Aspartate Aminotransferase

General

Core Lab Study

Synonym/Acronym:
AST.

Rationale
AST is an indicator of cellular damage in liver disease.

A small group of studies in this manual have been identified as Core Lab Studies. The designation is meant to assist the reader in sorting the basic “always need to know” laboratory studies from the hundreds of other valuable studies found in the manual—a way to begin putting it all together.

Normal, abnormal, or various combinations of core lab study results can indicate that all is well, reveal a problem that requires further investigation with additional testing, signal a positive response to treatment, or suggest that the health status is as expected for the associated situation and time frame.

AST is included in the liver function test panel (LFTs) and in the comprehensive metabolic panel (CMP). LFTs are used to identify liver disease, assess severity of injury, or monitor disease process and response to treatment. CMPs are used as a general health screen to identify or monitor conditions such as bone disease, diabetes, hypertension, kidney disease, liver disease, or malnutrition.

Patient Preparation
There are no food, fluid, activity, or medication restrictions unless by medical direction.

Normal Findings
Method: Spectrophotometry, enzymatic.

AgeConventional and SI UnitsSI Units Expressed as microkat/L = (Units/L × 0.017)
Newborn25–75 units/L0.43–1.28 microkat/L
10 days–3 yr15–60 units/L0.26–1.02 microkat/L
Child20–39 units/L0.34–0.66 microkat/L
Adult–older adult
  Male20–40 units/L0.34–0.68 microkat/L
  Female15–30 units/L0.26–0.51 microkat/L
AST levels are very elevated at birth, decrease with age to adulthood, and increase slightly in older adults. Values may be slightly elevated in older adults due to the effects of medications and the presence of multiple chronic or acute diseases with or without muted symptoms.

Critical Findings and Potential Interventions
N/A

Overview

(Study type: Blood collected in a gold-, red-, or red/gray-top tube; related body system: Circulatory and Digestive systems.)

Aspartate aminotransferase (AST) is an enzyme that catalyzes the reversible transfer of an amino group between aspartate and alpha-ketoglutaric acid in the citric acid or Krebs cycle, a powerful and essential biochemical pathway for releasing stored energy. Serum AST rises when there is damage to the tissues and cells where the enzyme is found, and levels directly reflect the extent of damage.

The largest amounts of AST are found in the liver and heart. AST is no longer used as a primary cardiac marker, having been replaced by CK-MB and the more sensitive and specific troponins. Elevations of AST may also be seen in other conditions related to the presence of smaller but significant amounts of AST in the kidneys, pancreas, RBCs, and skeletal muscle.

Examples of Possible Patterns Between AST Levels and Other Core LFT Levels in Specific Hepatic Conditions
DiagnosisAST Level (Other Core LFTs)
Cholestasis↑ Normal to Mild (Alb ↓, ALP ↑↑↑, ALT ↑, TBil ↑)
Cirrhosis↑↑↑ Marked (Alb ↓, ALP ↑ to ↑↑, ALT ↑↑, TBil ↑)
Hepatitis, viral, acute↑↑↑ Marked (Alb ↓, ALP ↑ to ↑↑, ALT ↑↑↑, TBil ↑ to ↑↑)
Hepatitis, toxin or drug related↑↑↑ Marked (Alb ↓, ALP ↑ to ↑↑, ALT ↑↑↑, TBil ↑↑)
Infarction, acute necrosis of the liver, or cancer↑↑ to ↑↑↑ Moderate to Marked (Alb ↓, ALP ↑ to ↑↑, ALT ↑↑↑, TBil ↑↑)
Jaundice, hepatic origin↑↑ Mild to Moderate increase (Alb ↓, ALP ↑ to ↑↑, ALT ↑↑ with ALT rising before AST and TBil, TBil ↑ to ↑↑)
N=Normal, ↓ Normal to Mild decrease, ↑ Normal to Mild increase, ↑ to ↑↑ Normal to Mild or Moderate, ↑↑ Mild to Moderate, ↑↑↑ Marked. Study levels will vary with degree and progression of liver damage. ALT levels remain elevated longer than AST levels.

Indications

  • Assist in the diagnosis of liver disease.
  • Monitor response to therapy with potentially hepatotoxic or nephrotoxic drugs.
  • Monitor response to treatment for various disorders of hepatic function in which AST may be elevated, with tissue repair indicated by declining levels.

Interfering Factors


Factors that may alter the results of the study

  • Drugs and other substances that may increase AST levels include acarbose, ACE inhibitors, acetaminophen (toxic), acetylsalicylic acid, allopurinol, amoxicillin, amiodarone, ampicillin, amytriptyline, ARBs, asparaginase, azathioprine, beta-blockers, baclofen, bupropion, carbamazepine, cephalosporins, chloramphenicol, chlordiazepoxide, chlorpromazine, chlorpropamide, clindamycin, cloxacillin, clopidogrel, codeine, cyproheptadine, cytarabine, danazol, desipramine, dicumarol, doxepin, enflurane, erythromycin, estrogens, ethambutol, ethionamide, ethotoin, ethyl alcohol, fibrates, gentamicin, gold salts, imipramine, isoniazid, ketoconazole, low-molecular-weight heparin, methyl dopa, metaxalone, methotrexate, nafcillin, naladixic acid, nitrofurans, nortriptyline, NSAIDs, omeprazole, oral contraceptives, oxacillin, phenobarbital, phenytoin, probenecid, procainamide, propoxyphene, pyrazinamide, quinidine, rifampin, risperidone, sulfonamides, terbinafine, tetracyclines, trazadone, trimethoprim, valproic acid, verapamil, and zidovudine.
  • Hemolyzed specimens may cause falsely elevated results.
  • Hemodialysis decreases AST values.

Potential Medical Diagnosis: Clinical Significance of Results

Increased in

AST is released from any damaged cell in which it is stored, so conditions that affect the liver, kidneys, heart, pancreas, RBCs, or skeletal muscle and cause cellular destruction demonstrate elevated AST levels.

  • Angina pectoris (acute)
  • Biliary tract obstruction
  • Burns (severe, second/third degree)
  • Cardiac dysrhythmias
  • Cardiac catheterization, angioplasty, or surgery
  • Cirrhosis
  • Exercise (vigorous)
  • Heart failure
  • HELLP syndrome of pregnancy; variant of pre-eclampsia (hemolysis, elevated liver enzymes, low platelet count)
  • Hemolytic anemias
  • Hepatic cancer
  • Hepatic infarction or necrosis (acute, initial)
  • Hepatitis (drug or toxin induced)
  • Hepatitis, viral (acute or reactivation)
  • Infectious mononucleosis
  • Infarction (kidney, liver)
  • Muscle diseases (e.g., dermatomyositis, dystrophy, gangrene, polymyositis, trichinosis)
  • Myocardial infarction (acute)
  • Pancreatitis (acute)
  • Reye syndrome
  • Substance use disorder (alcohol)
  • Trauma (related to injury or surgery of intestines or liver and other sites where AST is found)

Decreased in

  • Hemodialysis (presumed to be related to a corresponding deficiency of vitamin B6 observed in hemodialysis patients)
  • Pregnancy (related to increased demand)
  • Uremia (related to a buildup of toxins that modify the activity of coenzymes required for transaminase activity)
  • Vitamin B6 deficiency (e.g., beriberi, malnutrition) (related to the lack of vitamin B6, a required cofactor for the transaminases)

Nursing Implications, Nursing Process, Clinical Judgement

Potential Nursing Problems Assessment and Nursing Diagnosis

ProblemsSigns and Symptoms
Activity (intolerance related to fatigue, malnutrition, generalized weakness, energy loss)Complaints of excessive fatigue and weakness; inability to participate in activities of daily living; tachycardia, palpitations with activity; elevated blood pressure with activity; shortness of breath with activity, dyspnea (labored breathing, wheezing); chest discomfort with activity; dizziness; pallor; diaphoresis; light-headedness.
Bleeding, risk (related to altered clotting factors)Cool extremities, delayed capillary refill, decreased distal pulses, altered mental status, hypotension, tachycardia, decreased level of consciousness. Bruises easily, hematemesis, weakness, shortness of breath, bloody or black stools. PT prolonged greater than 13.5 seconds.
Fall, risk (related to impaired mobility, assistive device use, acute or chronic disease process, dizziness, confusion, history of previous falls)Unsteady gait; decreased ability to complete activities of daily living independently, decreased visual acuity, or hearing; fatigue; weakness; difficulty following instructions; improper assistive device use; altered color perception; changed center of gravity; delayed response and reaction times
Fatigue (related to deficient metabolic energy production associated with faulty metabolism and storage of nutrients, decreased nutritional intake, decreased nutrient utilization)Weakness, lethargy, complaints of tiredness, inability to perform activities of daily living, irritability, agitation, falls asleep during normal waking hours, complains of lack of energy
Gas exchange, risk (ineffective—related to blood loss secondary to ineffective clotting factors, increased abdominal girth secondary to liver cirrhosis)Orthopnea, dyspnea, shortness of breath at rest or with activity, pallor, shallow respirations, cyanosis, altered blood gas, increasing abdominal girth
Nutrition (insufficient nutrition related to the inability to ingest or digest food, fatigue, energy loss, no interest in eating, abdominal pain)Decreased serum total protein and albumin, weight loss, deceased dietary intake, weakness, lack of interest in food or eating, pale mucous membranes, mouth sores, fatigue, listlessness, fatty stools, pale mucous membranes, stool clay colored or melena, dark foul smelling urine; decreased muscle tone
Skin, risk (related to elevated serum bilirubin levels and excess bile salt resulting in tissue irritation and histamine release, jaundice associated with liver disease)Reports itchy skin (dermatitis/pruritis), chronic scratching, dry scaly skin, yellow skin and sclera, visible scratch marks with or without scabbing, rash

Before the Study: Planning and Implementation


Teaching the Patient What to Expect

  • Explain that this test can assist in assessing liver function.
  • Explain that a blood sample is needed for the test.

Potential Nursing Actions

  • Measuring and trending abdominal girth can assist in monitoring the progression of ascites with liver disease.

After the Study: Implementation & Evaluation Potential Nursing Actions


Avoiding Complications

  • The patient with cirrhosis should be observed carefully for the development of ascites, in which case fluid and electrolyte balance requires strict attention.

Treatment Considerations

General

  • Monitor and trend AST. Compare with LFTs (ALT, Alb, ALP, TBil, DBil, TP) or other related studies to track the course of disease and response to treatment.
  • Note that PT will be prolonged and INR increased if liver function is significantly damaged.
  • Monitor and trend gamma-glutamyltransperase (GGTP), bilirubin, total protein, iron, electrolytes, folic acid, vitamin K, and thiamine in the presence of hepatitis.

Activity

  • Assess for normal baseline level of activity and nutritional status.
  • Assess cardiopulmonary status prior to activity.
  • Use pulse oximetry to monitor oxygen status with activity.
  • Assess the need for assistive equipment prior to activity (walker, cane, etc.).
  • Consider fall precaution strategies (gait-belt, 1:1 assistance).
  • Monitor sleep pattern to assess level of fatigue.

Bleeding, Risk

  • Take frequent vitals signs to monitor for changes outside of patient’s baseline.
  • Monitor for bleeding symptoms (stools, emesis, bruising).
  • Monitor for shortness of breath; administer oxygen as ordered.
  • Administer ordered blood or blood products per facility protocol.

Fall, Risk

  • Assess fall risk on admission, transfer, post-fall, and change of condition.
  • Follow established organizational fall prevention protocols.
  • Identify previous fall history and frequency.
  • Assess for disease-related symptoms such as orthostatic hypotension or urinary incontinence.
  • Move the patient closer to the nurses station for easier observation.
  • Enlist the support of reliable family members as partners in preventing falls.
  • Move frequently used items close to the bed to decrease desire to get up.
  • Answer call lights timely to decrease risk of getting up.
  • Place the bed in the lowest possible position.
  • Raise side rails judiciously as the situation requires.
  • Encourage the use of well-fitting shoes with nonskid soles.
  • Light the room well to prevent tripping.
  • Review medications to identify any pharmacological contributors to fall risk.
  • Encourage the use of eyeglasses, hearing aids, assistive devices.

Fatigue

  • Obtain a history of normal activity level for baseline comparison.
  • Pace activities to encourage periods of rest, conserving oxygen and decreasing metabolic demands.
  • Planned activities should be spaced away from meal times to prevent exhaustion for affecting nutritional intake.
  • Assess activity tolerance and increase as tolerated.
  • Limit visitors to prevent exhaustion as socialization contributes to fatigue.
  • Teach how to manage energy effectively.
  • Encourage small, frequent meals; keep frequently used items within reach.
  • Administer ordered acid suppression medications, antiemetics, and antidiarrheals.

Gas Exchange, Risk

  • Monitor pulse oximetry, administer oxygen as ordered.
  • Position in high Fowler to maximize lung expansion.
  • Obtain baseline abdominal girth, measure and mark each shift or as needed to monitor growth.
  • Consider use of incentive spirometry.
  • Encourage deep breathing and repositioning.

Nutrition

  • Facilitate management of insufficient nutrition.
  • Facilitate speech therapy consult if impaired swallowing is noted.
  • Record daily weight, calorie count. Consider counseling, dietary consult.
  • Assess current eating patterns and attitudes toward food.
  • Monitor and trend laboratory values associated with nutrition, serum albumin, transferrin, RBC count, WBC count, electrolytes.
  • Facilitate a pleasant eating environment.
  • Consider championship during meals to enhance appetite.
  • Provide culturally appropriate foods from home.
  • Discourage caffeinated or carbonated drinks as they may sate the appetite.
  • Administer ordered nutrition supplements.

Skin, Risk

  • Assess skin general condition noting any scratches, bruises, excoriation, rash.
  • Monitor bilirubin level as a level greater than 3 mg/dL facilitates jaundice and increases itching risk.
  • Discuss ways to protect the skin such as use of tepid water, alkaline soap, and emollient lotions.
  • Suggest keeping short fingernails and the use of mittens to discourage scratching.
  • Discuss how loose-fitting cotton clothing, cool room temperatures, and administration of antihistamines can help decrease itching.
  • Assess for easy bruising.

Nutritional Considerations

  • Increased AST levels may be associated with liver disease.
  • Encourage eating a well-balanced diet that includes foods high in fiber.
  • Dietary recommendations will vary depending on the condition and its severity. For example, recommend a diet of soft foods if esophageal varices develop, fat substitutes for bile duct disease, or limitations on salt intake if ascites develop.
  • Monitor and trend laboratory values that evaluate nutritional status (Alb, TP, K+), and collaborate with HCP on replacement strategies.
  • Administer ordered enteral or parenteral nutrition and evaluate the patient’s response.
  • Correlate laboratory values with IV fluid infusion and collaborate with the HCP and pharmacist to adjust enteral and parenteral nutrition to patient caloric needs.
  • Facilitate adequate pain and nausea control to improve caloric intake.
  • Consider supplementation of diet with vitamins and folic acid.

Clinical Judgement

  • Consider the best common sense approach to implement fall precautions in a culturally sensitive manner that will foster patient and family adoption and adherence, thereby decreasing potential injury.

Followup Evaluation and Desired Outcomes

  • Agrees to cease drinking alcohol if substance use disorder (alcohol) is a causal factor in disease development.
  • Seeks support from family, community, faith-based, or medical professional to assist in remaining free from substance use disorder (alcohol) and maintenance of positive lifestyle changes.
  • Acknowledges the importance of patient and/or family reporting respiratory infection, bleeding, skin breakdown, changes in personality, increasing stupor, or lethargy to the HCP.
  • Seeks psychological counseling to address, fear, anxiety, or depression associated with diagnosis and prognosis.