetes management is to keep blood glucose (BG) levels as normal as possible. If diabetes is not well controlled, further challenges to health may occur. People with diabetes can measure blood sugar by various methods, such as with a BG meter or a continuous glucose monitor, which monitors over several days. Glucose can also be measured by analysis of a routine blood sample. Usually, people are recommended to control diet, exercise, and maintain a healthy weight, although some people may need medications to control their blood sugar levels. Other goals of diabetes management are to prevent or treat complications that can result from the disease itself and from its treatment.
An embolus, is described as a free-floating mass, located inside blood vessels that can travel from one site in the blood stream to another. An embolus can be made up of solid, liquid, or gas. Once these masses get "stuck" in a different blood vessel, it is then known as an "embolism." An embolism can cause ischemia—damage to an organ from lack of oxygen. A paradoxical embolism is a specific type of embolism in which the embolus travels from the right side of the heart to the left side of the heart and lodges itself in a blood vessel known as an artery. Thus, it is termed "paradoxical" because the embolus lands in an artery, rather than a vein.
In medicine, a biomarker is a measurable indicator of the severity or presence of some disease state. It may be defined as a "cellular, biochemical or molecular alteration in cells, tissues or fluids that can be measured and evaluated to indicate normal biological processes, pathogenic processes, or pharmacological responses to a therapeutic intervention." More generally a biomarker is anything that can be used as an indicator of a particular disease state or some other physiological state of an organism. According to the WHO, the indicator may be chemical, physical, or biological in nature - and the measurement may be functional, physiological, biochemical, cellular, or molecular.
Vascular disease is a class of diseases of the vessels of the circulatory system in the body, including blood vessels – the arteries and veins, and the lymphatic vessels. Vascular disease is a subgroup of cardiovascular disease. Disorders in this vast network of blood and lymph vessels can cause a range of health problems that can sometimes become severe, and fatal. Coronary heart disease for example, is the leading cause of death for men and women in the United States.
Oxygen saturation is the fraction of oxygen-saturated haemoglobin relative to total haemoglobin in the blood. The human body requires and regulates a very precise and specific balance of oxygen in the blood. Normal arterial blood oxygen saturation levels in humans are 96–100 percent. If the level is below 90 percent, it is considered low and called hypoxemia. Arterial blood oxygen levels below 80 percent may compromise organ function, such as the brain and heart, and should be promptly addressed. Continued low oxygen levels may lead to respiratory or cardiac arrest. Oxygen therapy may be used to assist in raising blood oxygen levels. Oxygenation occurs when oxygen molecules enter the tissues of the body. For example, blood is oxygenated in the lungs, where oxygen molecules travel from the air and into the blood. Oxygenation is commonly used to refer to medical oxygen saturation.
In medicine, sampling is gathering of matter from the body to aid in the process of a medical diagnosis and/or evaluation of an indication for treatment, further medical tests or other procedures. In this sense, the sample is the gathered matter, and the sampling tool or sampler is the person or material to collect the sample.
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