What Is An Anion Gap Blood Test Used For
The anion gap reveals whether your blood has an imbalance of electrolytes or if your blood is too acidic or too basic. If you have too much acid in your blood, its called acidosis. If your blood is too basic, you may have a condition called alkalosis.
One common application of the anion gap is classifying cases of metabolic acidosis , which is a potentially life-threatening condition that requires medical treatment.
What Does It Mean If Your Anion Gap Result Is Too High
An anion gap level of 20 or above signals a problem. The most likely issue is acidosistoo much acid in the blood. Acidosis can start in the kidneys or the lungs.
Metabolic Acidosis occurs when the kidneys cant eliminate enough acid, or they are eliminating too much base. Poorly controlled diabetes can result in metabolic acidosis, as well as a lack of sodium in the body and an excess of lactic acid. A lack of sodium typically indicates diarrhea and / or vomiting. However, lactic acid buildup can be caused by chronic alcohol use, heart failure, cancer, seizures, liver failure, and prolonged exercise. Symptoms of metabolic acidosis:
– Rapid, shallow breathing
– Jaundice
– Increased heart rate
– Breath that smells fruity
Respiratory acidosis happens when there is too much CO2 in the body, because the lungs arent working properly. Respiratory acidosis almost always results from a problem with the chest cavities of our bodies. These can include: injury to the chest, difficulty breathing caused by obesity, chronic airway conditions like asthma, muscle weakness in the chest, deformed chest structure, or overuse of alcohol.
What Is The Normal Ph Level Of Blood
In chemistry, pH is a scale that describes how acidic or basic a water solution is. A pH level of 7.0 is neutral and represents the middle of the scale. Acidic solutions have a pH value lower than 7, and basic or alkaline solutions have a pH level higher than 7.
Blood, which is over 90% water, is normally slightly basic, with a normal pH range of about 7.35 to 7.45. Usually, your body maintains the pH of your blood close to 7.4. Your blood’s pH balance is critical to your health, and there are several ways in which your body resists change to your bloods pH. When the balance is off, even by a small amount, it can make you sick.
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When Should I Get An Electrolyte Panel And Anion Gap

Your doctor will decide whether you need an electrolyte panel and anion gap. In many cases, these measurements will be included if you have a test like a basic metabolic panel or comprehensive metabolic panel.
Your doctor may recommend electrolyte testing if you have signs of a condition that could be related to an electrolyte imbalance. Examples of symptoms that may prompt electrolyte testing include:
- Weakness or fatigue
- Muscle twitching, cramps, or paralysis
- Nausea and/or vomiting
If you have already been diagnosed with an electrolyte disorder, your doctor may prescribe an electrolyte panel and anion gap in order to see if your condition has improved, worsened, or stayed the same.
In some cases, a doctor may measure your electrolytes even if you do not have any symptoms. This may occur as part of blood work during a regular health checkup however, professional medical organizations generally do not recommend electrolyte testing in people without symptoms.
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How The Test Is Done
You’ll go to your doctor’s office to get a blood test. Before your appointment, your doctor will tell you if you need to avoid food and certain drinks. Let them know if you’re taking any medicines — especially an antibiotic — because that can affect your test results.
Your doctor will use a needle to take some blood from a vein in your arm. They’ll send the blood sample to a lab for testing. You may have a bit of pain, soreness, or bruising in the area afterward.
What Does Anion Gap Mean In A Blood Test
In blood test results, anion gap is a measurement to check for the acid-base balance of your blood and/or an electrolyte imbalance in your blood. The anion gap is a calculation of the difference between the amounts of some negatively charged electrolytes and the amount of positively charged electrolytes in your blood.
The anion gap measurement is based on the results of individual electrolyte blood tests, which are commonly included in the following routine bloodwork panels:
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Who Performs An Anion Gap Blood Test
A healthcare provider called a phlebotomist usually performs blood draws, including those for an anion gap blood test, but any healthcare provider who is trained in drawing blood can perform this task. A provider then sends the sample to a lab where a medical laboratory scientist prepares the sample and performs the test on machines known as analyzers.
Use Of The Delta Plasma Anion Gap/delta Plasma Hco3
The relationship between the rise in the Panion gap and the fall in the Phco3 is used to detect the presence of coexisting metabolic alkalosis or the presence of both an acid overproduction type and an NaHCO3 loss type of metabolic acidosis .
Another pitfall in the use of the delta Panion gap/delta Phco3 is the failure to correct for the net negative valence attributable to PAlb. When calculating the Panion gap, one must adjust the base value for changes in the charge on the most abundant unmeasured anion in plasma, which is albumin. We emphasize that adjustments should be made for a decrease or an increase in PAlb.
John G. Toffaletti PhD, Craig R. Rackley MD, in, 2022
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Treating Low Anion Gap
Having low anion gap value is a rare condition. In case, the tests have confirmed for low anion gap value, your doctor will prescribe with several other criteria. This will help in the diagnosis of the underlying factor and thereby fix low anion gap with the right treatment. In case, it is found that the cause of your lower anion gap is due to medications with ingredients like bromide or lithium, adjustment of dosages will be prescribed.
What Should I Expect During My Blood Test
Laboratory scientists calculate the anion gap from the results of an electrolyte panel or a comprehensive metabolic panel , which are blood tests.
You can expect to experience the following during a blood test, or blood draw:
- Youll sit in a chair, and a healthcare provider will check your arms for an easily accessible vein. This is usually in the inner part of your arm on the other side of your elbow.
- Once theyve located a vein, theyll clean and disinfect the area.
- Theyll then insert a small needle into your vein to take a blood sample. This may feel like a small pinch.
- After they insert the needle, a small amount of blood will collect in a test tube.
- Once they have enough blood to test, theyll remove the needle and hold a cotton ball or gauze on the site to stop the bleeding.
- Theyll place a bandage over the site, and youll be finished.
The entire procedure usually takes less than five minutes.
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Narrow Anion Gap Metabolic Acidosis
If the acidosis involves a normal anion gap, there is a loss of bicarbonate rather than an increased amount of hydrogen ions, with a concomitant increase in chloride ions. To keep a physiological neutral state, chloride ions migrate out of the cells and into the extracellular space. This causes the patients serum chloride to increase and keeps the anion gap at a normal level 14). 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. When a patient has a narrow ion gap hyperchloremic acidosis, the doctor can calculate the urine anion gap to help determine etiology.
Why Do You Need To Undertake The Agap Blood Test

AGAP is the abbreviation for the term Anion Gap. It is the measurement of the ions present in your blood with either positive or negative charges. Whenever there is an excessive acid found in your blood, there is an increase in the Anion Gap. The presence of high acid in the blood is due to the unsuccessful elimination of acid through your kidneys and lungs. It is essential to undertake the AGAP blood test to monitor the level of acid in the blood.
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Is There Anything Else I Need To Know About An Anion Gap Blood Test
The anion gap blood test provides information about the acid-base balance of your blood. This tells you about the health of many of your body functions. But there is a wide range of normal results and many possible causes of abnormal results. So, talk with your provider about what your test results mean and whether you need additional testing to make a diagnosis.
When Is It Ordered
An electrolyte panel may be ordered as part of a routine health exam, as recommended by your healthcare practitioner. It may also be ordered as a diagnostic aid when you have signs and symptoms, such as:
It is frequently ordered as part of an evaluation when you have an acute or chronic illness and at regular intervals when you have a disease or condition or is taking a medication that can cause an electrolyte imbalance. Electrolyte tests are commonly ordered at regular intervals to monitor treatment of certain conditions, including high blood pressure , heart failure, lung diseases, liver disease and kidney disease.
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Determinants Of The Serum Anion Gap
Although the anion gap can be calculated using serum or plasma electrolytes, most frequently serum values are used. Therefore, our discussion is restricted to the serum anion gap, with the understanding that the anion gap that is calculated using either serum or plasma values is acceptable.
Gamble , in his short lecture syllabus Chemical Anatomy, Physiology, and Pathology of the Extracellular Fluid, was one of the first individuals to emphasize the importance of charge balance in the evaluation of perturbations in the ionic environment of the blood and other body fluids. A graphic display of the ionic environment of the serum, often termed a gamblegram, is depicted in and illustrates the concept that total serum cations and total serum anions must always remain equal to ensure charge balance. Therefore, the sum of circulating cationssodium, potassium, calcium, magnesium, and cationic proteinsmust equal the sum of circulating anionschloride, bicarbonate, anionic proteins, inorganic phosphate, sulfate, and organic anions:
Figure 1.
Ionic environment of the blood depicted to emphasize the need for charge balance. Often referred to as a gamblegram on the basis of the work of James L. Gamble, the total circulating cations and total circulating anions are shown. At all times, the sum of both entities must be equal. This equivalency remains the foundation of the derivation of the serum anion gap.
Rearranging the equation, we obtain:
What Do The Results Mean
Several types of medical conditions can cause abnormal anion gap test results. Your provider will use the results of the anion gap test, your medical history, and other tests to make a diagnosis.
A high anion gap test result may mean that you may have acidosis . Acidosis may be caused by:
- Certain medicines and poisons
A low anion gap test result may mean you have alkalosis . But this result is so rare that your provider will usually have you tested again to make sure the results are accurate.
The most common cause of a low anion gap is a low level of albumin, a protein in the blood. Low albumin may be a sign of not eating enough protein, kidney problems, liver disease, heart disease, or some types of cancer.
Learn more about laboratory tests, reference ranges, and understanding results.
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Urine Anion Gap Formula
The following is the equation for urine anion gap where Na is sodium, K is potassium, and Cl is chloride:
Urine anion gap = Urine Na + Urine K Urine Cl
A positive urine anion gap value is indicative of renal bicarbonate loss, such as renal tubular acidosis. Negative values are found with non-renal bicarbonate losses, such as diarrhea 6).
The urine anion gap provides an estimate of urinary ammonium excretion 7). The normal renal response to metabolic acidosis is to increase acidic ammonium excretion renally. Therefore, a positive urine anion gap between 20 and 90 mEq/L is indicative of low or normal NH4 excretion, such as is seen in distal renal tubular acidosis. A negative urine anion gap between -20 and -50 mEq/L is indicative of increased ammonium excretion. This occurs in patients with metabolic acidosis generated by profuse watery diarrhea. A urine anion gap approaching 0 is indeterminate.
How Do I Prepare For An Anion Gap Blood Test
If youre experiencing symptoms of having a blood pH imbalance, such as shortness of breath or vomiting, your provider will likely have you undergo blood tests as soon as possible. Theres nothing you need to do to prepare in this case.
An anion gap can also be measured from blood test results from a routine comprehensive metabolic panel . If youre undergoing a blood draw for a CMP, you may need to not eat or drink for several hours before your blood draw. In any case, your healthcare provider will let you know if you need to follow any special instructions.
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Will There Be Any Genre Of Preparation Required For The Test
Perhaps the best part about this blood test is that you dont need to take any special preparations, unlike the other blood tests. But, in case, you are allergic to latex, you must inform the doctor. Furthermore, if you are under any medication, it must be given prior intimation as well. This process is mainly conducted so that there are no interferences with the test results.
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What Does The Test Measure

The electrolyte panel measures the blood levels of sodium, potassium, chloride, and bicarbonate.
- Sodium: Sodium is a positively charged electrolyte and plays a vital role in regulating the amount of fluid in the body. It also facilitates normal nerve and muscle activity.
- Potassium: Potassium is positively charged and is important for many functions of cells, muscles, and nerves.
- Chloride: Chloride is negatively charged and works with other electrolytes to control fluid levels and the acid-base balance in the body.
- Bicarbonate: Bicarbonate is a negatively charged electrolyte. In addition to helping to regulate acid-base balance, bicarbonate transports carbon dioxide in the blood. Bicarbonate levels may also be referred to as carbon dioxide levels.
The anion gap is not a test itself instead, it is a mathematical calculation based on electrolyte measurements. It compares the levels of positively and negatively charged electrolytes, which can provide information about the bodys acid-base balance.
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What The Test Measures
The lab will take a close look at electrically charged minerals in your blood called electrolytes. These help keep your blood from becoming too acidic — or not acidic enough.
Electrolytes can carry a positive or negative charge. The anion gap test measures how balanced these charges are. The result is a number that can help your doctor figure out if you have a condition that’s throwing off your acid levels.
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 . The relatively infrequent occurrence of a low anion gap might reflect, in part, the wide range of the normal serum anion gap. As noted previously, factors that cause a reduction in its value might not be sufficient to cause it to fall outside the normal range. Indeed, in one study, approximately 80% of the low values were < 4 mEq/L below the lower limits of normal . A negative serum anion gap is even more uncommon: 0.12% of all sets of electrolytes that were obtained during a 12-mo period in a large clinical laboratory . Disorders that are associated with a low or negative serum anion gap are listed in .
Table 3.
Serum anion gap in metabolic acidoses associated with overproduction or decreased excretion of protons and anions
Ratio of Change in Unmeasured Anion Concentration and Change in Serum Bicarbonate Concentration in Differential Diagnosis of Metabolic Acidosis.
l-Lactic Acidosis .
d-Lactic Acidosis.
The AG/HCO3 in d-lactic acidosis in many studies has been found to be more variable than in l-lactic acidosis . Consistent with this variability, various types of metabolic acidosis can be found, including high anion gap, mixed high anion gap, and normal anion gap acidosis, or normal anion gap acidosis alone .
Ketoacidosis.
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