Blood gas test

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.[1] 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.[2]

Blood gas test
Purposemeasure blood gas tension values

Values measured
See also: Reference range

Blood samples for testing are taken from arterial blood by a radial artery puncture, and from venous blood by venipuncture. Samples of capillary blood are taken using a lancet and capillary action. Samples from capillaries from either the earlobe or the fingertip can be used to predict the arterial partial pressure of carbon dioxide, and the blood's pH. Samples from the earlobe are seen to be a more appropriate site for the prediction of the arterial partial pressure of oxygen.[3]

Blood gas tests also measure the levels of bicarbonate and of standard bicarbonate, of base excess, of oxygen saturation, and of pH. An arterial blood gas test is more often used.

Clinical significance

Blood gas tests can be used in the diagnosis of a number of acidosis conditions such as lactic, metabolic, and respiratory acidosis, diabetic ketoacidosis, and also of respiratory alkalosis.[1] Particularly, umbilical cord blood gas analysis can give an indication of preceding fetal hypoxic stress. In combination with other clinical information, normal paired arterial and venous cord blood gas results can usually provide a robust defence against a suggestion that an infant had an intrapartum hypoxic‐ischaemic event.[2]

Abnormal results may be due to a wide range of diseases, including poisoning and trauma as well as lung, kidney, or metabolic diseases. Drug overdose and uncontrolled diabetes may be determined from abnormal results.[4] Head or neck injuries or other injuries that affect breathing can also lead to abnormal results.[1]

References
  1. Seifter JL. Acid-base disorders. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 119
  2. Armstrong, L; Stenson, B J (1 November 2007). "Use of umbilical cord blood gas analysis in the assessment of the newborn". Archives of Disease in Childhood - Fetal and Neonatal Edition. 92 (6): F430–F434. doi:10.1136/adc.2006.099846. PMC 2675384. PMID 17951550.
  3. Zavorsky, Gerald S.; Cao, Jiguo; Mayo, Nancy E.; Gabbay, Rina; Murias, Juan M. (March 2007). "Arterial versus capillary blood gases: A meta-analysis". Respiratory Physiology & Neurobiology. 155 (3): 268–279. doi:10.1016/j.resp.2006.07.002. PMID 16919507.
  4. Dukić, Lora; Kopčinović, Lara Milevoj; Dorotić, Adrijana; Baršić, Ivana (15 October 2016). "Blood gas testing and related measurements: National recommendations on behalf of the Croatian Society of Medical Biochemistry and Laboratory Medicine". Biochemia Medica. 26 (3): 318–336. doi:10.11613/BM.2016.036. PMC 5082214. PMID 27812301.
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