♦ To detect acute hepatic disease, especially hepatitis and cirrhosis without jaundice, and evaluate its treatment

♦ To distinguish between myocardial and hepatic tissue damage (with aspartate aminotransferase)

♦ To assess the hepatotoxicity of some drugs

8 to 50 units/L (SI, 0.14 to 0.85 µkat/L)

♦ Alanine aminotransferase (ALT) is needed for energy production and is found mainly in the liver, with lesser amounts in the kidneys, heart, and skeletal muscles.

♦ ALT levels may be increased slightly with an acute myocardial infarction. They may be increased slightly to moderately in active cirrhosis and drug-induced or alcoholic hepatitis. And they may be very high in viral hepatitis, severe drug-induced hepatitis, or other hepatic disease with extensive necrosis.

45 to 115 units/ml (SI, 45 to 115 units/L)

♦ Alkaline phosphatase (ALP) is an enzyme that affects bone calcification and lipid and metabolite transport.

♦ An elevated ALP level usually indicates skeletal disease or extrahepatic or intrahepatic biliary obstruction causing cholestasis.

♦ Tell the patient to fast for at least 8 hours before the test.

♦ To diagnose acute pancreatitis

♦ To distinguish between acute pancreatitis and other causes of abdominal pain that warrant immediate surgery

♦ To evaluate possible pancreatic injury caused by abdominal trauma or surgery

26 to 102 units/L (SI, 0.4 to 1.74 µkat/L)

♦ Amylase (AML) helps digest starch and glycogen in the mouth, stomach, and intestine.

♦ Measurement of serum or urinary AML is the most important laboratory test in cases of suspected acute pancreatic disease.

♦ After the onset of acute pancreatitis, AML levels rise within 2 hours, peak within 12 to 48 hours, and return to normal within 3 to 4 days.

♦ Levels may be increased moderately in obstruction of the common bile duct, pancreatic duct, or ampulla of Vater; pancreatic injury from a perforated peptic ulcer; pancreatic cancer; or acute salivary gland disease.

♦ To evaluate the efficiency of pulmonary gas exchange

♦ To assess the integrity of the ventilatory control system

♦ To determine the acid-base level of the blood

♦ To monitor respiratory therapy

PaO₂: > 80 mm Hg (SI, > 10.6 kPa)

PaCO₂: 35 to 45 mm Hg (SI, 4.7 to 5.3 kPa)

pH: 7.35 to 7.45 (SI, 7.35 to 7.45)

O₂ content: 15 to 22 vol % (SI, 0.15 to 0.23 mmol/L)

SaO₂: > 94% (SI, > 0.94)

HCO₃−: 22 to 26 mEq/L (SI, 22 to 26 mmol/L)

♦ Arterial blood gas (ABG) analysis measures the partial pressure of arterial oxygen (PaO₂), partial pressure of arterial carbon dioxide (PaCO₂), pH of an arterial sample, oxygen content (O₂CT), arterial oxygen saturation (SaO₂), and bicarbonate (HCO₃⁻) level.

♦ Blood for ABG analysis may be drawn by percutaneous arterial puncture or through an arterial line.

♦ Low PaO₂, O₂CT, and SaO₂ levels and a high PaCO₂ may result from conditions that impair respiratory function and airway obstruction.

♦ Low readings may result from obstruction of the bronchioles, an abnormal ventilation to perfusion ratio, or alveoli that are damaged or filled with fluid.

♦ Low O₂CT—with normal PaO₂, SaO₂ and, possibly, PaCO₂ values—may result from severe anemia, decreased blood volume, and reduced capacity to carry hemoglobin oxygen.

♦ ABG values also give information about acid-base disorders.

♦ To aid detection and differential diagnosis of acute hepatic disease

♦ To monitor the progress and prognosis of patients with cardiac and hepatic diseases

♦ To aid diagnosis of myocardial infarction (MI) along with creatine kinase and lactate dehydrogenase levels

12 to 31 units/L (SI, 0.14 to 0.78 µkat/L)

♦ Aspartate aminotransferase (AST) is essential to energy production and is found in many cells, mainly in the liver, heart, skeletal muscles, kidneys, pancreas, and red blood cells.

♦ AST is released into serum in proportion to cellular damage. Levels increase early in a disease process, are most increased during the most acute phase, and decrease as the disease resolves.

♦ Moderate to high levels (5 to 10 times normal) may indicate dermatomyositis, Duchenne’s muscular dystrophy, or chronic hepatitis.

♦ High levels (10 to 20 times normal) may indicate severe MI, severe infectious mononucleosis, or alcoholic cirrhosis.

♦ Extreme elevations (more than 20 times normal) may indicate acute viral hepatitis, severe skeletal muscle trauma, extensive surgery, drug-induced hepatic injury, or severe passive liver congestion.

♦ Tell the patient that the test usually involves three venipunctures over 3 days.

♦ To evaluate liver function

♦ To aid in diagnosing jaundice and monitoring its progress

♦ To aid in diagnosing biliary obstruction and hemolytic anemia

♦ To determine whether a neonate needs an exchange transfusion or phototherapy because of dangerously high levels of unconjugated bilirubin

Total: 0.3 to 1 mg/dl (SI, 5 to 17 µmol/L)

Conjugated (direct): <0.5 mg/dl (SI, <6.8 µmol/L)

Unconjugated (indirect): 1.1 mg/dl (SI, 19 µmol/L)

Total: 2 to 12 mg/dl (SI, 34 to 205 µmol/L)

Conjugated (direct): 0 to 0.8 mg/dl (SI, 0 to 136 µmol/L)

Unconjugated (indirect): 0 to 10 mg/dl (SI, 0 to 170 µmol/L)

♦ Bilirubin is the main bile pigment and major product of hemoglobin catabolism.

♦ Unconjugated bilirubin may accumulate in a neonate’s brain, causing irreparable damage.

♦ Increased indirect serum bilirubin levels may indicate hepatic damage, severe hemolytic anemia, and congenital enzyme deficiencies.

♦ Increased direct serum bilirubin levels usually indicate biliary obstruction.

♦ In neonates, increased total bilirubin levels may indicate the need for an exchange transfusion.

♦ Adults should fast for at least 4 hours before the test.

♦ To evaluate kidney function and diagnose renal disease

♦ To aid in assessing hydration

8 to 20 mg/dl (SI, 2.9 to 7.5 mmol/L)

5 to 18 mg/dl (SI, 1.8 to 6.4 mmol/L)

8 to 23 mg/dl (SI, 2.9 to 8.2 mmol/L)

♦ Blood urea nitrogen (BUN), the chief end-product of protein metabolism, is formed in the liver from ammonia and excreted by the kidneys.

♦ BUN level reflects protein intake and renal excretory capacity but is a less reliable indicator of uremia than the serum creatinine level.

♦ BUN levels are increased in renal disease, reduced renal blood flow, urinary tract obstruction, and increased protein catabolism.

♦ BUN levels are decreased with severe hepatic damage, malnutrition, and overhydration.

♦ To evaluate endocrine function, calcium metabolism, and acid-base balance

♦ To guide therapy in patients with renal failure, renal transplant, endocrine disorders, malignancies, cardiac disease, and skeletal disorders

Total calcium: 8.2 to 10.2 mg/dl (SI, 2.05 to 2.6 mmol/L)

Ionized calcium: 4.65 to 5.28 mg/dl (SI, 1.16 to 1.32 mmol/L)

Total calcium: 8.6 to 11.2 mg/dl (SI, 2.2 to 2.7 mmol/L)

Ionized calcium: 4.4 to 5.52 mg/dl (SI, 1.2 to 1.38 mmol/L)

♦ About 1% of the body’s total calcium circulates in the blood; of this, about 50% is bound to plasma proteins and 40% is ionized, or free.

♦ The serum calcium level reflects the total amount of calcium in the blood; the ionized calcium level reflects the fraction of serum calcium in ionized form.

♦ Hypercalcemia may occur with hyperparathyroidism and parathyroid tumors, Paget’s disease of the bone, multiple myeloma, metastatic carcinoma, multiple fractures, prolonged immobilization, inadequate calcium excretion, excessive calcium ingestion, and overuse of antacids.

♦ Hypocalcemia may result from hypoparathyroidism, total parathyroidectomy, malabsorption, Cushing’s syndrome, renal failure, acute pancreatitis, peritonitis, malnutrition with hypoalbuminemia, renal failure, and blood transfusions.

♦ In the patient with hypocalcemia, be alert for circumoral and peripheral numbness and tingling, muscle twitching, Chvostek’s sign (facial muscle spasm), tetany, muscle cramping, Trousseau’s sign (carpopedal spasm), seizures, arrhythmias, laryngeal spasm, decreased cardiac output, prolonged bleeding time, fractures, and prolonged QT interval.

♦ To assess the risk of coronary artery disease (CAD)

♦ To evaluate fat metabolism

♦ To aid diagnosis of nephrotic syndrome, pancreatitis, hepatic disease, hypothyroidism, and hyperthyroidism

♦ To assess the efficacy of lipid-lowering drug therapy

Females: <190 mg/dl (SI, < 4.9 mmol/L)

Males: <205 mg/dl (SI, <5.3 mmol/L)

<170 mg/dl (SI, <4.39 mmol/L)

♦ Total cholesterol test measures the circulating levels of free cholesterol and cholesterol esters.

♦ Instruct the patient not to eat or drink for 12 hours before the test.

♦ Elevated serum cholesterol levels may indicate a risk of CAD as well as incipient hepatitis, lipid disorders, bile duct blockage, nephrotic syndrome, obstructive jaundice, pancreatitis, and hypothyroidism.

♦ Low serum cholesterol levels commonly reflect malnutrition, cellular necrosis of the liver, or hyperthyroidism.

♦ To detect and diagnose acute myocardial infarction (MI) and reinfarction (mainly using the CK-MB isoenzyme)

♦ To evaluate causes of chest pain and monitor the severity of myocardial ischemia after cardiac surgery, cardiac catheterization, and cardioversion (mainly using CK-MB)

♦ To detect early dermatomyositis and musculoskeletal disorders that aren’t neurogenic in origin, such as Duchenne’s muscular dystrophy (mainly using total CK)

Females: 30 to 135 units/L (SI, 0.51 to 2.38 µkat/L)

Males: 55 to 170 units/L (SI, 0.94 to 2.9 µkat/L)

2 to 4 times adult values

CK-MM (CK₃): 90% to 100% (SI, 0.9 to 1.0)

CK-MB (CK₂): <5% (SI, <0.05)

CK-BB (CK₁): 0%

♦ Creatine kinase (CK) reflects normal tissue catabolism; increased serum levels indicate trauma to cells.

♦ Measuring CK isoenzymes localizes the site of tissue destruction: CK-BB is mostly found in brain tissue, CK-MM and CK-MB in skeletal and heart muscle. CK-MB and CK-MM isoenzymes can be assayed to increase the sensitivity of the test.

♦ Tell a patient being evaluated for musculoskeletal disorders to avoid exercising for 24 hours before the test.

♦ Detectable CK-BB isoenzyme may indicate brain tissue injury, widespread malignant tumors, severe shock, or renal failure.

♦ CK-MM values increase after skeletal muscle trauma; with dermatomyositis, muscular dystrophy, and hypothyroidism; and following muscle activity caused by agitation, such as during acute psychosis.

♦ CK-MB levels >5% of the total CK level indicate MI, especially if the lactate dehydrogenase isoenzyme ratio is >1. In acute MI, CK-MB increases in 2 to 4 hours, peaks in 12 to 24 hours, and returns to normal in 24 to 48
hours; total CK level follows a similar pattern but increases slightly later.

♦ Total CK levels may increase in severe hypokalemia, carbon monoxide poisoning, malignant hyperthermia, and alcoholic cardiomyopathy; after a seizure; and, occasionally, with pulmonary or cerebral infarction.

♦ To assess renal function (mainly glomerular filtration)

♦ To monitor the progression of renal insufficiency

Females: 72 to 110 ml/minute/1.73 m² (SI, 0.69 to 1.06 ml/s/m²)

Males: 94 to 140 ml/minute/1.73 m² (SI, 0.91 to 1.35 ml/s/m²)

♦ Creatinine is the main end-product of creatine, and its production is proportional to total muscle mass.

♦ Creatinine clearance is an excellent diagnostic indicator of renal function and becomes abnormal when more than 50% of the nephrons have been damaged.

♦ Low creatinine clearance may result from reduced renal blood flow, acute tubular necrosis, acute or chronic glomerulonephritis, advanced bilateral chronic pyelonephritis, advanced bilateral renal lesions, nephrosclerosis, heart failure, or severe dehydration.

♦ Before the test, tell the patient to avoid meat, poultry, fish, tea, and coffee for 6 hours; to avoid strenuous physical exercise during the test; and to expect a timed urine specimen and at least one blood sample.

♦ To assess glomerular filtration

♦ To screen for renal damage

Females: 0.6 to 0.9 mg/dl (SI, 53 to 97 µmol/L)

Males: 0.9 to 1.3 mg/dl (SI, 62 to 115 µmol/L)

0.5 to 1 mg/dl (SI, 44 to 88 µmol/L)

♦ Creatinine is an end-product of creatine metabolism that appears in serum in amounts proportional to muscle mass and provides a more sensitive measure of renal damage than BUN levels.

♦ Elevated serum creatinine levels usually indicate renal disease that has seriously damaged 50% or more of nephrons.

♦ To monitor inflammatory or malignant disease

♦ To aid in detecting and diagnosing such diseases as tuberculosis, tissue necrosis, and connective tissue disease

Females: 0 to 20 mm/hour (> age 50: 0 to 30 mm/hour)

Males: 0 to 10 mm/hour (> age 50: 0 to 20 mm/hour)

0 to 10 mm/hour

♦ Erythrocyte sedimentation rate (ESR) measures the degree of erythrocyte settling that occurs in a blood sample during a specified amount of time and is a sensitive but nonspecific early indicator of disease.

♦ ESR usually increases significantly in widespread inflammatory disorders.

♦ It also increases in pregnancy, anemia, acute or chronic inflammation, tuberculosis, paraproteinemias, rheumatic fever, rheumatoid arthritis, and some cancers.

♦ ESR may be depressed in polycythemia, sickle cell anemia, hyperviscosity, and low plasma fibrinogen or globulin levels.

♦ To screen for diabetes mellitus

♦ To monitor drug or diet therapy in patients with diabetes mellitus

≤100 mg/dl (SI, ≤5.6 mmol/L)

60 to 100 mg/dl (SI, 3.3 to 5.6 mmol/L)

♦ Fasting plasma glucose test measures plasma glucose levels after a 12- to 14-hour fast.

♦ Fasting plasma glucose levels of 126 mg/dl (SI, 7 mmol/L) or more obtained on two or more occasions confirms diabetes mellitus.

♦ A 2-hour postprandial plasma glucose test or an oral glucose tolerance test may be performed to confirm the diagnosis in a patient with borderline or transiently elevated levels.

♦ To aid in diagnosing diabetes mellitus

♦ To monitor drug or diet therapy in patients with diabetes mellitus

<145 mg/dl (SI, <8 mmol/L)

Levels slightly elevated

♦ The 2-hour postprandial blood glucose test is performed when the patient shows symptoms of diabetes (polydipsia and polyuria) or when the results of the fasting plasma glucose test suggest diabetes.

♦ Two 2-hour postprandial blood glucose values of 200 mg/dl (SI, 11.1 mmol/L) or above indicate diabetes mellitus.

♦ Tell the patient to eat a balanced meal or one containing 100 g of
carbohydrates before the test and then to fast for 2 hours. Instruct him to avoid smoking and strenuous exercise after the meal.

♦ To confirm the diagnosis of diabetes mellitus in selected patients

♦ To aid in diagnosing hypoglycemia and malabsorption syndrome

30-minute to 1-hour plasma glucose level: 160 to 180 mg/dl (SI, 8.8 to 9.9 mmol/L)

2-hour plasma glucose level after glucose load: <138 mg/dl (SI, <7.7 mmol/L)

3-hour plasma glucose level after glucose load: 70 to 120 mg/dl (SI, 3.9 to 6.7 mmol/L)

2-hour plasma glucose level after glucose load: <140 mg/dl (SI, <7.8 mmol/L)

♦ The oral glucose tolerance test is the most sensitive method of evaluating borderline cases of diabetes mellitus.

♦ Plasma and urine glucose levels are monitored for 3 hours after the patient ingests a challenge dose of glucose.

♦ Decreased glucose tolerance, in which glucose levels peak sharply before falling slowly to fasting levels, may confirm diabetes mellitus or result from Cushing’s disease, hemochromatosis, pheochromocytoma, or central nervous system lesions.

♦ Increased glucose tolerance, in which levels may peak at less than normal, may indicate insulinoma, malabsorption syndrome, adrenocortical insufficiency, hypothyroidism, or hypopituitarism

♦ Instruct the patient to maintain a high-carbohydrate diet for 3 days and then fast for 10 to 16 hours before the test.

♦ Tell the patient not to smoke, drink coffee or alcohol, or exercise strenuously for 8 hours before or during the test.

♦ To aid in diagnosing polycythemia, anemia, or abnormal states of hydration

♦ To aid in calculating red blood cell (RBC) indices

Females: 36% to 48% (SI, 0.36 to 0.48)

Males: 42% to 52% (SI, 0.42 to 0.52)