The serum anion gap is calculated from the difference between the measured serum cations sodium and anions chloride and bicarbonate. These anions are not part of the aniongap calculation and there is a secondary loss of hco. Normal anion gap metabolic acidosis is a com mon but often. A generation of clinicians has been taught that the normal anion gap ag is 8 to 16 mmoll. The difference is referred to as the anion gap, because there. Review of the diagnostic evaluation of normal anion gap metabolic. Determining the serum anion gap the sodium concentration minus the sum of the chloride and bicarbonate concentrations is helpful in evaluating patients with metabolic acidosis. The urine anion gap is used for differential diagnosis in metabolic acidosis using measured ions in the urine. Relationship between serum anion gap and diabetes mellitus keywords anion gap, diabetes mellitus, serum anion. Background information the anion gap ag is the difference in concentrations between negativelycharged electrolytes anions and positivelycharged electrolytes cations.
In patients with known anion gap metabolic acidosis, the value of serum bicarbonate hco3 in the dg equation cancels, thus requiring only two serum values. Acidbase balance disturbances lane community college. Metabolic acidosis is primary reduction in bicarbonate hco 3. In contrast, nonmetallic atoms attract electrons more strongly than metallic atoms, and so nonmetals tend to gain electrons and form anions. The anion gap is the measurement in the difference between the cations and the anions in the extracellular space. The test results are done from the results of an electrolyte panel, another blood test. If met acidosis, calculate anion gap to see if high or normal anion gap. Approach to the evaluation of a patient with an increased. For statistical analysis, descriptive and inferential statistics were performed using spearman correlation test and linear correlation with ph and formula stewart. In inorganic acidosis, the anion is chloride and the anion gap does not change. Anion gap gilfix formula and have good correlation with the stewart.
Metallic atoms hold some of their electrons relatively loosely, and as a result, they tend to lose electrons and form cations. To learn what factors can interfere with your anion gap test results, keep reading. This means that it is not directly measured by a specific lab test. Determining the serum anion gap is commonly used in the differential diagnosis of metabolic acidosis. The two most common ways to estimate unmeasured anions are the anion gap ag calculation and the physicochemical approach of the strong ion gap sig.
Although ethylene glycol, methanol, and ethanol ingestions result in anion gap and osmolar gap, isopropyl alcohol results in only an osmolar gap. This helps your healthcare provider diagnose acidbase problems. Anion gap is defined as the difference between measured cations sodium and potassium and anions chloride and bicarbonate in serum. Anion gap corrected for albumin, phosphate and lactate is a good. The serum anion gap has been utilized to identify errors in the measurement of electrolytes, to detect paraproteins, and, most relevant to the nephrologist, to evaluate patients with suspected acidbase disorders. An anion gap is usually considered to be high if it is over 12 meql.
The most common cause of low anion gap yours is only slighly low is low. The plasma anion gap may not change in hyperchloremic metabolic acidosis. Anion gap the most prevalent cation minus the sum of the most prevalent anions bicarbonate may also be referred to as total co 2 or carbon dioxide. Metabolic acidosis can be divided into two categories. The urine anion gap in context american society of. However, the increase in serum osmolal gap and metabolic acidosis can occur either together or alone depending on several factors. The anion gap is a way to differentiate between a metabolic acidosis caused by hco 3loss, or an increase in fixed acids.
The increase in serum osmolar gap is usually less pronounced in ketoacidosis, lactic acidosis, and advanced chronic kidney disease and therefore the serum osmolarity and osmolar gap calculations are usually not done in these populations. The best way to predict units change equation stewart was the base deficit. It is an infrequent form of metabolic acidosis and accounts to only one to three percent of all cases. In patients with hypoalbuminemia, the anion gap should be corrected by adding 2. Clinical chemistry, immunology and laboratory quality control, 2014. When bicarbonate excretion in urine is high, it can contribute significantly to the uag. Modified delta gap equation for quick evaluation of mixed. The plasma anion gap is normally accounted for by proteins and other organic acids in the anionic form, phosphates, and sulfate. Normochloremic metabolic acidosis is usually associated with an increase in the anion gap.
Calculation of the serum anion gap has been used to detect errors in the measurement of serum. An increase in serum osmolality and serum osmolal gap with or without highaniongap metabolic acidosis is an important clue to exposure to one of the toxic alcohols, which include methanol, ethylene glycol, diethylene glycol, propylene glycol, or isopropanol. A read is counted each time someone views a publication summary such as the title, abstract, and list of authors, clicks on a figure, or views or downloads the fulltext. High anion gap metabolic acidosis is caused generally by acid produced by the body.
Under most circumstances, clinicians rely on the serum bicarbonate concentration to evaluate the anion gap and the metabolic component of an acidbase disturbance. This case illustrates how a mixed metabolic acidbase disorder could be evaluated without knowledge of the serum bicarbonate level by using delta gap dg equation. Use winters formula and the other chronicacute resp alkacidosis relationships to figure out if the compensation is appropriate or if there a 2nd acidbase disorder present 3. In organic acidosis, the anion gap increases because bicarbonate decreases, chloride remains constant, and the unmeasured anion lactate, ketone, phosphate increases. Pdf clinical usefulness of the serum anion gap researchgate. The anion gap is an artificial measure, which is calculated by subtracting the total number of anions negatively charged ions bicarbonate and chloride from the total number of cations sodium and potassium. If the anion gap is above the normal value of 812, see your doctor to determine whether you have a condition known as metabolic acidosis.
A normal anion gap is generally considered to be 8 to 12 in a patient with a normal serum albumin concentration of 4. Anion gap definition of anion gap by medical dictionary. There is also a significant osmolar gap of approximately 40. From figure 1 it is ob vious that the elements used in the ag equation are quan.
What kind of anion gap would cause suspicion of anion gap acidosis leading you to search for the most likely cause. By looking at the difference between the measurable cations and ions we can evaluate the cause of a metabolic acidois. This patient has a normal anion gap of 12 with a normal bicarbonate that is consistent with his isopropyl alcohol ingestion. The reason for the later way has become widely accepted, as potassium concentrations, being very low, usually have little effect on the calculated gap. Further experimental data will be necessary to more clearly establish the normal range for the anion gap of animals. Acidosis can disturb many cell functions and should be recognized as quickly as possible, when present. Following a brief overview of the concept of the anion gap there is extensive discussion of the distinction between normal anion gap metabolic acidosis and high anion gap metabolic acidosis. Metabolic acidosis occurs when the body produces too much acid, or when the kidneys are not removing enough acid from the body. This test is most commonly performed in patients who present with altered mental status, unknown exposures, acute renal failure, and acute illnesses. Anion gap is a calculation for classifying metabolic acidosis. In this paper explains in detail the construction, display and interpretation of the different equations. Pdf the anion gap in the serum is useful in the interpretation of acidbase disorders and in the diagnosis of other conditions. Incidence, nature, and etiology of metabolic acidosis in. Respiratory metabolic abgs ph sid hendersonhasselbalch base excess.
It is used to help distinguish between aniongap and nonaniongap metabolic acidosis. Relationship between serum anion gap and diabetes mellitus. Anion gap is the difference between the sum of cations and anions found in plasma or serum. The serum anion gap in the evaluation of acidbase disorders. See approach to the adult with metabolic acidosis, section on physiologic interpretation of the serum anion gap. Hypoproteinemia causes a decrease in the anion gap. Metabolic acidosis endocrine and metabolic disorders. Madias, in comprehensive clinical nephrology fourth edition, 2010.
Anion gap is subdivided into levels depending on the symptoms and cause. Determination of the serum anion gap ag is an important step in the differential diagnosis of acidbase disorders and especially metabolic acidosis 15. It should be used in the context of evaluating someone who presents with a low level of plasma bicarbonate caused by either metabolic acidosis or chronic. The anion gap is used to aid in the differential diagnosis of metabolic acidosis.
The serum ag is calculated from the following formula, which. This formula can be used if there is a value for potassium. Learn vocabulary, terms, and more with flashcards, games, and other study tools. This test looks at electrically charged particles in your blood. As in the calculation of plasma anion gap, bicarbonate should be a part of the uag calculation formula 1. Anion gap serum description the anion gap is a value calculated using the results of an electrolyte profile. The uag, like the plasma anion gap, serves mainly to identify an abnormal ion suspected to be either present in excessive quantities or inappropriately low for a given clinical setting. High anion gap metabolic acidosis is a form of metabolic acidosis characterized by a high anion gap a medical value based on the concentrations of ions in a patients serum. The anion gap ag or agap is a value calculated from the results of multiple individual. Metabolic acidoses are categorized as high or normal anion gap based on. Engelking, in textbook of veterinary physiological chemistry third edition, 2015. Confirm that an acidosis is indeed metabolic narrow down the cause of a metabolic acidosis monitor the progress of treatment in a metabolic acidosis the anion gap is usually either normal or high.
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