The most common mechanisms leading to this acidbase disorder include loss of large quantities of base secondary to diarrhea and administration of large quantities of chloridecontaining solutions in the treatment of hypovolemia and various shock states. Chemistry participant reports college of american pathologists. The anion gap is affected by changes in unmeasured ions. Metabolic acidosis refers to any process that increases the hydrogen ions in the body and reduces the bicarbonate concentration. It had been shown that lower bicarbonate and higher anion gap are independently associated with insulin resistance. The anion gap, is really not a gap at all, it just represents the anions we dont usually measure. Metabolic acidosis is subdivided based on presence of anion gap ag, and ag metabolic acidosis is most often due to ketoacidosis, lactic. It may be reported with the results of an electrolyte panel, which is often performed as part of a comprehensive metabolic panel.
Acidbase balance disturbances lane community college. The quantity of hco 3 returned to the blood by this mechanism is fixed by the urine ph level achieved lowest ph achievable is 4. The anion gap in this patient was high and more unmeasured anions were available in the bloodstream than under normal. Mar 31, 2006 the serum anion gap is a helpful parameter in the clinical diagnosis of various conditions.
This underscores the principal clinical utility of the anion gap, which is the evaluation of patients suffering disturbance of acidbase balance. Recent advances have led to a new mnemonic gold mark to differentiate the various causes of anion gap metabolic acidosis. The serum anion gap is a common tool used in clinical practice. Evaluation of factors leading to anion gap reopening in. The urine anion gap is an artificial and calculated measure that is representative of the unmeasured ions in urine. A nonanion gap pattern is commonly found in patients with both acute and chronic metabolic acidosis. Metabolic acidosis caused by concomitant use of paracetamol.
Abnormal anion gap is a relatively common occurrence among hospitalized patients, with increased anion gap being far more common than reduced anion gap. Adverse effects of acute metabolic acidosis primarily include decreased cardiac output, arterial dilatation. Acute nonanion gap metabolic acidosis, also termed hyperchloremic acidosis, is frequently detected in seriously ill patients. Some labs use a wider reference range for anion gap. Functional chemscreen and cbc results tracking form standard. A recent article in ajkd by vichot and rastegar discusses the use of anion gap in metabolic acidosis. The serum anion gap is a helpful parameter in the clinical diagnosis of various conditions.
The anion gap ag or agap is a value calculated from the results of multiple individual medical lab tests. The anion gap and routine serum protein measurements in monoclonal gammopathies. The urine anion gap is a different measure, principally used to determine whether the kidneys are capable of appropriately acidifying urine. As for the ldl and cholesterol, labs use different reference ranges. Acidbase disturbances can result from kidney or nonkidney disorders. The plasma anion gap is normally accounted for by proteins and other organic acids in the anionic form, phosphates, and sulfate. Anion gap is a calculation for classifying metabolic acidosis. It is used to aid in the differential diagnosis of metabolic acidosis the term anion gap without qualification usually implies serum anion gap. Mar 23, 2010 the causes of metabolic acidosis, both high anion gap and normal anion gap varieties, are shown in box 2. Anion gap definition of anion gap by medical dictionary.
Blood ph is described by the hendersonhasselbalch equation 3. Nov 29, 2009 the anion gap is a reflection of your acid base balance in your body, and it is normal. The serum anion gap and the change in anion gap from its baseline. In patients with hypoalbuminemia, the anion gap should be corrected by adding 2.
Nov 07, 2017 the anion gap value is reported in units of milliequivalents per liter meql. Normal results generally fall between 3 and 10 meql. Anion gap 7 12 uric acid 208 351 male 178 327 female total protein 69 74 albumin 40 50 calcium 2. A complete clinical history and physical examination are critical initial steps to begin the evaluation process, followed by measuring serum electrolytes with a focus on potassium level, blood gas, urine ph. Treatment of acute nonanion gap metabolic acidosis. The commonest application of the anion gap is to classify cases of metabolic acidosis into those that do and those that do not have unmeasured anions in the plasma table 1. The anion gap clarifies whether the metabolic acidosis is caused by the accumulation of fixed acids or loss of hco 3. Nov 15, 2019 the urine anion gap is either positive or negative and can be used when the causes of normal anion gap acidosis are unclear. In 1047 hospitalized patients the mean was 12 meqliter, 86 faster volunteers had a mean of meqliter with a.
The causes of metabolic acidosis, both high anion gap and normal anion gap varieties, are shown in box 2. Unmeasured anion during severe sepsis with metabolic acidosis. In inorganic acidosis, the anion is chloride and the anion gap does not change. Engelking, in textbook of veterinary physiological chemistry third edition, 2015. However, with newer electrolyte analyzers, the upper limit of normal has decreased to 1112 mm. Anion gap acidoses have a very different differential diagnosis than nongap acidoses. Anion gap acidoses have a very different differential diagnosis than non gap acidoses. The anion gap is the measurement in the difference between the cations and the anions in the extracellular space. The latter is dependent on the filtered load of phosphate and the fractional reabsorption of phosphate by the renal tubules.
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. Aug 25, 2014 the serum anion gap is a common tool used in clinical practice. Raised levels of acid bind to bicarbonate to form carbon dioxide through the hendersonhasselbalch equation resulting in metabolic acidosis. Is most often due to increased serum lactate or acetoacetate. The urine anion gap is calculated using measured ions found in the urine. It is the dedication of healthcare workers that will lead us through this crisis. Although such categorization is useful, some disorders, such as ketoacidosis, can manifest. The cause of metabolic acidosis kidney international. Hypoproteinemia causes a decrease in the anion gap. Because the anion gap is useful in classifying acidbase disorders, quantitative information on this variable should be readily available. The anion gap value is reported in units of milliequivalents per liter meql. Reference range, interpretation, collection and panels. Microsoft word chem screen tracking form us doctors choice 2010. Laboratory abnormalities include low ph, increased anion gap, and elevated blood lactate.
Nonanion gap metabolic acidosis can present as a form of either acute or chronic metabolic acidosis. So if the anion gap is changed, its because the unmeasured anions have changed. The ag represents anions such as proteins, phosphates, sulfates and organic anions. Diagnosis of metabolic acidbase disorders emcrit project. A retrospective study of 6868 sets of serum electrolytes among hospitalized patients 3, for example, revealed incidences of increased and reduced anion gap to be 37. A positive urine anion gap is seen in conditions of type 1 and type 2 renal tubular acidosis versus almost every other cause of normal anion gap acidosis diarrhea. Metabolic acidosis occurs when the body produces too much acid, or when the kidneys are not removing enough acid from the body. Diagnostic importance of an increased serum anion gap. Every one gram decrease in albumin will decrease anion gap by 2. Handbook of diagnostic biochemistry and hematology in normal pregnancy. Acidbase balance and the anion gap bloomington campus.
The population included all adult patients admitted to a large academic medical center from december 2014 to november 2015 from the emergency department to an adult inpatient floor with a primary diagnosis of. Adverse effects of acute metabolic acidosis primarily include. Metabolic acidosis can be divided into two categories. The following questions will test your knowledge on this very important topic in nephrology. In uncontrolled diabetes, there is an increase in ketoacids due to metabolism of ketones. Between 19% and 41% of patients in intensive care units with acute metabolic acidosis and 20%55% of individuals with chronic uremic acidosis have a nongap pattern 3,4. Clinical chemistry, immunology and laboratory quality control, 2014. When fixed acids accumulate, the anion gap increases, resulting in the following chain of events. Normochloremic metabolic acidosis is usually associated with an increase in the anion gap. This test is most commonly performed in patients who present with altered mental status, unknown exposures, acute renal failure, and acute illnesses.
Metabolic acidosis is subdivided based on presence of anion gap ag, and ag metabolic acidosis is most often due to ketoacidosis, lactic acidosis, renal failure, or toxic ingestions. A raised anion gap means that you are measuring a higher concentration of cations than anions. We identify a mechanism for nonsynaptic, nonvesicular release of adenosine triphosphate atp from axons through volumeactivated anion channels vaacs activated by microscopic axon swelling during action potential firing. The release of neuronal messengers outside synapses has broad biological implications, particularly with regard to communication between axons and glia. A normal anion gap is generally considered to be 8 to 12 in a patient with a normal serum albumin concentration of 4.
We report an unusual case of high anion gap ag metabolic acidosis in a 50yearold woman after longterm ingestion of acetaminophen in combination with hydrocodone vicodin. Acidbase balance and the anion gap iu school of medicine. Historically, the normal range of anion gap was often quoted as being higher e. A complete clinical history and physical examination are critical initial steps to. Albumin is the major unmeasured anion and contributes almost the whole of the value of the anion gap. As for the ag ration, this is a reflection of the protein levels in the body, and it is normal. Relationship between serum anion gap and diabetes mellitus. It may be reported with the results of an electrolyte panel, which is often performed as part of a comprehensive metabolic panel the anion gap is the difference between certain measured cations positively charged ions and the measured anions negatively charged ions in serum, plasma.
Anion gap is defined as the difference between measured cations sodium and potassium and anions chloride and bicarbonate in serum. This pattern can originate from a number of pathophysiologic mechanisms. The anion gap calculator evaluates states of metabolic acidosis. The following questions will test your knowledge on this.
In organic acidosis, the anion gap increases because bicarbonate decreases, chloride remains constant, and the unmeasured anion lactate, ketone, phosphate increases. Volatile acid co2 and nonvolatile acids, lactate, h2po4, h 2co3 2. Differential diagnosis of nongap metabolic acidosis. If the baseline serum anion gap of an individual is not known and the range of normal values of a particular laboratory is used to assess the anion gap, then it is possible that disorders that cause deviations in the serum anion gap might not be recognized because. Metabolic acidosis is a disorder frequently encountered in emergency medicine and intensive care medicine.