Information about Anion Gap

The anion gap is used to aid in the differential diagnosis of metabolic acidosis.

Calculation

It is calculated by subtracting the serum concentrations of chloride and bicarbonate (anions) from the concentrations of sodium plus potassium (cations):

= ( [Na⁺]+[K⁺] ) - ( [Cl^-]+[HCO₃^-] )

However, for daily practice, the potassium is frequently ignored, leaving the following equation:

= ( [Na⁺] ) - ( [Cl^-]+[HCO₃^-] )

Uses

The anion gap is representative of the unmeasured anions in the plasma, and these anions are affected differently based on the type of metabolic acidosis. The primary function of the anion gap measurement is to allow a clinician to narrow down the possible causes of a patient's metabolic acidosis. For example, if a patient presents with metabolic acidosis, but a normal anion gap, then conditions that cause a high anion gap can be ruled out as being the cause of the acidosis.

Normal value ranges

In the past, methods for the measurement of the anion gap consisted of colorimetry for [HCO₃^-] and [Cl^-] as well as flame photometry for [Na⁺] and [K⁺]. Thus normal reference values ranged from 8 to 16 mmol/L plasma when not including [K⁺] and from 10 to 20 mmol/L plasma when including [K⁺]. Some specific sources use 15^[1] and 8-16 mEq/L.^[2][3]

Modern analysers make use of ion-selective electrodes which give a normal anion gap as <11 mmol/L. Therefore according to the new classification system a high anion gap is anything above 11mmol/L and a normal anion gap is between 3-11 mmol/L.^[4]

Interpretation and causes

Anion gap can be classified as either high, normal or, in rare cases, low. A high anion gap indicates that there is loss of HCO₃^- without a subsequent increase in Cl^-. Electroneutrality is maintained by the increased production of anions like ketones, lactate, PO₄^-, and SO₄^-; these anions are not part of the anion-gap calculation and therefore a high anion gap results. In patients with a normal anion gap the drop in HCO₃^- is compensated for by an increase in Cl^- and hence is also known as hyperchloremic acidosis.

High anion gap

The bicarbonate lost is replaced by an unmeasured anion and thus you will see a high anion gap.

• Lactic acidosis
• Ketoacidosis
• Diabetic ketoacidosis
• Alcohol abuse
• Toxins:
• Ethanol
• Ethylene glycol
• Lactic acid
• Methanol
• Paraldehyde
• Aspirin
• Cyanide, coupled with elevated venous oxygenation
• Iron
• isoniazid

The mnemonic "MUDPILES" is used to remember the causes of a high anion gap.

M - methanol/metformin
U - uremia
D - diabetic ketoacidosis
P - paraldehyde/propylene glycol
I - Infection/ischemia/isoniazid
L - lactate
E - ethylene glycol/ethanol
S - salicylates/starvation

Some people, especially those not in the emergency room, find the mnemonic KIL-U easier to remember and also more useful clinically:

K - Ketones
I - Ingestion
L - lactic acid
U - uremia


All of the components of "mudpiles" are also covered with the "KIL-U" device, with the bonus that these are things that can kill you.

Ketones: more straightforward than remembering diabetic ketosis and starvation ketosis, etc.

Ingestion: methanol, metformin, paraldehyde, propylene glycol, isoniazid, ethylene glycol, ethanol, and salicilates are covered by ingestion. These can be thought of as a single group: "ingestions" during the initial consideration, especially when not triaging a patient in the emergency room.

Lactate: including that caused by infection and shock

Normal anion gap (hyperchloremic acidosis)

Usually the HCO₃^- lost is replaced by a chloride anion, and thus there is a normal anion gap.

• Gastrointestinal loss of HCO₃^- (i.e. diarrhea) (note: vomiting causes hypochloraemic alkalosis)
• Renal loss of HCO₃^- (i.e. proximal renal tubular acidosis)
• Renal dysfunction (i.e. renal failure, hypoaldosteronism, distal renal tubular acidosis)
• Ingestions
• Ammonium chloride and Acetazolamide.
• Hyperalimentation fluids (i.e. total parenteral nutrition)
• Some cases of ketoacidosis, particularly during insulin treatment
• Alcohol (such as ethanol) can effect anion gap by inducing alcohol dehydrogenase enzyme.

Low anion gap

A low anion gap is relatively rare but may occur from the presence of abnormal positively charged proteins, as in multiple myeloma, or in the setting of a low serum albumin level.

References

1. ^ Physiology at MCG 7/7ch12/7ch12p51
2. ^ [1]
3. ^ [2]
4. ^ [3] The Fall Of The Serum Anion Gap.

External links

• Clinical Physiology of Acid-Base and Electrolyte Disorders by Rose, Post
• Intensive Care Medicine by Irwin and Rippe
• The ICU Book by Marino
• Calculator at mcw.edu

•  • [ e] Urinary system, physiology: renal physiology and acid base physiology
Filtration	Ultrafiltration - Countercurrent exchange
Hormones affecting filtration	Antidiuretic hormone (ADH) - Aldosterone - Atrial natriuretic peptide
Endocrine	Renin - Erythropoietin (EPO) - Calcitriol (Active vitamin D) - Prostaglandins
Assessing Renal function / Measures of dialysis	Glomerular filtration rate - Creatinine clearance - Renal clearance ratio - Urea reduction ratio - Kt/V - Standardized Kt/V - Hemodialysis product
Acid base physiology	Fluid balance - Darrow Yannet diagram - Body water - Interstitial fluid - Extracellular fluid - Intracellular fluid/Cytosol - Plasma - Transcellular fluid - Base excess - Davenport diagram - Anion gap
Buffering/compensation	Bicarbonate buffering system - Respiratory compensation - Renal compensation

In medicine, differential diagnosis (sometimes abbreviated DDx or ΔΔ) is the systematic method physicians use to identify the disease causing a patient's symptoms.

Before a medical condition can be treated, it must be identified.
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Metabolic acidosis
Classification & external resources

Davenport diagram
ICD-10 E 87.2
ICD-9 276.2

DiseasesDB 92
MedlinePlus 000335
eMedicine emerg/312   med/1458 ped/15

In medicine, metabolic acidosis
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The chloride ion is formed when the element chlorine picks up one electron to form an anion (negatively-charged ion) Cl ⁻ . The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides.
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bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid.

Chemical properties

The bicarbonate ion (hydrogen carbonate) is an anion with the empirical formula HCO₃
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ion is an atom or molecule which has lost or gained one or more electrons, making it positively or negatively charged. A negatively charged ion, which has more electrons in its electron shells than it has protons in its nuclei, is known as an anion
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Sodium (IPA: /ˈsəʊdiəm/) is a chemical element which has the symbol Na (Latin: natrium), atomic number 11, atomic mass 22.9898 g/mol, common oxidation number +1.
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Potassium (IPA: /pə(ʊ)ˈtasiəm/, /pə'tæsiəm/) is a chemical element. It has the symbol K (Arabic: al qalja
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ion is an atom or molecule which has lost or gained one or more electrons, making it positively or negatively charged. A negatively charged ion, which has more electrons in its electron shells than it has protons in its nuclei, is known as an anion
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colorimeter is an instrument for determining the concentration of a particular compound in a preparation by comparing the intensity of colour in it with that of a standard (control) preparation of known concentration. This device used for colorimetry was invented by Jan Szczepanik.
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A ketone (pronounced as key tone) is either the functional group characterized by a carbonyl group (O=C) linked to two other carbon atoms or a chemical compound that contains this functional group.
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Lactic acid (IUPAC systematic name: 2-hydroxypropanoic acid), also known as milk acid, is a chemical compound that plays a role in several biochemical processes.
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Hyperchloremic acidosis
Classification & external resources

ICD-10 E 87.2
ICD-9 276.2

eMedicine med/1071   Hyperchloremic acidosis is a form of metabolic acidosis associated with a normal anion gap, a decrease in plasma bicarbonate
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Lactic acidosis
Classification & external resources

Lactic acid
ICD-10 E 87.2
ICD-9 276.2

DiseasesDB 29145
MedlinePlus 000391
eMedicine med/1253  

MeSH C18.452.076.176.
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Ketoacidosis is a type of metabolic acidosis which is caused by high concentrations of ketone bodies, formed by the deamination of amino acids, and the breakdown of fatty acids.
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Diabetic ketoacidosis (DKA) is a life-threatening complication in patients with untreated diabetes mellitus (chronic high blood sugar or hyperglycemia). Near complete deficiency of insulin and elevated levels of certain stress hormones combine to cause DKA.
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For the song by Starsailor, see .

Alcoholism is a term with multiple and sometimes conflicting definitions. In common and historic usage, alcoholism refers to any condition that results in the continued consumption of alcoholic beverages despite the
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Ethanol, also known as ethyl alcohol, drinking alcohol or grain alcohol, is a flammable, colorless, slightly toxic chemical compound, and is best known as the alcohol found in alcoholic beverages.
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Ethylene glycol (monoethylene glycol (MEG), IUPAC name: ethane-1,2-diol) is an alcohol with two -OH groups (a diol), a chemical compound widely used as an automotive antifreeze.
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Lactic acid (IUPAC systematic name: 2-hydroxypropanoic acid), also known as milk acid, is a chemical compound that plays a role in several biochemical processes.
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Methanol, also known as methyl alcohol, carbinol, wood alcohol, wood naptha or wood spirits, is a chemical compound with chemical formula CH₃OH.
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Paraldehyde is the cyclic form of three acetaldehyde molecules (a trimer). A colourless to pale yellow pungent liquid, it is sparingly soluble in water and highly soluble in alcohol. It has industrial and medical uses. It was first synthesized in 1829 by Wildenbusch.
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Aspirin^®, or acetylsalicylic acid (IPA: /əˌsɛtɨlsælɨˌsɪlɨk ˈæsɨd/
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cyanide ion, CN⁻.
From the top:
1. Valence-bond structure
2. Space-filling model
3. Electrostatic potential surface
4. 'Carbon lone pair' HOMO]] A cyanide
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3, 4, 6
(amphoteric oxide)
Electronegativity 1.83 (Pauling scale)
Ionization energies
(more) 1st: 762.5 kJmol⁻¹
2nd: 1561.9 kJmol⁻¹
3rd: 2957 kJmol⁻¹

Atomic radius 140 pm
Atomic radius (calc.
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Isoniazid is also called isonicotinyl hydrazine or INH. Isoniazid is a first-line antituberculous medication used in the prevention and treatment of tuberculosis. Isoniazid is never used on its own to treat active tuberculosis because resistance quickly develops.
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Methanol, also known as methyl alcohol, carbinol, wood alcohol, wood naptha or wood spirits, is a chemical compound with chemical formula CH₃OH.
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Metformin (INN; trade names Glucophage, Diabex, Diaformin, Fortamet, Riomet, Glumetza, Cidophage and others) is an anti-diabetic drug from the biguanide class of oral antihyperglycemic agents.
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MeSH D014511

Uremia is a term used to loosely describe the illness accompanying kidney failure. In kidney failure, urea and other waste products, which are normally excreted into the urine, are retained in the blood.
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Diabetic ketoacidosis (DKA) is a life-threatening complication in patients with untreated diabetes mellitus (chronic high blood sugar or hyperglycemia). Near complete deficiency of insulin and elevated levels of certain stress hormones combine to cause DKA.
..... Click the link for more information.

Paraldehyde is the cyclic form of three acetaldehyde molecules (a trimer). A colourless to pale yellow pungent liquid, it is sparingly soluble in water and highly soluble in alcohol. It has industrial and medical uses. It was first synthesized in 1829 by Wildenbusch.
..... Click the link for more information.