Blood Chemistry Testing

Blood chemistry testing is defined simply as identifying the numerous chemical substances found in the blood. The analysis of these substances will provide clues to the functioning of the major body systems. Most nurses are concerned with the fact that many blood chemistry tests are performed on the serum derived from whole blood. Serum, of course, is the liquid remaining after whole blood has clotted in the sample tube. Some blood chemistry tests are performed on other parts of blood as well.

Many laboratories now use automated electronic systems, such as the Sequential Multiple Analyzer (SMA) 12/60 and the Sequential Multiple Analyzer with Computer (SMAC). These machines are used for blood chemistry procedures, blood banking, serological procedures, and bacteriologic procedures. These systems perform blood studies rapidly, economically, and comprehensively. They can detect unsuspected abnormalities and indicate the need for additional tests.

The SMA 12/60 can make 12 determinations on 60 serum specimens in one hour. The SMAC can perform 20 to 40 biochemical determinations on 120 serum specimens in one hour. The SMAC can perform complete blood chemistry profiles in a short time and on very little blood.

Prior to taking the blood sample, the nurse should inform the patient about the test(s) to be performed and the preparation for the test. You should:

1. define and explain the test
2. state the specific purpose of the test
3. explain the procedure
4. discuss test preparation, procedure, and posttest care

Some of the more common tests require no special preparation. However, some blood chemistry tests will have specific requirements such as dietary restrictions or medication restrictions. For some tests, such as hormones, stress should be avoided prior to the test. Be sure to inform the patient of any special preparation prior to the venipuncture and any posttest care needed.

Cardiac Enzymes and Proteins

Introduction:

Enzymes are proteins in the body and they act as catalysts. Catalysts are substances which change chemical reactions and rates of these reactions in the body. With their presence, reactions are either slowed or speeded.

Enzymes are found in all body cells and in other places in the body. When limiting our discussion to the cardiac enzymes, we are referring to the enzymes released into the bloodstream during myocardial damage. These enzymes can be used in the diagnosis of an MI. These blood tests are considered blood chemistry tests. However, we include them here as a separate chapter because they are so unique.

The term isoenzyme will also be used in this section. An isoenzyme (also known as Isozyme) is an enzyme that may appear in multiple forms, with slightly different chemical or other characteristics, and be produced in different organs, although each enzyme performs essentially the same function. The various forms are distinguishable in analysis of blood samples, which aids in the diagnosis of disease. Isoenzymes that catalyze the same physiologic reaction may also appear in different forms in different animal species.

To summarize, a protein enzyme is composed of (one or more) "isoenzyme." These isoenzymes are very similar to each other in chemical composition, but have diferences that can be measured by certain lab tests. For example, the CPK enzyme has three distinct isoenzymes. These isoenzymes are:

1. CK-BB (CK1) Isoenzyme #1
2. CK-MB (CK2) Isoenzyme #2
3. CK-MM (CK3) Isoenzyme #3

All three of these isoenzymes make up the main enzyme CPK (creatine phosphokinase) (also called CK--creatine kinase). However, as we will discuss later in this section, each isoenzyme can be isolated to different organs in the body and can help in diagnosing certain disorders.

Following are the main cardiac enzymes:

1. SGOT
2. LDH (also called LD)
3. CPK (also called CK)

Test: SGOT

Serum Glutamic Oxaloacetic Transaminase, called: AST, (Aspartate Aminotransferase) A blood chemistry test for the level of SGOT in blood (is released with tissue necrosis).

Normal Values: 5-40 U/ml (Frankel) 4-36 IU/L; or 16-60 (Karmen) U/ml U/L at 30 degrees C; or 8-33 (SI units) at 37 degrees C.

Clinical Implications:

This enzyme shows an elevation 8-12 hours after infarction. Peak levels are reached 24-48 hours after the MI. This enzyme is not particularly indicative of an MI. Other conditions can also cause a rise in the levels. High levels of SGOT may be obtained with trauma to the skeletal muscles, in liver disease, pancreatitis and others. SGOT is found in: heart muscle, liver, some also in skeletal muscle, kidneys and the pancreas. Demerol and morphine may elevate the levels temporarily. This enzyme then, is used with other enzyme results to more definitely diagnose the MI. AST levels elevate in 6-10 hours following acute MI. They peak in 24 to 48 hours.

*Please note that decreased levels of enzyme are found in pregnancy, diabetic ketoacidosis, beriberi. Elevations can be caused by hepatitis, trauma, musculoskeletal disease, IM injection, pancreatitis, liver cancer, and strenuous exercise.
*Explain purpose of test to patient
*do not give IM injections before the blood tests; and if serial specimens are taken, still give no IM injections, remember that very few meds can be given that do not affect the AST levels.

Test: LDH, Lactic Dehydrogenase ( also called LD)

An intracellular enzyme present in nearly all metabolizing cells in the body. The highest concentration of enzyme is located in the heart, skeletal muscle, liver, kidney, brain, and erythrocytes. There are 5 isoenzymes of LDH. This is a blood chemistry test to measure the amount of enzyme in the blood.

LDH catalyzes the reversible conversion of muscle lactic acid into pyruvic acid, an essential step in the metabolic process that ultimately produce cellular energy. Because LDH is present in almost all body tissues, cellular damage increases total serum LDH, limiting the diagnostic usefulness of this test.

Isoenzymes LD1 and LD2 appear primarily in the heart, red blood cells and kidneys. LD3 is primarily in the lungs. LD4 and LD5 are located in the liver, skin, and the skeletal muscles.

Normal Values:
Total LDH: 150-450 U/ml (Wroblewski-LaDue method), 60-120 U/ml (Wacker method) 70-200 IU/L--results are different according to method used. Always check your own hospital for results used. These values have a wide range of normal and abnormal results.

Newborn: 300-1500IU/L Child: 50-150 IU/L

• LD1---17.5% to 28.3% of total
• LD2---30.4% to 36.4% of total
• LD3---19.2% to 24.8% of total
• LD4----9.6% to 15.6% of total
• LD5----5.5% to 12.7% of total

Because many common diseases increase total LDH (LD) levels, isoenzyme electrophoresis is usually necessary for diagnosis. In some disorders, total LDH may be within normal limits, but abnormal proportions of each enzyme indicate specific organ tissue damage. For example, in acute MI, the LD1 and LD2 isoenzyme ratio is typically greater than 1 within 12 to 48 hours after onset of symptoms (known as flipped LD). Midzone fractions (LD2, LD3, LD4) can be increased in granulocytic leukemia, lymphomas, and platelet disorders.

Clinical Implications:

The total LDH may be influenced by other body tissues, other than the heart. Therefore, the LDH is split into its fractions, isoenzymes, in order to isolate the particular one which is located almost solely in the myocardium. This isoenzyme is the number 1 isoenzyme. Although not foolproof, if this isoenzyme is elevated, it is strongly indicative of an MI. LDH elevates in 24-48 hours and peaks in 48-72 hours after the episode.

Narcotic drugs and IM injections can elevate serum LDH levels. Hemolysis of the blood can cause an elevated LDH because LDH is plentiful in the erythrocytes.

Again, with this enzyme, it is important to gather a detailed patient history. Find out if there has been injury to any systems which might elevate the LDH levels. These include: trauma, cancers, leukemia, hepatitis, shock, heat stroke, sickle cell disease.

Test: CPK, Creatine Phosphokinase (CK) Creatine Kinase

This is a blood chemistry test to measure the amount of enzyme in the blood. The CPK enzyme is found in high concentration in heart and skeletal muscle; low concentration is brain tissue. CPK is an enzyme that catalyzes the creatine-creatinine metabolic pathway in muscle cells and brain tissue. Because of its intimate role in energy production, CPK reflects normal tissue catabolism; increased serum levels indicate trauma to cells.

Normal Values:
male: 5-35 ug/ml (mcg/ml);
female: 5-25 ug/ml
newborn: 10-300 IU/L

Clinical Implications:

Serum CPK/CK will be elevated in skeletal muscle disease, in acute MI, in cerebral vascular disease, vigorous exercise, IM injections, electrolyte imbalance, and hypokalemia. CPK has three isoenzymes as presented earlier. Fractionation and measurement of these three distinct CPK isoenzymes have replaced the use of total CK (or CPK) levels to accurately localize the site of increased tissue destruction. CK-BB is most often found in brain tissue. CK-MM and CK-MB are found primarily in skeletal and heart muscle. In addition, subunits of CK-MB and CK-MM, called isoforms or isoenzymes, can be assayed to increase the test's sensitivity.

These isoenzymes are:

1. CK-BB (CK1) Isoenzyme #1
2. CK-MB (CK2) Isoenzyme #2
3. CK-MM (CK3) Isoenzyme #3

When the isoenzyme CPK-MB is elevated, greater than 5%, it could strongly indicate damage to the myocardial cells. The CPK-MB elevates within 4-6 hours after an acute MI; peaks in 18-24 hours; it then returns to normal within 3-4 days. It is best to avoid IM injections, even though the injections will usually not cause elevation of the CPK-MB. This is because other enzymes can be affected by the injections, and other enzyme studies are performed in conjunction with the CPK studies. Trauma and surgery will elevate the CPK levels.

Precautions:

• Draw the sample before giving or one hour after giving I.M. injections. I.M. injections will increase the total CK level. However, in most clinical situations today, this is not a problem. Most persons admitted with a possible MI will almost always have an intravenous line started and all medications will be given intravenously, not I.M.
• Be sure to obtain the blood samples on schedule. Always note on the laboratory slip, the time the sample was drawn and the hours elapsed since onset of chest pain. Be sure to draw blood samples in a 7-ml red top tube.
• Be sure to handle the sample gently to prevent hemolysis. Always have the sample transported to the lab promptly because CK activity diminishes significantly after 2 hours at room temperature.

Discussion of Cardiac Enzymes

The diagnosis of MI is the main reason for the study of these enzymes. However, from the discussion of each enzyme, you can see that the diagnosis cannot be made quickly. The fact that the enzymes are not exclusively in the cardiac muscle, make the diagnosis very unsure. In the clinical setting, one of the most common reasons for enzyme elevation, is the IM injection. The injection will injure the muscle. The ingestion of alcohol, and trauma could also cause elevations which could cloud the diagnosis.

Isoenzyme assay techniques have become very refined in the recent years. The new techniques of measurement and reporting of the results have made the physician more sure about the diagnosis. The MD must also rely on other data in making the diagnosis. Within 12-24 hours of acute MI episode, a polymorphonuclear leukocytosis develops. Also seen in these cases, is a slight increase in body temperature and a slight increase in the sed rate of the blood. When all of the above data are compiled, an MI may be suspected.

The observant nurse can make very important discoveries about the patient. Be familiar with the test method(s) used at your facility to measure enzymes and isoenzymes. Some labs now report the results on a very sophisticated lab sheet on a graph which will graphically depict normal and abnormal results and will practically diagnose the condition for you.

Test: Myoglobin

This is a blood chemistry test used to measure the amount of this enzyme in the blood. This enzyme is not considered one of the cardiac enzymes. However, myoglobin is often used to help confirm the results of the cardiac enzymes and to help confirm damage to the myocardium.

Normal Values: 30 to 90 NG/ml

Clinical Implications:

This test measures serum levels of myoglobin, an oxygen-binding muscle protein, similar to hemoglobin. Myoglobin is normally found in skeletal muscle and cardiac muscle, and is released into the bloodstream after muscle injury. Thus, serum myoglobin levels help to estimate the amount of muscle damage. However, because myoglobin does not indicate the site of the damage, this test is used only to CONFIRM other tests such as CPK, CPK-MB, and others. Test results must also be correlated with the patient's signs and symptoms.

Do not collect the blood specimen from a patient who recently had an angina attack or undergone cardioversion. Cardioversion or angina attacks may increase myoglobin levels. Performing this test immediately after an MI produces misleading results, since myoglobin levels do not peak for 4 to 8 hours. A radioactive scan performed within one week before the test may affect the results. Myoglobin levels are also increased with skeletal muscle injury, polymyositis, dermatomyositis, systemic lupus erythematosis, shock, and in severe renal failure.

Serum Electrolytes

Introduction:

Serum electrolytes are mineral salts dissolved in water (the blood). The electrolytes are found throughout the entire body. These salt solutions have special properties in our bodies. They play an important part in the maintenance of all body functions. From a nursing point of view, it is imperative that we know the impact of these electrolytes on the human body.

Electrolyte determination can be a very important part of the management of the patient with dehydration and many other related disorders. To review the nursing responsibilities: (1) be sure the blood specimen is not drawn from an arm which has an IV running, (2) note if the patient has had a large meal high in sodium, (3) note if they are on a special diet restricting sodium or other nutrients, (4) any other condition such as diabetes which might influence the test results, (5) watch carefully for signs of fluid or electrolyte imbalance. Be sure to perform a complete head-to-toe assessment paying particular attention to cardiac assessment and vital signs.

Test: Sodium, (Na Serum)

This is a lab test which measures the level of serum sodium. Sodium is the major cation in the extracellular fluid; and it is noted for its water-retaining property.

Normal Values:
adult: 135-145 mEq/L (same for child)
infants: 134-150 mEq/L

Clinical Implications:

There is no special patient preparation. However, if the patient has eaten a meal with a very high sodium content in the past 24 hours, this should be noted because it may affect the test. A serum sodium test is rarely ordered alone. This test is usually a part of a panel of electrolyte tests ordered at the same time. The same is true for the other electrolytes mentioned in this section.

This electrolyte has many functions in the body, including: conduction of neuromuscular impulses via sodium pump, (sodium shifts into cells as the potassium shifts out for cellular activity); enzyme activity, osmolality of intravascular fluid; the regulation of acid-base balance, and others.

Decreased levels (hyponatremia) may be caused by: vomiting, diarrhea, gastric suction, excessive perspiration, continuous IV 5% Dextrose/water; low-sodium diet, burns, inflammatory reactions, tissue injury, others.

Increased sodium can mean: dehydration, severe vomiting & diarrhea, CHF, Cushing's disease, hepatic failure, high-sodium diet, and others.

Test: Potassium, (K+)

Definition: Serum electrolyte

Normal Values: 3.5-5.0 mEq/L

Clinical Implications:

Potassium is another of the important electrolytes in the body. Our body is quite sensitive to abnormal levels of potassium. Cardiac arrhythmias and neurological disturbances are seen with high or low levels of this electrolyte. Hypokalemia can be caused by decreased intake, protracted vomiting, renal loss, cirrhosis and others. Hyperkalemia can be caused by renal failure and other causes. The nurse must carefully check vital signs of any patients in the above risk groups, especially the cardiac status and mental status.

Test: Chloride, (Cl)

Definition: Serum electrolyte

Normal Values: 95-105 mEq/L

Clinical Implications:

Chloride anion is found mainly in our extracellular fluid. Chloride plays an important role in fluid balance just as sodium does. Chloride also plays an important role in acid-base balance as well. However, many times the chloride test is ignored; in most cases when the sodium value is normal the chloride value will be normal. So in some hospitals, testing for chloride is not performed very often. Most of the chloride ingested is combined with sodium (sodium chloride-table salt). The normal daily intake of chloride is about 2 g.

Test: Serum Osmolality,

Total amount of active electrolyte particles in solution in the blood.

Normal Values: Adult: 280-300 Osm/kg/H2O.

Clinical Implications:

Serum osmolality measures the number of all dissolved particles in the serum (electrolytes, urea, sugar). It can be helpful in diagnosing fluid and electrolyte imbalances. Sodium will contribute about 90% of the serum osmolality due to its abundance in the body.

There are usually no restrictions for collecting the blood. A random sample is taken for testing. Hyperglycemia will increase the serum osmolality. Decreased osmolality is associated with serum dilution due to overhydration and excessive fluid intake. Increased osmolality is associated with a fluid volume deficit, hypovolemia, dehydration, sodium overload, or hyperglycemia. With increased osmolality, there is thirst, dry mucous membrane, poor skin turgor, and shock-like symptoms.

Test: Acid Phosphatase

Test used to detect prostatic cancer and to monitor response to therapy for prostatic cancer.

Normal Value:
0 to 1.1 Bodanzky units/ml;
1 to 4 King-Armstrong units/ml;
0.13 to 0.63 BLB units/ml.

Clinical Implications:

Acid phosphatase, a group of phosphatase enzymes, appears primarily in the prostate gland and semen. It is also found in other organs, but in very small amounts. Prostatic and erythrocytic enzymes are the two major isoenzymes. They can be separated in the lab. The prostatic isoenzyme is more specific for prostatic cancer. The more widespread the tumor, the more likely it is to produce high serum acid phosphatase levels.

• Marked increased acid phosphatase levels: A tumor that has spread beyond the prostatic capsule
• Moderately increased acid phosphatase levels: Prostatic infarction, Paget's disease, Gaucher's disease, multiple myeloma
• Declining high acid phosphatase levels: Successful treatment of prostatic cancer

Fluorides and phosphates can cause false-negative results. Clofibrate can cause false-positive results. Prostate massage, catheterization, or rectal examination within 48 hours of the test, may interfere with results. Hemolysis due to rough handling of sample or improper storage may interfere with test results. Acid phosphatase levels drop by 50% within one hour if the sample stays at room temperature without the addition of a preservative or if it is not packed in ice.

Test: Ammonia Measures plasma levels of ammonia

Normal value: is less than 50 mcg/dl

Clinical Implications:

This test measures plasma levels of ammonia, a nonprotein nitrogen compound that helps maintain acid-base balance. Most ammonia is absorbed from the GI tract, where it is produced by bacterial action on protein. A smaller amount of ammonia is produced in the kidneys. Normally, the body uses the nitrogen fraction of ammonia to rebuild amino acids. The liver then converts ammonia to urea, for excretion by the kidneys.

In diseases such as cirrhosis of the liver, however, the ammonia can bypass the liver and accumulates in the blood. Therefore, plasma ammonia levels may help indicate the severity of hepatocellular damage.

Precautions:

1. These may cause increased levels of ammonia: acetazolamide, thiazides, ammonium salts, furosemide, hyperalimentation, portacaval shunt
2. These may depress levels of ammonia: lactulose, neomycin, kanamycin
3. Hemolysis of blood sample caused by rough handling may alter the ammonia test results.
4. Before removing pressure from the venipuncture site, make certain bleeding has stopped. Hepatic disease may prolong bleeding time.
5. Fasting specimen is usually required for this test; random samples may also be used (indicate if fasting or random)

Increased plasma ammonia levels:

Seen in hepatic coma, Reye's syndrome, severe congestive heart failure, gastrointestinal hemorrhage, erythroblastosis fetalis

Test: Creatinine

A test for creatinine levels in blood. Creatinine is a nonprotein end product of creatine metabolism. Creatine is an end product of protein metabolism, formed in the liver, kidneys, intestine, pancreas. Test used to assess renal glomerular filtration and screen for renal damage.

Normal Value:
males: 0.8 - 1.2 mg/dl
females: 0.6 - 0.9 mg/dl

Clinical Implications:

This test provides a sensitive measure of renal damage, because renal impairment is virtually the only cause of creatinine elevation. Creatinine is similar to creatine which appears in serum amounts proportional to the body's muscle mass. Unlike creatine, creatinine is easily excreted by the kidneys, with minimal or no absorption by the tubules. Creatinine levels, therefore, are directly related to the glomerular filtration rate. Since creatinine levels normally remain constant, elevated levels usually indicate diminished renal function. Elevated serum creatinine levels are most often seen in patients with renal disease that has seriously damaged 50% or more of the nephrons of the kidneys.

The sample is collected in a standard 10 ml or 15 ml red-top tube. It is ideal to restrict foods and fluids for 8 hours prior to the venipuncture to collect the specimen. Ascorbic acid, barbiturates, and diuretics may raise serum creatinine levels. Patients with exceptionally large muscle masses, such as athletes, may have above-average creatinine levels, even in the presence of normal renal function. Elevated creatinine levels are also seen in persons with Gigantism and Acromegaly.

*Sulfobromophthalein or phenolsulfonphthalein given within the previous 24 hours can elevate serum creatinine levels if the test is based upon the Jaffe reaction.

Blood Groups and Transfusions

All nurses are certainly aware of the ABO blood grouping system. The ABO system is used clinically to type blood for transfusion, in order to assure compatibility. This following section, will deal with the nursing considerations associated with typing of blood and blood products, and the step-by-step process of preparing blood for use by the patient.

Test: Blood Typing

Determination of major blood group a person belongs to. (ABO system)

This test is rapid and simple. It determines the "main" blood type of the person to be transfused. Of course a transfusion is not the only reason a person may be typed. Major blood types are: A, B, AB, and O.

Blood typing in the ABO system, and others, involves the identification of specific proteins that are contained in the blood. Red Blood Cells have either antigen (protein) A, B, or AB or none, on the surface of the cells. These antigens, (proteins) make the blood of each person unique and separate from one another. Blood typing then, categorizes blood in individuals according to these proteins (ABO).

Test: Rh Determination

Definition: test for the Rh factor protein on the RBC, Red Blood Cell.

Normal Values: Most adults (85%) have the Rh factor in their blood, (Rh positive). Only a very small number of persons (15%) do not have the Rh factor (called: Rh negative)

The Rh factor (Rh antigen) was discovered in 1941 by Landsteiner and Weiner using Rhesus monkeys in their research. Since most persons carry the antigen, there are rarely any problems with compatibility of blood. However, most nurses are very aware of the problem seen in the case of erythroblastosis fetalis. In this disorder of the second newborn, the Rh negative mother becomes sensitized to the Rh antigen. If the conditions are right, the infant can be in great trouble.

Test: Crossmatch

Comparison test performed on whole blood in order to ensure compatibility of transfused blood.

Clinical Implications:

Since there are many known and unknown antibodies in our blood, crossmatching is done as a final step before transfusing blood. Simply stated, a crossmatch involves the actual mixing of a sample of the donor's blood with that of the recipient's blood. The mixed samples of blood are then observed for any agglutination which might occur. The process takes 45 minutes to one hour to watch for a reaction.

Some of the above unknown antibodies may cause a reaction in the patient even though the blood has been shown to be compatible in the ABO and Rh systems. Therefore, the two blood specimens are mixed (crossmatched), and if a reaction occurs, there must be some other antigen on the RBC's which is incompatible.