Collection of A Blood Chemistry Specimen

Most blood chemistry tests performed at an outside laboratory require a serum specimen for analysis (Figure 33-1). If the specimen is collected at the medical office, the medical assistant will need to perform a venipuncture using a serum separator tube (SST) or a red-stoppered tube. An example of a blood chemistry profile frequently ordered on patients in the medical office is a comprehensive metabolic profile (CMP). A CMP contains numerous blood chemistry tests and is used primarily in routine health screening of a patient. It is frequently used to detect any changes in the body’s biologic processes that may be present, although the patient may not have had any symptoms to indicate that these changes have occurred. A comprehensive metabolic profile is also used when the patient’s symptoms are so vague that the physician does not have enough concrete evidence to support a clinical diagnosis of a specific organ or disease state. Specimen collection and handling requirements for a comprehensive metabolic profile as presented in a laboratory directory are outlined in Figure 33-2.

Automated Blood Chemistry Analyzers

Automated blood chemistry analyzers are used to perform blood chemistry testing. A blood chemistry analyzer consists of a reflectance photometer that quantitatively measures the amount of chemical substances, or analytes, in the blood. An analyte is defined as a substance that is being identified or measured in a laboratory test. Specifically, a reflectance photometer measures light intensity to determine the exact amount of an analyte in a specimen.

Most physicians consider it too expensive in terms of equipment, supplies, and medical laboratory personnel to perform blood chemistry tests that are any more complex than waived tests in the medical office. These tests are usually performed at an outside laboratory. However, if moderately complex blood chemistry tests are performed in the medical office, a “benchtop” blood chemistry analyzer is typically used to run them; examples of these nonwaived “benchtop” analyzers include the ATAC lab system (Clinical Data, Inc., Newton, Mass) (Figure 33-3) and the Reflotron Chemistry Analyzer (Roche Diagnostics, Branchburg, NJ). Examples of CLIA-waived blood chemistry analyzers that are more commonly used to run blood chemistry tests in the medical office include the Accu-Check Advantage blood glucose meter (Roche Diagnostics), A_1c Now (Bayer Corporation, Morrisville, NJ), and the Cholestech LDX cholesterol system (Cholestech Corporation, Hayward, Calif).

The manufacturer of each blood chemistry analyzer provides an operating manual (and sometimes an instructional video) with the instrument that includes information needed to collect and handle the specimen, perform quality control procedures, and test the specimen. The manufacturer also has personnel available for on-site training and service. Because most medical offices use CLIA-waived blood chemistry analyzers (rather than nonwaived analyzers), the remainder of this chapter focuses on CLIA-waived blood chemistry analyzers used in the medical office.

It is important that the medical assistant become completely familiar with all aspects of the CLIA-waived analyzer used to perform blood chemistry testing in his or her medical office. Medical offices running CLIA-waived tests are required to follow the manufacturer’s instructions exactly for each testing procedure. Instructions include information on the quality control procedures that must be performed when running the test. Quality control procedures are of particular importance to ensure that the analyzer is functioning properly, and that the test results are reliable and accurate. Additional information on quality control procedures is presented below (also refer to the quality control section in Chapter 29).

Quality Control

The ultimate goal when performing blood chemistry testing is to ensure that the test accurately measures what it is supposed to measure; this involves practicing and maintaining a quality control program. Quality control consists of methods and means to ensure that test results are reliable and valid. Two important quality control measures must be performed routinely when a blood chemistry analyzer is used: calibration of the instrument and running controls.

Calibration

Calibration is a mechanism used to check the precision and accuracy of a blood chemistry analyzer, to determine if the system is providing accurate results. A calibration check detects errors caused by laboratory equipment that is not working properly. Calibration is typically performed using a calibration device, often called a standard. The calibration device may come in the form of a calibration strip or cassette. The device is inserted into the analyzer (Figure 33-4, A) and the calibration results are displayed on the LCD screen of the analyzer. The calibration results are then compared with the expected results provided in the product insert or on the calibration device (Figure 33-4, B). If the calibration procedure does not perform as expected, patient testing should not be conducted until the problem has been identified and resolved. The frequency of performing a calibration check is indicated in the manufacturer’s instructions. At a minimum, a calibration check should be performed when a new lot number of testing reagents is put into use.

Controls

A blood chemistry control consists of a solution that is used to monitor a blood chemistry analyzer to ensure the reliability and accuracy of the test results. Controls consist of commercially available solutions with known values. Controls usually come with a product insert, which lists the expected ranges for control results (Figure 33-5); however, expected ranges may sometimes be printed on the containers of the testing reagents. Controls are used to determine if the testing reagents are performing properly and to detect any errors in technique by the individual performing the test.

Generally, two levels of controls must be performed on a blood chemistry analyzer. A low-level control (also known as a Level 1 control) produces results that fall below the reference range for the test; a high-level control (also known as a Level 2 control) produces results that fall above the reference range for the test. The control procedure is performed in a similar manner to the procedure for performing the test on a specimen collected from a patient. Instead of the patient specimen being added to the testing device, however, the control is added to it (Figure 33-6). The control results are compared with expected results provided in the product insert (see Figure 33-5) or on the container of the testing reagents (Figure 33-7).

Failure of a control to produce expected results may be due to the following: deterioration of testing components due to expired testing components or improper storage, improper environmental testing conditions, or errors in the technique used to perform the procedure. If the controls do not perform as expected, patient testing should not be conducted until the problem has been identified and resolved. The frequency of performing controls is indicated in the manufacturer’s instructions. At a minimum, they should be performed on each new lot number of testing reagents, and thereafter on a regular basis, such as monthly.

Blood Glucose

Glucose is the end product of carbohydrate metabolism; it is the chief source of energy for the body. Energy is needed to perform normal functions and to maintain body temperature. The body maintains a constant blood glucose level to ensure a continuous source of energy for the body. Ingested glucose that is not needed for energy can be stored for later use in the form of glycogen in muscle and liver tissue. When no more tissue storage is possible, excess glycogen is converted to triglycerides (a form of fat) and is stored as adipose tissue.

Insulin is a hormone secreted by the beta cells of the pancreas that is required for normal use of glucose in the body. Insulin enables glucose to enter the body’s cells and be converted to energy. Insulin also is needed for the proper storage of glycogen in liver and muscle cells.

Blood Glucose Testing

Measuring the amount of glucose in a blood specimen is one of the most commonly performed blood chemistry tests. It is used to detect abnormalities in carbohydrate metabolism such as those that occur in prediabetes, diabetes, gestational diabetes, hypoglycemia, and liver and adrenocortical dysfunction. Blood glucose is measured by several different testing methods, which include the fasting blood glucose, the 2-hour postprandial blood sugar test, and the oral glucose tolerance test. Each of these methods serves a specific role in diagnosing and evaluating abnormalities in carbohydrate metabolism, and each is described in greater detail here.

Fasting Blood Glucose Test

Blood glucose is usually measured when the patient is in a fasting state. This type of test, termed a fasting blood glucose (FBG), involves collecting a fasting blood sample and measuring the amount of glucose in it. The patient should not have anything to eat or drink except water for 12 hours preceding the test. Certain medications, such as oral contraceptives, salicylates, diuretics, and steroids, may affect the test results; the physician may place the patient on medication restrictions for a specific period before the test—usually 3 days. The patient should be scheduled for the test in the morning to minimize the inconvenience of abstaining from food and fluid.

An FBG is often performed on patients diagnosed with diabetes to evaluate their progress and regulate treatment, and on other patients as a routine screening test to detect prediabetes and diabetes. Prediabetes is the term used to describe the condition in which glucose levels are higher than normal, but not high enough to be classified as diabetes. An individual with prediabetes has an increased risk of developing type 2 diabetes. The American Diabetes Association (ADA) recommends the following guidelines for interpretation of FBG test results:

70-99 mg/dL	Normal
100-125 mg/dL	Prediabetes (also termed impaired fasting glucose)
126 mg/dL or above	Diabetes (confirm by repeating the FBG test on another day)

Two-Hour Postprandial Blood Glucose Test

The 2-hour postprandial blood glucose (2-hour PPBG) test is used to screen for diabetes and to monitor the effects of insulin dosage in patients with diabetes. The patient is required to fast, beginning at midnight preceding the test and continuing until breakfast. For breakfast, the patient must consume a prescribed meal that contains 100 g of carbohydrate, which consists of orange juice, cereal with sugar, toast, and milk. An alternative to this is the consumption of a 100-g test-load glucose solution. A blood specimen is collected from the patient exactly 2 hours after consumption of the meal or glucose solution.

In a nondiabetic patient, the glucose level returns to the fasting level within to 2 hours of glucose consumption, whereas the glucose level in a diabetic patient does not return to the fasting level. A postprandial glucose level of 140 g/dL or higher suggests diabetes and warrants further testing, such as the oral glucose tolerance test.

Putting It All into Practice

My name is Michelle Villers, and I work for a physician in an internal medicine medical office. My primary job responsibility includes running the laboratory at the office. I mainly draw blood and perform blood chemistry tests. I also work up patients, run electrocardiograms, apply Holter monitors, and perform pulmonary function tests.

When performing a venipuncture, you need to make sure all the necessary equipment is on hand and ready. Sometimes you may have a tube that has no vacuum in it. In cases like these, it is always better to have a couple of spare tubes on hand. I recently had an experience in which one of my tubes had no vacuum. Luckily, I had a few extra tubes within arm’s reach, so I did not have to interrupt the procedure to get a new one. I have learned that you can never be too prepared. 

Oral Glucose Tolerance Test

The oral glucose tolerance test (OGTT) provides more detailed information about the ability of the body to metabolize glucose by assessing the insulin response to a glucose load. The OGTT is used to assist in the diagnosis of prediabetes, diabetes, gestational diabetes, hypoglycemia, and liver and adrenocortical dysfunction. It provides a more thorough analysis of glucose use than is provided by the FBG or the 2-hour PPBG test.

Testing Requirements

The patient is usually required to consume a high-carbohydrate diet, consisting of 150 g of carbohydrate per day, for 3 days before the oral glucose tolerance test. The patient must be in a fasting state when the test begins. On the morning of the test, a blood specimen is drawn from the patient for an FBG. If the FBG indicates hyperglycemia, the physician should be notified because this situation is a contraindication for the administration of a large test load of glucose.

After the FBG has been performed, the patient is instructed to drink a solution containing 75 g of glucose. At regular intervals thereafter a blood specimen is taken to determine the patient’s ability to handle the increased amount of glucose. Each blood specimen must be labeled carefully with the exact time of collection. The patient is permitted to eat and drink normally after completion of the test.

It is important that the patient adhere to certain restrictions during the test to ensure accurate results. Because food and fluid affect blood glucose levels, the patient must not eat or drink anything except water during the test. Smoking is not permitted during the test because tobacco is a stimulant that increases the blood glucose level. The patient should remain at the testing site so that he or she is present when needed for collection of blood specimens and to minimize activity. Activity affects the test results by using up glucose; the patient should remain relatively inactive during the test. Sitting and reading is an activity that would be recommended.

What Would You Do? What Would You Not Do?

Case Study 1

Crystal Louellen is at the medical office for an oral glucose tolerance test. She says that she tried not to eat anything, but she started shaking, so she stopped at McDonald’s on the way over and got a sausage biscuit and orange juice. Crystal gets quite upset when she learns that she has to come back again to have her test run. She said that she hired a babysitter to watch her four preschool-age children. She demands to know why this test takes so long and why she can’t have anything to eat before the test. Crystal wants to know if she can bring her children next time, so she doesn’t have to hire a babysitter. Crystal says that she’s a “nicotine” addict, and when she’s not needed for testing, she could take the kids outside to play. She says that way the kids won’t bother anyone and she can have a cigarette at the same time. 

Side Effects

During the test, the patient may experience some normal side effects, including weakness, a feeling of faintness, and perspiration. These are considered normal reactions of the body to a decrease in the glucose level as insulin is secreted in response to the glucose load. The patient should be reassured that this is a temporary condition. Serious symptoms of severe hypoglycemia should be reported immediately to the physician; these may include headache; pale, cold, and clammy skin; irrational speech or behavior; profuse perspiration; and fainting.

Interpretation of Results

As glucose is absorbed into the bloodstream, the blood glucose level of a nondiabetic individual increases to a peak level of 160 to 180 mg/dL approximately 30 to 60 minutes after the glucose solution is consumed. The pancreas secretes insulin to compensate for this rise, and the blood glucose returns to the fasting level within 2 hours of ingestion of the glucose solution.

The individual with diabetes does not exhibit the normal use of glucose just described. This is because individuals with diabetes are unable to remove glucose from the bloodstream at the same rate as nondiabetic individuals. The blood glucose peaks at a much higher level. In addition, blood glucose levels are above normal throughout the test because of the lack of insulin.

Two hours after the glucose solution is consumed, the test results are interpreted as follows, according to guidelines set forth by the American Diabetes Association (ADA):

139 and below	Normal
140-199 mg/dL	Prediabetes (also known as impaired glucose tolerance)
200 mg/dL or above	Diabetes (confirm by repeating the OGTT test on another day)

Hypoglycemia

Hypoglycemia is a condition in which the glucose in the blood is abnormally low (FBG below 70 mg/dL). During the OGTT, patients with this condition exhibit an abnormally low blood glucose level, beginning at the 2-hour interval and continuing for 4 or 5 hours. Hypoglycemia results from removal of glucose from the blood at an excessive rate, or from decreased secretion of glucose into the blood, which can be caused by an overdose of insulin, Addison disease, bacterial sepsis, carcinoma of the pancreas, hepatic necrosis, or hypothyroidism.

Tests for Management of Diabetes

It is important for individuals with diabetes to manage their condition effectively. This is best accomplished by keeping blood glucose levels as close to normal as possible. Diabetic patients who maintain good blood glucose control generally experience fewer symptoms and delay or prevent long-term complications of the disease; these results can lead to a longer life.

Two testing methods are used for the management of diabetes—self-monitoring of blood glucose and the hemoglobin A_1c test. Self-monitoring of blood glucose, which is performed by diabetic patients at home, measures day-to-day fluctuations in blood glucose levels. The hemoglobin A_1c test must be ordered by the physician and provides an average or overall picture of the patient’s blood glucose levels over time. These testing methods assist the patient and the physician in determining whether the diabetes management plan is working or whether it needs to be adjusted.

Self-Monitoring of Blood Glucose

Individuals with diabetes cannot usually tell by the way they feel whether or not their blood glucose levels are within normal range. The only way for them to know for certain is by self-monitoring of blood glucose (SMBG). SMBG not only provides diabetic patients with feedback for maintaining normal blood glucose levels, it also assists them in anticipating and treating day-to-day, or even hour-to-hour, fluctuations in glucose levels brought on by food, exercise, stress, and infection.

Diabetic patients who take insulin (insulin-dependent) must monitor their blood glucose levels each day. Based on the results of SMBG, decisions can be made regarding insulin and dietary adjustments that may be necessary to maintain normal glucose levels and to avoid the extremes of hypoglycemia and hyperglycemia (see Chapter 35). Satisfactory control of the blood glucose level on a day-to-day basis through SMBG reduces symptoms of the disease and helps delay or prevent long-term complications that can occur with diabetes.

Memories from Externship

Michelle Villers: During my externship experience, I was assigned to a four-physician pediatric practice. The office was constantly busy with screaming children. As if I were not nervous enough, I was asked to assist in the removal of sutures. When I walked into the room with the physician, beads of sweat began to form on my forehead. A child was lying on the examining table—a little boy no more than 7 years old. He was there to have sutures removed from a recent surgery. The sutures had been tied very well, and it was difficult for the physician to cut them. The little boy lay there with tears streaming down his cheeks. I reassured him and talked to him, and his tears began to subside. “A few more minutes and it will be all over,” I told him. And within those next few minutes, the physician cut the last suture. The little boy eagerly hopped down off the examining table and gave me a big hug. I learned that day how a little reassurance can make everyone involved feel better. 

Patient Teaching

Diabetes

Answer questions patients have about diabetes.

What is diabetes?

Diabetes is a lifelong condition that occurs when the body is not able to use glucose for energy because of a problem with insulin. Diabetes develops when the body produces little or no insulin, or when the body cannot use the insulin it does produce (known as insulin resistance). According to the American Diabetes Association, almost 24 million Americans have diabetes; of these, nearly 6 million are not yet diagnosed and are unaware that they have diabetes. An additional 57 million people have prediabetes. Prediabetes is a condition in which the glucose levels of an individual are higher than normal, but not high enough to be classified as diabetes. An individual with prediabetes has an increased risk of developing type 2 diabetes.

The cause of diabetes is not completely understood, but it seems that the predisposition to develop diabetes is inherited. Diabetes increases the risk of developing serious complications, including heart disease, blindness (retinopathy), nerve damage (neuropathy), kidney damage (nephropathy), and poor circulation, which can result in amputation of a limb.

What is the function of insulin?

Insulin is a hormone produced and secreted by the beta cells of the pancreas. The pancreas is a gland located just behind the stomach and is about the size of a hand. Insulin is required for the normal use of glucose in the body. Through the process of digestion, carbohydrates are broken down into glucose. Shortly after a meal containing carbohydrates is consumed, glucose levels in the blood begin to increase. This sends a message to the pancreas to secrete insulin. Insulin “unlocks” the cells of the body and allows glucose to enter the cells. Inside the cells, glucose is converted into energy. Glucose is the main source of energy for the body and is needed to carry out normal body functions and to assist in maintaining body temperature.

What are the symptoms of diabetes?

Individuals with diabetes produce little or no insulin or cannot use the insulin they do produce. Without insulin, glucose cannot get into the cells of the body, and it builds up in the bloodstream, resulting in a high blood glucose level, known as hyperglycemia. Although blood glucose levels are increased, the body is unable to use the glucose for energy. This results in increased hunger, weight loss, and fatigue. The body attempts to get rid of the excess glucose by expelling it in the urine. To be excreted, the glucose must be diluted in large amounts of water. This results in increased urination and increased thirst to replace the water being lost. A summary of the symptoms of diabetes follows:

• Increased urination

• Excessive thirst

• Weight loss

• Constant hunger

• Nausea and vomiting

• Abdominal pain

• Fatigue

• Blurred vision

What is the difference between type 1 diabetes and type 2 diabetes?

Two main categories of diabetes have been identified: type 1 diabetes and type 2 diabetes. Type 2 diabetes is the most common form of diabetes. Approximately 90% of individuals with diabetes have type 2 diabetes.

Type 1 Diabetes

Type 1 diabetes can occur at any age but is most apt to begin in childhood, adolescence, or early adulthood (before age 30). Type 1 diabetes is an autoimmune disease in which the body produces antibodies that attack and gradually destroy the insulin-producing beta cells of the pancreas. This results in an inability of the body to produce any insulin at all, or it may produce very little insulin. The symptoms are usually severe and occur rapidly—typically over weeks or months. Individuals with type 1 diabetes almost always require insulin therapy. The insulin is administered subcutaneously using an insulin syringe/needle or an insulin pen. An insulin pen is an insulin injection device that contains a needle and holds a vial of insulin. Insulin also can be administered through an insulin pump, which is a small, battery-operated device about the size of a cell phone that is clipped to a belt or carried in a pocket (see illustration). The pump is connected to plastic tubing that continuously delivers insulin into the subcutaneous tissue of the abdomen. An insulin pump also can be programmed to deliver varying doses of insulin as a patient’s need for insulin changes during the day (e.g., before exercise or meals).

Type 2 Diabetes

Type 2 diabetes can affect people at any age, but the chance of developing it increases with age, and it is more likely to occur in individuals who are 40 years of age or older. The biggest risk factor for developing type 2 diabetes is excess body weight. As a result of the recent increase in childhood obesity combined with a sedentary lifestyle, type 2 diabetes is starting to appear in younger age groups. Individuals with type 2 diabetes do not produce enough insulin or are not able to use the insulin they do produce (insulin resistance), resulting in high blood glucose levels. Type 2 diabetes almost always has a slow onset with mild symptoms that appear gradually over a long time (often years). Some individuals have no symptoms at all (except for high blood glucose levels). Because of this, they may be unaware that they have diabetes until a complication from prolonged hyperglycemia occurs, such as a vision problem or foot pain. Type 2 diabetes is first treated by dietary adjustments, weight reduction, and exercise. These changes sometimes can restore insulin sensitivity, even if the weight loss is modest. Approximately 20% of cases of type 2 diabetes can be managed by lifestyle changes alone. The next step, if necessary, is treatment with oral hypoglycemics, which are medications taken by mouth that stimulate the release of insulin from the pancreas, help the body use its own insulin better, or both. If this treatment is ineffective, insulin therapy becomes necessary to maintain normal or near-normal glucose levels.

Only gold members can continue reading. Log In or Register to continue

Share this:

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)

Related

Related posts:

1. Digestive System
2. Interacting with Patients
3. Scheduling Appointments
4. Specialty Examinations and Procedures: Colon Procedures, Male Reproductive Health, and Radiology and Diagnostic Imaging

Stay updated, free articles. Join our Telegram channel

Join