INTRODUCTION. Determination of the serum anion gap (AG) is primarily used in the differential diagnosis of metabolic acidosis . (See Approach to the adult with metabolic acidosis, section on 'Physiologic interpretation of the serum anion gap'.). However, the serum AG can also become abnormal in other conditions, a finding that may be of diagnostic importance  An increase in serum osmolality and serum osmolal gap with or without high-anion-gap 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 The diagnosis of NAGMA may be made in one of two ways (red arrows above)Patient has normal anion gap with metabolic acidosis (bicarbonate < 22 mM). Patient has an anion gap metabolic acidosis, but the decrease in bicarbonate is much greater than the elevation in anion gap (indicating the combination of an anion-gap metabolic acidosis plus a non-anion-gap metabolic acidosis) The causes of an elevated osmolal gap with and without an accompanying anion gap acidosis are listed in Table 3. The Anion and Osmolal Gap in Toxic Alcohol Ingestion It is important to understand that the parent alcohols are responsible for the majority of the osmolal gap, whereas their organic acid metabolites elevate the anion gap. Figure
Elevated anion gap should be regarded as reflecting a life-threatening abnormality until proven otherwise. In an ill patient, seriously consider whether elevated anion gap may reflect hyperlactatemia and consider initiating the evaluation for hyperlactatemia (even before the lactate level returns) The normal anion gap depends on serum phosphate and serum albumin concentrations An elevated anion gap strongly suggests the presence of a metabolic acidosis The normal anion gap varies with different assays, but is typically 4 to 12mmol/L (if measured by ion selective electrode; 8 to 16 if measured by older technique of flame photometry Low or Negative Serum Anion Gap. A serum anion gap that is below the lower limits of normal is a relatively infrequent occurrence. Its prevalence ranged from 0.8 to 3% of more than 80,000 total sets of electrolytes that were obtained in two large clinical laboratories (18-20).The relatively infrequent occurrence of a low anion gap might reflect, in part, the wide range of the normal serum.
A high anion gap may indicate metabolic acidosis, which requires medical management. The treatment of metabolic acidosis typically requires addressing the underlying cause. Some possible treatments for metabolic acidosis include detoxification if caused by drugs or toxins and insulin if the condition is caused by diabetes [ 9 ] The criteria for diagnosis of diabetic ketoacidosis (DKA) include: Blood glucose >250 mg/dl. Ketonemia or ketonuria (plasma beta0hydroxybutyrate >3 mmol/l or urine ketones ≥3+) pH <7.3 or serum bicarbonate <15 mEq/L. In a patient with diabetes, presence of hyperglycemia and ketosis in the absence of acidosis is consistent with a diagnosis of. The anion gap test tells you how much acid is in your blood. Acid levels that are higher or lower than normal can tip your doctor off to a health problem and help them find the right treatment for.. By contrast, those with CKD (with or without hyporeninemic hypoaldosteronism), certain organic acidoses such as ketoacidosis, toluene intoxication, and d-lactic acidosis, or profuse diarrhea (sufficient to produce hyperproteinemia and hypotension-induced lactic acidosis) can have a nongap acidosis, a high anion gap acidosis, or both (12,25-27.
The diagnosis of EG toxicity is made via a combination of the patient's history, the clinical picture, and a laboratory analysis showing an anion gap metabolic acidosis with an increased osmolal gap. The analysis of the laboratory findings requires consideration of the time of ingestion and the interval between ingestion and presentation to the. High anion gap metabolic acidosis is typically caused by acid produced by the body. More rarely, it may be caused by ingesting methanol or overdosing on aspirin. The Delta Ratio is a formula that can be used to assess elevated anion gap metabolic acidosis and to evaluate whether mixed acid base disorder (metabolic acidosis) is present
However, a lesser increase in the serum anion gap (anion gap 24 mEq/L or less) can be present without an identifiable, accumulating acid in >30% of cases (44). Others also have reported high anion gap forms of metabolic acidosis in which only a portion of the offending acids could be identified (47,48) The anion gap is affected by changes in unmeasured ions. In uncontrolled diabetes, there is an increase in ketoacids due to metabolism of ketones.Raised levels of acid bind to bicarbonate to form carbon dioxide through the Henderson-Hasselbalch equation resulting in metabolic acidosis. In these conditions, bicarbonate concentrations decrease by acting as a buffer against the increased presence. . When bicarbonate is used up to correct the acid-base balance, the gap widens (Kraut and Madias, 2007). Normal anion gap metabolic acidosis is also called hyperchloremic acidosis because the kidneys reabsorb chloride instead of reabsorbing bicarbonate (Emmett and. In theory, therefore, the finding of hypochloremia in conjunction with an anion gap acidosis should evidence a coexisting metabolic alkalosis. In the clinical setting, however, hypochloremia is occasionally found in patients with anion gap acidosis but without exposure to a recognized alkalosis-inducing process
A high anion gap value means that your blood is more acidic than normal. It may indicate that you have acidosis. Conditions that can cause acidosis (and therefore a high anion gap value) include:. This leads to a narrow anion gap, an electrically neutral state without correcting the pathology that induced the acidosis. Likewise, increased Cl may displace bicarbonate intracellularly. To determine the exact etiology of a narrow anion gap, hyperchloremic acidosis requires another test, the urine anion gap. The urine anion gap is calculated. Unusual Causes of Anion Gap Metabolic Acidosis. The MUDPALES acronym, which details the main causes for anion gap metabolic acidosis (Methanol, Uremia, Diabetic ketoacidosis, Paraldehyde, Alcohol, Lactic acidosis, Ethylene glycol, Salicylate toxicity), is one of the most successful medical acronyms of all time. There are a few other.
The Anion Gap calculator evaluates states of metabolic acidosis. The Anion Gap calculator evaluates states of metabolic acidosis. This is an unprecedented time. It is the dedication of healthcare workers that will lead us through this crisis. Thank you for everything you do This means that a metabolic acidosis without an abnormal anion gap is also a hyperchloremic metabolic acidosis 15). A metabolic acidosis without an increased anion gap results from many processes including severe diarrhea, type 1 renal tubular acidosis, long-term use of carbonic anhydrase inhibitors, and suctioning of gastric contents
range in the majority of patients, without the ﬂuctuations seen among patients undergoing MHD . Even though CPD therapy is successful in normalizing the serum CO 2 levels in almost 90% of patients, the anion gap remains wide in over 95% of patients . The magnitude of anion gap in CPD patients is associated with higher serum ure anion gap, due to increased concentrations of the lactate anion.2 When lactic acidosis is caused by bioenergetic failure, excessive endogenous lactate is generated as a without metabolic. Increased serum osmolal gap with or without high-anion-gap metabolic acidosis can be an important clue to toxic alcohol intoxications The presence and magnitude of serum osmolal gap depends on several factors, including molecular weight of the offending alcohol, baseline serum osmolal gap, and state of metabolism of the parent alcoho Ethylene glycol classically produces an elevated anion gap metabolic acidosis. We report a series of patients with ethylene glycol toxicity with a component of non-anion gap metabolic acidosis without known associated confounding factors. A retrospective review of Poison Control Center records were searched more than 8 years (2000-2007) for.
. However, isopropyl alcohol does not cause an elevated anion gap metabolic acidosis (methanol and ethylene glycol poisoning) and is not associated with retinal abnormalities (methanol poisoning) or kidney failure (ethylene glycol poisoning) The causes of high anion gap metabolic acidosis (HAGMA) are well described in the literature. However, sometimes more frequent causes of HAGMA cannot explain its occurrence. In the case of HAGMA and severe neurological depression in the absence of other causes of HAGMA, clinicians should consider an intoxication with gamma-hydroxybutyrate (GHB. Lactic acidosis is a high anion gap metabolic acidosis due to elevated blood lactate. Lactic acidosis results from overproduction of lactate, decreased metabolism of lactate, or both. Type A lactic acidosis, the most serious form, occurs when lactic acid is overproduced in ischemic tissue—as a byproduct of anaerobic generation of adenosine. Metabolic acidosis is primary reduction in bicarbonate (HCO 3 −), typically with compensatory reduction in carbon dioxide partial pressure (P co 2); pH may be markedly low or slightly subnormal.Metabolic acidoses are categorized as high or normal anion gap based on the presence or absence of unmeasured anions in serum Detection of acidosis may be complicated by concurrent metabolic alkalosis due to vomiting, resulting in a relatively normal pH; the main clue is the elevated anion gap. If history does not rule out toxic alcohol ingestion as a cause of the elevated anion gap, serum methanol and ethylene glycol levels should be measured
High anion gap metabolic acidosis made easy using the MUDPILES mnemonic. Learn the anion gap equation to calculate the level and apply it to a metabolic acidosis blood gas analysis. Learn the normal range for an anion gap and the formula that will determine if it is high or low. The MUDPILES acrony Metformin-associated lactic acidosis was characterized by elevated blood lactate levels (>5 mmol/Liter), anion gap acidosis (without evidence of ketonuria or ketonemia), an increased lactate/pyruvate ratio; and metformin plasma levels generally >5 mcg/mL [see Warnings and Precautions (5.1)] # Elevated anion gap - With acidosis MUDPILES - Methanol - Uremia - Diabetic ketoacidosis - Paraldehyde - Iron & Isoniazid - Lactic acidosis - Ethylene glycol - Salicylate - Others (Carbon monoxide, Cyanide, Hydrogen sulfide, Theophylline, Toluene) - Without acidosis - Dehydration - Alkalosis - Sodium salts of unmeasured anions (Citrate, Lactate, Acetate) 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 patient's serum). An anion gap is usually considered to be high if it is over 12 mEq/L. High anion gap metabolic acidosis is caused generally by acid produced by the body, Delta ratio 1: A hyperchloremic or normal anion gap metabolic acidosis is present in addition to a high anion gap metabolic acidosis. Delta ratio 1-2: Only a high anion gap metabolic acidosis is present. Delta ratio > 2: A chronic respiratory acidosis or a metabolic alkalosis is present in addition to a high anion gap metabolic acidosis
The approach to the patient with acute renal failure and elevated anion and osmolal gap is difficult. Differential diagnoses include toxic alcohol ingestion, diabetic or starvation ketoacidosis, or 5-oxoproline acidosis. We present a 76-year-old female with type 2 diabetes mellitus, who was found at home in a confused state. Laboratory analysis revealed serum pH 6.84, bicarbonate 5.8. Causes of High and Low Anion Gap: Normally the anion gap in a person ranges between 3 to 10 (mEq/L). Several conditions can produce imbalance in the pH level of blood resulting in abnormal anion gap. Let us know the reasons of high anion gap first. Causes of high anion gap: High anion gap occurs when the blood is excessively acidic in nature
High Anion Gap. A high anion gap is characterized by a gap of more than 10 to 11 mEq/L. Causes. In a high anion gap, the presence of acidosis causes the bicarbonate ions to decrease. Common conditions that lead to a high anion gap include the following: Lactic acidosis; Ketoacidosis as seen in diabetes and alcoholism; Dehydratio The exact mechanism by which bupropion can cause high anion gap metabolic acidosis is unclear, but this drug is a monocyclic aminoketone - a structure known to cause metabolic acidosis. Conclusions: Bupropion overdose should be considered as a cause of high anion gap metabolic acidosis in the appropriate clinical setting
An anion gap blood test is a way to check the levels of acid in your blood. The test is based on the results of another blood test called an electrolyte panel. Electrolytes are electrically charged minerals that help control the balance of chemicals in your body called acids and bases. Some of these minerals have a positive electric charge Elevated Anion Gap. An increase in an anion gap is most often due to some for of a metabolic acidosis, such as, ketoacidosis, lactic acidosis, acute/chronic kidney disease, toxic alcohol ingestion, and long term acetaminophen use. Less common causes of increased anion gap is due to hyperalbuminemia and/or hyperphosphatemia Abnormal anion gap is a relatively common occurrence among hospitalized patients, with increased anion gap being far more common than reduced anion gap. A retrospective study of 6868 sets of serum electrolytes among hospitalized patients , for example, revealed incidences of increased and reduced anion gap to be 37.6 % and 2.9 %, respectively
The anion gap is the difference between the concentration of sodium and its main anions, chloride and bicarbonate, and normally ranges between 8 and 12 mEq/L. An elevated anion gap indicates that a metabolic acidosis has been caused at least in part by the presence of an acid with an unmeasured anion Anion Gap. Anion Gap = Na+ - (Cl- + HCO3-) An elevated anion gap strongly suggests the presence of a metabolic acidosis. The normal anion gap depends on serum phosphate and serum albumin concentrations. The normal AG = 0.2 x [albumin] (g/L) + 1.5 x [phosphate] (mmol/L) MDCalc Anion Gap Calculator A CKD cat with metabolic acidosis would normally have an increased anion (pronounced an-eye-on) gap. The anion gap is a calculated measurement, being the difference between measured concentrations of cations (pronounced cat-eye-ons) and anions in the blood. It is calculated as follows: AG = [Na+ + K+] - [Cl- + HCO3] which in English means. Calculation of the anion gap which reflects the difference between the positively charged cations and the negatively charged anions in the blood is often a part of this diagnostic work up. An elevated anion gap acidosis is often observed with the ingestion of toxic alcohols or drugs, such as aspirin
The anion gap (AG) without potassium is calculated first and if a metabolic acidosis is present, results in either a high anion gap metabolic acidosis (HAGMA) or a normal anion gap acidosis (NAGMA). A low anion gap is usually an oddity of measurement, rather than a clinical concern Elevated anion gap metabolic acidosis: Bicarbonate reduced through buffering of added strong acid; Anion gap is increased due to retention of the unmeasured anion from the titrated strong acid; Normal anion gap metabolic acidosis due to: Kidneys fail to reabsorb or regenerate bicarbonate; Losses of bicarbonate from GI tract (diarrhea Anion Gap is maintained by near balance of key cations (sNa+) and key anions (sCl-, sHCO3-) In Non-Anion Gap Metabolic Acidosis, only measured cations and anions are affected. In Diarrhea, bicarbonate is lost and compensated by chloride increase. In Anion Gap Metabolic Acidosis, unmeasured anions are increased The morning following, the patient was found to have delirium, hypotension, and a metabolic acidosis with an elevated anion gap (Table 1). ABG revealed a primary metabolic acidosis with an increased anion gap, mixed with metabolic alkalosis with full respiratory compensation. Lactate and β-hydroxybutyrate were not elevated
High anion gap (AG) metabolic acidosis, a common laboratory abnormality encountered in clinical practice, frequently is due to accumulation of organic acids such as lactic acid, keto acids, alcohol metabolites, and reduced kidney function. The cause of high AG metabolic acidosis often is established easily using historical and simple laboratory data group of chronic conditions characterized by hyperchloremic, normal anion gap metabolic acidosis caused by renal tubular dysfunction, in presence of relatively normal glomerular filtration rate 1,2,4,5; RTA consists of the inability of renal tubules to retain bicarbonate (HCO 3-), or to secrete hydrogen ions (H +), or both, in the presence of normal or mildly reduced glomerular filtration rate. Abdominal tenderness without rebound or guarding; Essential Workup. Increased anion gap metabolic acidosis secondary to the presence of ketones: Venous blood gas may be utilized in lieu of arterial; Differentiate from diabetic ketoacidosis (DKA), toxic alcohol ingestion, and other causes of anion gap metabolic acidosis. Increased Anion Gap Metabolic Acidosis In patients with increased anion gap (AG) metabolic acidosis, unmeasured organic anions, such as ketones or lactate, can be metabolized to HCO3- during recovery. If metabolic acidosis is due to lactate from hypovolemia, take appropriate measures—intravascular volume resuscitation using IV fluids—to.
. Although accumulation of lactic acid was clearly the most likely cause, other additional explanations should be considered, including an overdose of certain acids or acid-producing substances , rhabdomyolysis , diabetic ketoacidosis and a raised serum albumin or serum phosphorus  A high osmolal gap associated with increased anion gap acidosis is said to be indicative of toxic alcohol poisoning though this is not at all specific [Salem and Mujais 1992 [ncbi.nlm.nih.gov] These two conditions should be considered when using the osmolal gap to design therapy (for example, hemodialysis) in the setting of anion gap metabolic. Our patient had high anion gap metabolic acidosis without osmolal gap secondary to ethylene glycol poisoning. Clinical history and typical neurological presentation may facilitate the suspicion of acute intoxication, but the definitive diagnosis may be a challenge in an acute and rapidly evolving clinical setting
Increased anion gap without acidosis Dehydration (hypernatremia): Dehydration→ ↑sodium concentration greater than the corresponding changes of chloride or bicarbonate. However, these changes have no effect on the total number of positive and negative ions (electroneutrality is preserved The normal anion gap value is between 8 and 12. An anion gap of greater than 12 is increased. The differential diagnosis for an elevated anion gap metabolic acidosis (simply called anion gap acidosis) differs from the differential diagnosis for an non-elevated anion gap metabolic acidosis (simply called non-anion gap acidosis) Urinary anion gap; Osmolar gap; The anion gap is useful in a couple of ways: Alerting Role: An elevated anion gap (esp if AG > 20 mmol/l) will alert the clinician to the presence of a high anion gap metabolic acidosis. This can be extremely useful in sorting out complicated mixed disorders. Classification Role: It is used to divide metabolic.
This leads to a narrow anion gap, an electrically neutral state without correcting the pathology that induced the acidosis. Likewise, increased Cl may displace bicarbonate intracellularly. To determine the exact etiology of a narrow anion gap, hyperchloremic acidosis requires another test, the urine anion gap ACA is not among the previously identified causes of high anion gap metabolic acidosis. The temporal profile relating anion gap to ACA initiation, hemodialysis treatment, and ACA discontinuation supports causality in this case. The magnitude of increase in the anion gap appears to have been proportional to the dose of ACA
The increased anion gap acidosis seen in ethylene glycol poisoning is in part due to the accumulation of glycolic acid, which some laboratory analyzers misidentify as lactate [34, 37]. Diabetic ketoacidosis may be accompanied by hyperchloremic acidosis at hospital admission or a few hours after admission [ 35 ] They develop an anion gap metabolic acidosis as a result of ketoacidosis and lactic acidosis. They present with the same symptoms of acidosis as do DKA patients, for example, abdominal pain, nausea, and vomiting, but with low. normal, or slightly elevated glucose levels (in contrast to DKA. in which the glucose level usually is markedly elevated) Non-anion gap acidosis, high-anion gap acidosis, or both can be found at all stages of CKD. The acidosis can be associated with muscle wasting, bone disease, hypoalbuminemia, inflammation, progression of CKD, and increased mortality. Administration of base may decrease muscle wasting, improve bone disease, and slow the progression of CKD
. In clinical practice, we usually group the condition of metabolic acidosis into two groups: normal anion gap metabolic acidosis, and elevated anion gap metabolic. An increase in unmeasured anions, as seen in many causes of metabolic acidosis, results in an elevated serum anion gap. We examined the associations between serum anion gap and blood pressure and between serum bicarbonate and blood pressure in the 1999-2000 and 2001-2002 National Health and Nutrition Examination Surveys (NHANES) The causes of metabolic acidosis, both high anion gap and normal anion gap varieties, are shown in Box 2.Although such categorization is useful, some disorders, such as ketoacidosis, can manifest. It is normally ≤ 14 mEq per liter. A high anion gap occurs in certain metabolic acidoses as a result of the replacement of bicarbonate by anions other than chloride. A low or negative anion gap.
. Without an elevated ketones, they are mistakenly labelled as DKA based on high glucose values. Also, even when they are hypervolemic, they are given lots of iv fluids by physicians trying to religiously follow the protocols and guidelines Aug. 8, 2017. Simply put, High Anion Gap Metabolic Acidosis (HAGMA) is a type of metabolic acidosis caused by a high anion gap usually situated above 12 mEq/L. Metabolic acidosis can be categorized as either high or normal anion gap based on the presence or absence of unmeasured anions in serum. In general, it is caused by an accumulation of.
Two cases of High Anion Gap Metabolic Acidosis (HAGMA) due to pyroglutamic acid (5-oxoproline) are described. In both cases the HAGMA developed during an episode of hospital treatment, in conjunction with paracetamol and antibiotic prescription, and the surviving patient made an uneventful recovery after the drugs were withdrawn The increased unmeasured NH 4+ thus increases the measured anion Cl - in the urine, and the net effect is a negative AG, representing a normal response to systemic acidification. Thus, the finding. PRESENTED ON: 10/23/2019 09:45 AM - 10:45 AM. INTRODUCTION: Anion gap metabolic acidosis (AGMA) is a common scenario in critically ill patients. Common causes are often implied by the acronym, MUDPILES (methanol, uremia, diabetic ketoacidosis, paraldehyde, iron overdose, lactic acid, ethylene glycol and salicylate)
Causes of high anion gap and a normal osmolar gap. Abnormally large value of albumin or other negatively charged serum protein (i.e. the expected normal anion gap is higher, and without correction the calculated anion gap appears raised - but there are no extra osmoles, as all the extra proteins do not contribute much to osmolality Increased acid production (normochloremic metabolic acidosis with elevated anion gap) Pathophysiology. In metabolic acidosis with increased acid production, the arterial partial pressure of carbon dioxide (pCO 2) is appropriately decreased because of respiratory compensation.Furthermore, increased acid production leads to a decrease in HCO 3.In patients without appropriately decreased pCO 2. A take-home message of both papers is that for patients with high anion gap metabolic acidosis without evidence of lactic acidosis or ketoacidosis, paracetamol should be considered in the differential diagnosis. If there is a history of chronic paracetamol use, urine or plasma should be submitted for 5-oxoproline estimation
The development of azotemia, anion retention, and acidosis is defined as uremic acidosis, which is not hyperchloremic. The term hyperchloremic acidosis (ie, RTA) refers to a diverse group of tubular disorders, uncoupled from glomerular damage, characterized by impairment of urinary acidification without urea and anion retention Anion gap is calculated as (Na - Cl - Bicarb). Nothing fancy, no corrections for anything (glucose, albumin, potassium, etc.). More discussion of the anion gap in the chapter on diagnosing acid/base problems here. Elevated anion gap is concerning, because many causes of this are immediately life-threatening
The study involved 188 patients during 3 months. The incidence of acidosis was bigger, but 52 (27.6%) presented a high anion gap without hyperlactatemia, 50 (26.6%) showed a high anion gap with hyperlactatemia, 48 (25.5%) a normal anion gap and in 38 (20.2%) there was no metabolic acidosis Pure elevated anion gap followed by mixed (elevated anion gap and hyperchloremia) were the most common in both the diabetic and nondiabetic populations. Nine of the 11 patients with normal bicarbonate had diabetes. Nondiabetic patients had more mixed metabolic acidosis erence range on the work of . Anion gap can be classified as either high, normal or, in rare cases, low. High anion gap: Anion gap is affected by changes in unmeasured ions. A high anion gap indicates acidosis . E.g. In uncontrolled diabetes, the re is an increase in ketoacids due to metabolism of ketones. Ketoacids are unmeasure
Why a normal anion gap is not zero if the body Follows the law of electro-neutrality. Because The Anion Gap is the Gap between the MEASURED and not the total anions and cations. Since our ability to test ions in ABG is limited to Na+, K+ Cl-, HCO3- (at least in past). This leaves a gap representing the number of unmeasured anions and cations HIGH ANION GAP • High anion gap metabolic acidosis is a form of metabolic acidosis characterized by a high anion gap. • An anion gap is usually considered to be high if it is over 12 mEq/L. • The most common cause for high anion gaps are: Lactic Acidosis. Ketoacidosis (diabetic ketoacidosis). 8. LACTIC ACIDOSIS # Elevated anion gap - With acidosis MUDPILES - Methanol - Uremia - Diabetic ketoacidosis - Paraldehyde - Iron & Isoniazid - Lactic acidosis - Ethylene glycol - Salicylate - Others (Carbon monoxide, Cyanide, Hydrogen sulfide, Theophylline, Toluene) - Without acidosis - Dehydration - Alkalosi Patients whose metabolic acidosis persisted for 12 hours had an incidence of ICU complications rates in hyperlactatemia group of 68.8%, increased anion gap of 68.6%, hyperchloremic of 65.8%, and those without acidosis over 12 hours of 59.3% AKA usually presents with an elevated anion gap acidosis and elevated serum lactate concentration. Some patients may have a normal blood pH due to mixed acid-base disorders owing to vomiting and respiratory alkalosis. 10 Patient symptoms include nausea, vomiting, and abdominal pain. In a metabolic acidosis the anion gap is usually either 'Normal' or 'High'. In rare cases it can be 'low', usually due to hypoalbuminaemia. Calculating the Anion Gap. An arterial blood gas (ABG) machine will often give a print out of the anion gap, but it can also be useful to know how it is calculated