Chlorides

Electrolyte“Chlorides”

Characteristics:

The major extracellular anion. Function: involve in maintaining osmolality, blood volume, and electrical neutrality. Median plasma and interstitial fluid concentrations of 103mmol/L Represents the largest fraction of the total inorganic anion concentration of 154mmol/L Represent the majority of osmotically active constituents of plasma 45-54mmol/L- concentration of Cl- in intracellular fluid of RBCs whereas on other tissues only

1mmol/L Most abundant anion in gastric and intestines In most process, it shifts secondarily to a movement of Na+ or HCO3

It is almost completely absorbed by the intestinal tract then filtered out by the glomerulus and passively reabsorbed, in conjunction w/ Na+, by the proximal tubules.

Excess is excreted in urine and sweat. Aldosterone is stimulated by excessive sweating making the sodium and chloride to be conserved.

Cl- maintains electrical neutrality in two ways:

1. Na+ is reabsorbed along with Cl- acts as the rate-limiting component so Na reabsorbtion is limited by the amount of Cl- available.

2. Chloride shift:

CO2 of plasma and RBC forms> carbonic acid which then splits to> H+HCO3- (bicarbonate)

*DeoxyHgb buffers H+ whereas the HCO3- diffuses out into the plasma

*consequently, Cl- diffuses into the red cell to maintain the electric balance of the cell

CLINICAL SIGNIFICANCE

*chloride disorders are often a result of the same causes that disturb Na+ levels because Cl- passively follows Na+. There are few exceptions:

1. HyperchloremiaI. May occur when there is an excess loss of HCO3 as a result of GI losses, RTA, or

metabolic acidosis.II. Dehydration

III. Conditions causing decrease renal blood flow as in Congestive Heart Failure (CHF)IV. Hyperchloremic acidosisV. Cystic fibrosis

VI. Hypercalcemia due to parathyroid hyperfunction

2. HypochloremiaI. May occur with excessive loss of Cl- from prolonged vomiting, diabetic ketoacidosis,

Aldosterone deficiency, or salt losing renal diseases such as pyelonephritis.II. In diarrhea, profuse sweating and certain endocrine disturbances wherein sodium loses

are excessive will also deplete Cl- in blood

Prepared by:PRINCESS ALEN I. AGUILAR


III. Hypochloremia alkalosis due to gastric juice secretion inhibition.IV. Salt-losing nephritis associated with chronic pyelonephritis

*Low serum levels of Cl- due to high serum HCO3-:

I. Compensated respiratory acidosisII. Metabolic alkalosis

DETERMINATION OF CHLORIDE

Methods:

1. ISEs (Ion-Selective Electrode)- most commonly used

Principle: Ion-exchange membrane is used to selectively bind Cl- ions

-Solvent polymeric membranes that incorporate quaternary ammonium salt anion-exchangers, such as tri-n-octylpropylammonium chloride decanol, are used to construct Cl -

selective electrodes in clinical analyzers

-These electrodes have been described to suffer from membrane instability and lot-to-lot inconsistency in selectivity to other anions.

-Anions that tend to be problematic are other halides and organic anions, such as SCN -, which can be particularly problematic because of their ability to solubilize in the polymeric organic membrane of these electrodes.

2. Amperometric-coulometric titration -are the most precise methods for measuring CI- over the entire range of concentrations displayed in body fluids.

Principle: Method using coulometric generation of silver ions (Ag+) which combine with Cl- to quantitate chloride concentration

Reaction: Ag2+ + 2Cl- AgCl2

-When all Cl- is bound to Ag+, excess or free Ag+ is used to indicate the endpoint. A timing device records the elapsed time between the start and stop of the Ag+ generation.

*DIGITAL (COTLOVECHLORIDOMETER) (Labconco Corporation) uses this principle in Cl- analysis

REAGENTS:

A. Nitric acid-Acetic acid Solution -serves as diluent and prevents reduction of precipitated AgCl2 at the sensing electrode

a. Nitric acid-provides good electrolyte conductivity

b. Acetic acid-makes the solution less polar, reducing the solubility of Silver Chloride.

B. Gelatine- equalizes the reaction rate over the entire electrode surface.



Considerations when using this method:

1. The method is subject to interferences by other halide ions, by CN- and SCN-

ions, by sulfhydryl groups, and by heavy metal contamination. Because samples are pre-diluted before analysis, these methods are also subject to the electrolyte exclusion effect.

2. Maintenance of the systems is crucial to proper operation; electrodes and reaction vials or chambers must be kept scrupulously clean and the proper shape and size of the Ag+ generating electrodes must be maintained.

3. Mercurimetric titration- one of the earliest method

Principle: A protein-free filtrate of specimen is titrated with mercuric nitrate solution in the presence of diphenylcarbazone as an indicator. Free Hg2+ combines with CI- to form soluble but essentially nonionized mercuric chloride:

Reaction: 2Cl + Hg(N03)2 -> HgCl2 + 2NO3-

-Excess Hg2+ reacts with diphenylcarbazone to form a blue-violet color complex

REAGENTS & RESULTS:

1. s-diphenylcarbazone- indicator2. Mercuric nitrate-titrating agent3. Mercuric chloride-end product4. Blue violet-end color

4. Spectrophotometric methods/ Whitethorne Titration/ Zall Color Reaction/Fisher and Gerarl

Principle: Chloride ions react with undissociated mercuric thiocyanate to form undissociated mercuric chloride and free thiocyanate ions. The thiocyanate ions react with ferric ion (Fe3*) to form the highly colored, reddish-brown complex of ferric thiocyanate with an absorption peak at 480 nm. Perchloric add increases the intensity of the red color.

Reaction:

Considerations in using this method:

High concentrations of globulins in the serum interfere in these methods because turbidity develops.

This reaction is also very temperature sensitive.

5. Sweat Chloride

Principle: the analysis of sweat for increased electrolyte concentration is used to confirm the diagnosis of cystic fibrosis (CF). It is caused by a defect in the cystic fibrosis transmembrane conductance regulator protein (CFTR), a protein that normally regulates electrolytes transport across epithelial membranes.



Performed in three phases:

1. Sweat stimulation by pilocarpine iontophoresis2. Collection of sweat3. Quali or quanti analysis of sweat Cl-, Na+, conductivity or osmolality

Reference range:

>60mmol/L = consistent with CF

40-60mmol/L = borderline

<40mmol/L = normal

Newborn = upto < 30mmol/L

6. Furic perchlorate (Fingerhut Method)

Principle: based on the formation of complex between ferric perchlorate and chloride. The complex formed is thought to be a chloro-complex of ferric ions which has a maximum absorbance at 340nm.

7. Colorimetry

PRACTICAL CONSIDERATIONS

Specimen:

Serum or plasma maybe used, w/ lithium heparin being the anticoagulant of choice

Hemolysis does not significantly affect the serum or plasma Cl- value Whole blood can be used with some analyzers In urine Cl-, 24 hour collection is the specimen of choice Fecal Cl- determination may be useful in diagnosis of congenital hypochloremic

alkalosis with hyperchloridorrhea (Increased excretion of Cl- in stool) o [Feces Cl-]= 180mmol/L with almost no Cl- being found in urine

Sweat is also suitable for analysis

Interferences:

Dirty pipette due to contamination Bromide and other halogens-react also in the procedure Hemolyzed sample will obscure to the end point giving as much as 15mmol/L

increase in the value Utilizing with the direct se of serum will five 2% increase because of protein

interferences. Sensitivity w/ pH of about 3-4.5 End point is not so stable (diphenylcarbazone- orange red will change to dark

cherry red) Should be kept in dark colored bottles otherwise it will deionized.

REFERENCE RANGES



Plasma/Serum: 98-107mmol/L (580-630 mg/dL)

*for neonates: 110mmol/L

*The spinal fluid Cl- concentrations are 15% higher than in serum

Urine: 110-250mmol/day, varies w/ diet

Feces: 3.2 + 0.7mmol/L


Chlorides

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