The addition of an organic acid anion will automatically reduce the serum bicarbonate level based on a simple acid base interaction. Once one has calculated the anion gap and finds it raised, one is almost obliged to figure out whether those anions have been solely responsible for the acidosis, or whether another non anion gap cause is lurking in the background. Clinical aspects of the anion gap acute care testing. This concept is illustrated in the image to the right. Your body maintains balance by holding onto or releasing carbon dioxide through the lungs acid or bicarbonate through the kidneys base. Determining the serum anion gap is commonly used in the differential diagnosis of metabolic acidosis. Furthermore, the different diagnosis of a metabolic acidosis. The serum anion gap is calculated from the difference between the measured serum cations sodium and anions chloride and bicarbonate. The 5 big lab clues to toxic alcohol poisoning are. It has been my experience that the correct calculation of the anion gap in the face of hyperglycemia is often confusing. If there is significant elevation of the anion gap then this suggests that there is an abundance of unmeasured ion present. Electrolytes are elements and compounds that occur naturally in the body and control important physiological functions. Cations are positive base and anions are negative acid.
Pdf the anion gap in the serum is useful in the interpretation of acidbase. About 50% of patients have an increased anion gap metabolic acidosis due to concomitant ketoacidosis andor an. The negatively charged proteins account for about 10% of plasma anions and make up the majority of the unmeasured anion represented by the anion gap under normal circumstances. When anion gap calculation generates a very small or negative number, an explanation must be sought. This test is most commonly performed in patients who present with altered mental status, unknown exposures, acute renal failure, and acute illnesses. An anion gap blood test is a way to check the levels of acid in your blood. Review the four common causes of high ag acidosis i. 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. Correction of the anion gap for albumin in order to detect. What is the kidney supposed to do to keep acidbase balance.
In this article, learn how an electrolyte test is used to calculate an anion gap, and what low and high anion gap results mean for someones health. When we calculate the anion gap in this patient, we will notice that the anion gap has increased or in other words the unmeasured anions have increased relative to the measured anions. Since the only cation included in the anion gap calculation is sodium, severe hyperkalemia, hypercalcemia, hypermagnesemia or lithium. A high anion gap see the anion gap calculator may be found in clinically ill patients who present soon after acetaminophen ingestion. Note that all these electrolyte levels can be identified through a blood test. The anion gap calculator evaluates states of metabolic acidosis. It is the development of a metabolic acidosis due to a defect in the ability of the renal tubules to either reabsorb bicarbonate or increase hydrogen excretion in response to an acidemia. After initial evaluation, calculate the anion gap every 2 to 4 hours to monitor resolution of acidosis. This assumes that the body is electrochemically neutral, i. The normal value of an anion gap is 8 12 meql if without potassium. The normal anion gap depends on serum phosphate and serum albumin concentrations. Volatile acid co2 and nonvolatile acids, lactate, h2po4, h 2co3 2. For patients with any suspicion for a toxic alcohol ingestion, consider ordering a venous blood gas, calculated anion gap, osmolality, bun, electrolytes and ethanol to calculate an osmolar gap, lactate, ketones and asa level to sort out the anion gap metabolic acidosis and serum calcium. The anion gap is the difference between the number of cations versus anions.
This correction does not apply to the calculation of the anion gap in patients with acidosis and hyperglycemia because the water moving from the intracellular compartment to the extracellular compartment as a result of the hyperglycemia equally dilutes all. The differential diagnosis for an elevated anion gap metabolic acidosis simply called anion gap acidosis differs from the differential diagnosis for an nonelevated anion gap metabolic acidosis simply called non anion gap acidosis. Review of the diagnostic evaluation of normal anion gap metabolic. 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. However, if potassium is given, the normal range value will change to 12 16 meql. This anion gap calculator allows you to compute the ag value and delta gap for the sodium, chloride and bicarbonate values you input in the na cl and hco3 fields. In the advanced mode, you can also input the level of potassium and albumin in blood serum levels, which may sometimes allow correction in the anion gap when taking albumin into account. Calculating the anion gap for patients with acidosis and. Example 6 31 year old aam took too many pills for suicide attempt na 9, k 5. Acidbase and electrolyte teaching case approach to the patient with a negative anion gap michael emmett, md, macp when anion gap calculation generates a very small or negative number, an explanation must be sought. All rtas are characterized by a non anion gap metabolic acidosis.
The serum anion gap is a helpful parameter in the clinical diagnosis of various conditions. Calculated bicarbonate for acidbase disorders american journal. This entity is used in the detection and analysis of acidbase disorders, assessment of quality control in the chemical laboratory, and detection of such disorders as multiple. Calcium, chloride, magnesium, and sodium, among others, are electrolytes. Calculation of the serum anion gap has been used to detect errors in the measurement of serum. Sample question on calculating metabolic acidosis anion gap. Higher anion gap linked to increased mortality kidney news.
The anion gap is a calculation of the unmeasured anions and cations in the blood, based on anions and cations that we can measure sodium, chloride and bicarbonate. The anion of the acid is an unmeasured anion ua and will thus increase the anion gap. Blood plasma is an aqueous water solution containing a plethora of chemical species including some that have a net electrical charge, the result of dissociation of salts and acids in the aqueous medium. You can discover more on the implications of the anion gap below the form. Pdf clinical usefulness of the serum anion gap researchgate. Despite these caveats, calculation of the serum anion gap remains an inexpensive and effective tool that aids detection of various acidbase disorders, hematologic malignancies, and intoxications. Toxic alcohols minding the gaps emergency medicine cases. The serum anion gap, calculated from the electrolytes measured in the chemical laboratory, is defined as the sum of serum chloride and bicarbonate concentrations subtracted from the serum sodium concentration. Calculating the anion gap is critical when assessing a patients acidbase status because an elevated anion gap may alert the physician to the presence of a metabolic acidosis that might not be apparent on first glance of the arterial blood gas values.
Using data on 11,957 adults from the national health and nutrition examination survey 1999 to 2004, the researchers analyzed the relation between the anion gap, as a marker of kidney function, and mortality. Blood ph is described by the hendersonhasselbalch equation 3. A frequently encountered problem in clinical practice is a patient who presents with acidosis and hyperglycemia. Initial evaluation of suspected hyperglycemic hyperosmolar state hhs. Pco2 and calculated values for hco3, tco2, base excess and anion gap art. Do you use potassium in the calculation of anion gap. In the present study, angap was automatically calculated using the above formula. The urine anion gap in context american society of. The anion gap can be readily calculated from routine laboratory data, and although it has its widest application in the diagnosis of various forms of metabolic acidosis,1, 2 it may sometimes provi. An elevated anion gap strongly suggests the presence of a metabolic acidosis. Anion gap metabolic acidosis usmle how to calculate and normal anion gap metabolic acidosis duration. An example would best serve to illustrate the point. It is the dedication of healthcare workers that will lead us through this crisis. The anion gap is a value thats calculated using the results of an electrolyte blood test.
By calculation of the anion gap, metabolic acidosis can be divided into one of two broad categorieselevated anion gap metabolic acidosis and normal anion gap metabolic acidosis. Electrolytes are electrically charged minerals that help control the balance of chemicals in your body called acids and bases. What is the role of an anion gap value in the workup of. A higher serum anion gap early in the course of kidney disease is associated with significantly increased mortality, reports a study in kidney international. Were this a simple one cause acidosis, the acid causing her drop in ph should have lowered her co2 to only about 19 meql. It is indicated for the relieve of fever and pain associated with colds and flu, fever. The test is based on the results of another blood test called an electrolyte panel. In the calculation of results for pco2, concentration is re lat ed to potential through the nernst equation. This anion gap calculator can be used to estimate the anion gap in blood serum, measured in the levels of sodium, chloride, and bicarbonate. 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. This means that it is not directly measured by a specific lab test.