1. (C with a subscript indicating the substance removed)Removal of a substance from the blood, e.g., by renal excretion, expressed in terms of the volume flow of arterial blood or plasma that would contain the amount of substance removed per unit of time; measured in mL/min. Renal c. of any substance except urea or free water is calculated as the urine flow in mL/min multiplied by the urinary concentration of the substance divided by the arterial plasma concentration of the substance; normal human values are commonly expressed per 1.73 m2 body surface area. 2. A condition in which bodies may pass each other without hindrance, or the distance between bodies. 3. Removal of something from some place; e.g., “esophageal acid c.” refers to removal from the esophagus of some acid that has refluxed into it from the stomach, evaluated by the time taken for restoration of a normal pH in the esophagus.
- p-aminohippurate c. a good measure of renal plasma flow, which it slightly underestimates; when a low plasma concentration of p-aminohippurate (PAH) is maintained by intravenous infusion, the kidney extracts and excretes almost all of the PAH from the plasma before it reaches the renal vein.
- creatinine c. measurement of the c. of endogenous creatinine, used for evaluating the glomerular filtration rate (GFR).
- endogenous creatinine c. a term distinguishing measurements based on the creatinine normally present in plasma; since no infusion is necessary, an average value may be obtained by collecting urine for a long period, e.g., 24 hours.
- exogenous creatinine c. a term distinguishing measurements based on infusing creatinine intravenously to raise its plasma concentration and facilitate its accurate chemical determination.
- free water c. the amount of water excreted in the urine beyond that which would accompany the excreted solutes if the urine were isosmotic with plasma; it represents the loss of body water in excess of solute tending to raise body osmolality and making urine hyposmotic. Unlike other clearances, it is calculated by subtracting the osmolal c. from the actual volume of urine excreted per minute. A negative value for free water c. represents the amount of water that the body has reclaimed from isosmotic tubule fluid to make the urine hyperosmotic and to lower body osmolality.
- interocclusal c. SYN: freeway space.
- inulin c. an accurate measure of the rate of filtration through the renal glomeruli, because inulin filters freely with water and is neither excreted nor reabsorbed through tubule walls. Inulin is not a normal constituent of plasma and must be infused continously to maintain a steady plasma concentration and a steady rate of urinary excretion during the measurement. Inulin c. in a normal adult person is about 120 mL/min (range 100–150) per 1.73 m2 body surface area.
- isotope c. the rate at which an isotope is removed (usually by blood flow) from a tissue or organ such as the brain.
- maximum urea c. the urea c. when the urine flow exceeds 2 ml/min; normal value is about 75 mL blood/min per 1.73 m2 body surface area.
- mucociliary c. the movement of the mucous covering of the respiratory epithelium by the beating of cilia : rapid, forward (effective) stroke and slow, return (recovery) stroke.
- occlusal c. a condition in which the opposing occlusal surfaces may glide over one another without any interfering projection.
- osmolal c. the volume of urine that would be excreted per minute if the urinary solutes were accompanied by just enough water to make the urine isosmotic with plasma, i.e., so that the solute excretion did not change the osmolality of body fluids. To calculate it, the volume of urine excreted per minute is multiplied by the urinary osmolality (usually measured by freezing point depression) and divided by the plasma osmolality. Osmolal c. is less than actual urine flow when urine is hyposmotic and exceeds it when urine is hyperosmotic.
- standard urea c. the value obtained when the square root of the urine flow (when below 2 mL/min) is multiplied by the urine urea concentration and divided by the whole blood urea concentration; represents an old empirical adjustment for the effect of low urine flow on urea excretion; sometimes corrected for body size by dividing by some function of body weight or surface area. Later, plasma concentration was substituted for blood concentration in the calculation. The normal value is about 54 mL/min per 1.73 m2 in an adult person. SYN: Van Slyke formula.
- urea c. the volume of plasma (or blood) that would be completely cleared of urea by one minute's excretion of urine; originally calculated as urine flow multiplied by urine urea concentration divided by concentration of urea in whole blood rather than plasma, representing blood urea c. rather than plasma urea c..

* * *

clear·ance 'klir-ən(t)s n the volume of blood or plasma that could be freed of a specified constituent in a specified time (usu. one minute) by excretion of the constituent into the urine through the kidneys called also renal clearance

* * *

a quantitative measure of the rate at which waste products are removed from the blood by the kidneys. It is expressed in terms of the volume of blood that could be completely cleared of a particular substance in one minute.

* * *

clear·ance (klērґəns) 1. the process of removing a substance or an obstruction. 2. a quantitative measure of the rate at which a substance is removed from the blood by processes such as renal clearance, hepatic clearance, or hemodialysis; the volume of plasma that is completely cleared of the substance per unit time. Symbol C>. 3. the space existing between opposed structures.

Medical dictionary. 2011.

Игры ⚽ Поможем решить контрольную работу

Look at other dictionaries:

  • Clearance — Clear ance (kl[=e]r ans), n. 1. The act of clearing; as, to make a thorough clearance. [1913 Webster] 2. A certificate that a ship or vessel has been cleared at the customhouse; permission to sail. [1913 Webster] Every ship was subject to seizure …   The Collaborative International Dictionary of English

  • clearance — s.n. (med.) Raport între concentraţia sanguină a unei substanţe şi eliminarea prin urină. [pron. cliărăns. / < fr., engl. clearance – epurare]. Trimis de LauraGellner, 19.12.2004. Sursa: DN  CLEARANCE CLÍRĂNS/ s. n. raport între concentraţia… …   Dicționar Român

  • clearance — 1560s, action of clearing, from CLEAR (Cf. clear) + ANCE (Cf. ance). Meaning a clear space is from 1788. Meaning approval, permission (esp. to land or take off an aircraft) is from 1944, Amer.Eng.; national security sense recorded from 1948.… …   Etymology dictionary

  • clearance — [n1] permission for activity approval, authorization, consent, endorsement, goahead*, green light*, leave, okay, sanction, sayso*; concept 376 Ant. denial, grounding, refusal, veto clearance [n2] gap above something allowance, assart, defoliated… …   New thesaurus

  • clearance — [klir′əns] n. 1. an act or instance of clearing 2. the clear space or distance between moving objects or mechanical parts, or between a moving object and that which it passes through, over, under, etc. 3. official, esp. governmental,… …   English World dictionary

  • Clearance — Clearance. См. Допуск. (Источник: «Металлы и сплавы. Справочник.» Под редакцией Ю.П. Солнцева; НПО Профессионал , НПО Мир и семья ; Санкт Петербург, 2003 г.) …   Словарь металлургических терминов

  • clearance — index absolution, acquittal, amortization, collection (payment), composition (agreement in bankruptcy), compurgation, concession ( …   Law dictionary

  • clearance — *room, berth, play, elbowroom, leeway, margin …   New Dictionary of Synonyms

  • clearance — ► NOUN 1) the action or an act of clearing or the process of being cleared. 2) official authorization for something to take place. 3) clear space allowed for a thing to move past or under another …   English terms dictionary

  • clearance — clear/clearance Goods are cleared when HM Customs and Excise have accepted a declaration for them and formally released them for import or export. HM Customs & Revenue Glossary * * * clearance clear‧ance [ˈklɪərəns ǁ ˈklɪr ] noun [countable,… …   Financial and business terms

  • clearance — n. act of clearing away 1) slum clearance authorization 2) to give; receive clearance for 3) customs clearance 4) clearance to + inf. (the control tower gave the pilot clearance to land) space between parts 5) valve clearance certification of… …   Combinatory dictionary

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”