Blood test

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A venipuncture performed using a vacutainer

A blood test is a laboratory analysis performed on a blood sample that is usually extracted from a vein in the arm using a 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[1] 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.

Extraction[edit]

Venipuncture is useful as it is a minimally invasive way to obtain cells and extracellular fluid (plasma) from the body for analysis. Since blood flows throughout the body, acting as a medium for providing oxygen and nutrients, and drawing waste products back to the excretory systems for disposal, 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.[2]

If only a few drops of blood are needed, a fingerstick is performed instead of drawing blood from a vein.[3]

Phlebotomists, laboratory practitioners and nurses are those charged with patient blood extraction. However, in special circumstances, and emergency situations, paramedics and physicians sometimes extract blood. Also, respiratory therapists are trained to extract arterial blood to examine arterial blood gases.[4][5]

Types of blood tests[edit]

Samples of human blood collected for testing. The barcodes contain information that is used to identify the individual from whom the sample was taken and the blood test requested.

Biochemical analysis[edit]

A basic metabolic panel measures sodium, potassium, chloride, bicarbonate, blood urea nitrogen (BUN), magnesium, creatinine, glucose, and sometimes includes calcium. Blood tests focusing on cholesterol levels can determine LDL and HDL cholesterol levels, as well as triglyceride levels.[6]

Some blood 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 blood tests, blood is usually obtained from the patient's vein. However, other specialized blood tests, such as the arterial blood gas, 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 it 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]

Normal ranges[edit]

Blood tests results should always be interpreted using the ranges provided by the laboratory that performed the test. Example ranges are shown below:

Test[10][11] Low High Unit Comments
Sodium (Na) 136 145 mmol/L
Potassium (K) 3.5 5.0 mmol/L
Urea 2.5 6.4 mmol/L BUN - blood urea nitrogen
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

Molecular profiles[edit]

Cellular evaluation[edit]

Future alternatives[edit]

Saliva tests[edit]

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.[12]

Microemulsion[edit]

In February 2011 Canadian researchers 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. The microchip costs $25, whereas the robotic dispensers currently in use cost around $10,000. [13]

In 2013, Theranos Corporation announced a partnership with Walgreens to provide blood panels supporting nearly 200 tests, that require only a single capsule-sized lab vial of blood. Results are available in less than four hours. Blood is drawn with a finger stick, rather than a needle in the arm. The diagnostic technology is integrated and cross-calibrated to ensure consistent results.[14]

SIMBAS[edit]

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.[15][16]

See also[edit]

References[edit]

  1. ^ "Blood Panel". Retrieved 2013-10-28. 
  2. ^ "Venipuncture - the extraction of blood using a needle and syringe". Retrieved June 21, 2012. 
  3. ^ MacLennan CA, van Oosterhout JJ, White SA, Drayson MT, Zijlstra EE, Molyneux ME (July 2007). "Finger-prick blood samples can be used interchangeably with venous samples for CD4 cell counting indicating their potential for use in CD4 rapid tests". AIDS (London, England) 21 (12): 1643–5. doi:10.1097/QAD.0b013e32823bcb03. PMC 2408852. PMID 17630562. 
  4. ^ Aaron SD, Vandemheen KL, Naftel SA, Lewis MJ, Rodger MA (2003). "Topical tetracaine prior to arterial puncture: a randomized, placebo-controlled clinical trial". Respir Med. 97 (11): 1195–1199. doi:10.1016/S0954-6111(03)00226-9. PMID 14635973. 
  5. ^ "Michigan careers". Michigan.gov. 2010-01-05. Retrieved 2011-08-09. 
  6. ^ Belargo, Kevin. "Cholesterol Levels". Manic EP. Retrieved 17 January 2012. 
  7. ^ "Fasting blood samples". NHS UK. Retrieved June 21, 2012. 
  8. ^ "Blood gases". NHS UK. Retrieved June 21, 2012. 
  9. ^ "Glucose tolerance test". Medline. Retrieved June 21, 2012. 
  10. ^ C. A. Burtis and E. R. Ashwood, Tietz Textbook of Clinical Chemistry (1994) 2nd edition, ISBN 0-7216-4472-4
  11. ^ "Blood tests normal ranges". Monthly Prescribing Reference. Retrieved June 21, 2012. 
  12. ^ "Press TV - Saliva test to substitute blood test". Presstv.ir. Retrieved 2011-08-09. 
  13. ^ New method for blood tests could radically cut costs[dead link]
  14. ^ "Small, Fast and Cheap, Theranos Is the Poster Child of Med Tech — and It’s in Walgreen’s". Singularity Hub. 2013-11-18. Retrieved 2013-12-07. 
  15. ^ Taylor, Kate (2011-03-18). "Blood analysis chip detects diseases in minutes". Retrieved 2011-03-26. 
  16. ^ Dailey, Jessica (2011-03-22). "New SIMBAS Blood Analysis Biochip Can Diagnose Diseases In Minutes". Inhabitat.com. Retrieved 2011-03-26. 

External links[edit]