A blood chemistry panel is another common test used to evaluate a variety of components. Usually, it consists of about 7-25 tests. The information below is meant to provide an overview of these tests. Your doctor will counsel you regarding the results of your personal blood work and laboratory tests.
Kidney Function Tests
The creatinine blood test and blood urea nitrogen (BUN) test are used to assess kidney function in people with lupus kidney disease (nephritis).
- Creatinine: Creatinine is produced by your muscles as they breakdown creatine, a substance involved in muscle contraction. Creatinine is formed at a constant rate in the body and excreted by the kidneys, so by evaluating the amount of creatinine in your blood, your doctor can determine how efficiently your kidneys are working. Creatinine levels are measured by taking a sample of blood from your vein; then, the concentration of creatinine in your blood is compared to a standard amount for your age and sex. Increased blood creatinine levels may indicate an increase in lupus involvement of the kidney. Other conditions, such as high blood pressure or diabetes, can also cause elevated creatinine levels.
- Sometimes individuals are asked to provide a 24-hour urine sample for further assessment. The combination of blood and urine samples can be used to evaluate a creatine clearance—how effectively your kidneys filter small molecules, such as creatinine, from your blood. In addition, since creatinine is usually removed from the blood at a constant rate, blood creatinine levels can be used as a standard by which doctors can compare other urine or blood tests. Your serum (blood) creatinine level can also be combined with your age, weight, and gender to evaluate your estimated glomerular filtration rate (eGFR). Glomeruli are tiny ball-shaped structures in your kidneys that help filter blood and prevent the loss of valuable substances, such as blood cells and proteins. The eGFR is an educated estimate of the amount of blood that is filtered per minute by your glomeruli and is often used to detect kidney damage.
- Blood urea nitrogen (BUN): The BUN test measures the amount of urea nitrogen in your blood. The liver produces nitrogen in the form of ammonia (NH3) as it breaks down proteins into their constituent amino acids. From the liver, urea travels in your blood to the kidneys, which filter the urea and flush it from your body in the form of urine. To evaluate an individual’s BUN level, blood is drawn from the vein, and the concentration of urea nitrogen in the blood is evaluated and compared to a standard value for that person’s age range. Even though increased protein levels in a person’s diet can cause their blood urea nitrogen levels to increase, elevated BUN may suggest kidney involvement due to lupus or another condition such as dehydration that causes decreased blood flow to the kidneys. Low BUN levels are uncommon and are usually not as important; they can suggest certain conditions, such as malnutrition, over-hydration, or liver disease, but doctors usually use other tests to monitor these conditions.
Blood Glucose (Sugar) Test
Tests of blood glucose levels are performed to determine if an individual’s blood glucose is in normal range. This test helps to detect hyperglycemia (high blood sugar), hypoglycemia (low blood sugar), and diabetes (which can occur after long-term steroid therapy). Glucose is a simple sugar that your body gets from the food you eat. The cells of your body need glucose to obtain energy, and they cannot function without it. When we think of providing our bodies with energy, we usually think about movement and physical activity. However, glucose is also vital to the cells of your brain and central nervous system.
The amount of glucose in your blood is controlled by a feedback mechanism involving two hormones, insulin and glucagon. These hormones work to ensure that your blood contains the right amount of glucose so that your cells—including those in your brain and central nervous system—can function correctly. When your body takes in glucose after a meal, insulin is secreted by cells in your pancreas (beta cells) in order to lower your blood glucose to the appropriate level. When your blood sugar gets too low, glucagon is secreted by alpha cells of the pancreas in order to raise glucose levels. Disruptions in this feedback mechanism can be harmful to your body. In people with diabetes, the body either does not make enough insulin or does not use it properly. High or low blood sugar levels caused by diabetes or other conditions can be serious if not kept in check.
Blood glucose levels are usually evaluated when the patient is fasting, but they can also be taken at random, after a meal, or in a “challenge” test in which a person consumes a certain amount of glucose to challenge their system and track the way his/her body deals with glucose over time. Diabetics usually monitor their own blood glucose levels at home.
Fasting Lipid Profile
A lipid profile is a group of tests that includes measurements of total cholesterol, HDL-cholesterol (“good cholesterol”), LDL-cholesterol (“bad cholesterol”), and triglycerides (fats), all of which are risk factors for cardiovascular disease. It is important that your doctors perform fasting lipid profiles if your cholesterol has been elevated, because people with lupus are at an increased risk for heart disease. In fact, cardiovascular disease—not lupus itself—is the number one cause of death in people with lupus. Furthermore, medications used in lupus treatment, especially corticosteroids such as prednisone, can raise blood pressure, blood glucose, cholesterol, and triglyceride levels, exacerbating the risk factors for cardiovascular disease in people with lupus.
A fasting lipid profile is performed only when a patient is fasting (i.e., has not eaten since midnight of the previous night). Fasting ensures an accurate reading of your baseline total cholesterol, HDL, LDL, and triglyceride levels. However, please understand that it is alright to take your medications with water upon the day you are fasting—water does not affect the fasting lipid profile.
- Total Cholesterol: Cholesterol is a fatty substance made in the body and absorbed from certain foods that is essential in your body’s normal processes. It plays an important role in the membranes of your cells, is used to make hormones, and helps form the bile acids needed for your body to obtain nutrients from food. Your total cholesterol is a measurement of both types of cholesterol—LDL and HDL—and should be below 200 mg/dL. Total cholesterol levels above 240 mg/dL are considered dangerously high, especially in people with additional risk factors for cardiovascular disease, such as smoking, obesity, or family history. If your total cholesterol level is above 200 mg/dL, your doctor will most likely recommend that you follow a diet low in saturated fats and cholesterol and begin a moderate exercise regimen. If diet and exercise alone are not enough to control your cholesterol, she/he may prescribe a medication called a statin to help lower your cholesterol levels.
- Low Density Lipoproteins (LDL): Cholesterol circulates in the body in complex molecules called lipoproteins. Low density lipoproteins (LDL) are sometimes known as “bad cholesterol,” because they can deposit excess cholesterol in your arterial walls, restricting blood flow and causing a condition known as atherosclerosis. If arteries become blocked, a person can suffer heart attack, stroke, or other complications. LDL levels above 100 mg/dL are considered to be above the optimal range. If you have other risk factors for heart disease, such as a history of smoking, low HDL levels, high blood pressure, diabetes, or a personal or family history of cardiovascular disease, you should aim for lower LDL levels.
- High Density Lipoproteins (HDL): High density lipoproteins (HDL) are known as “good cholesterol” because they help to move cholesterol out of the body by carrying it to the liver where it is processed for excretion. HDL levels less than 40mg/dL are associated with an increased risk of heart disease, but a good HDL level is above 60mg/dL.
A comprehensive metabolic panel will also check the levels of certain proteins in your blood. Specifically, the test checks for albumin levels and total protein levels.
- Albumin: Albumin is a small protein made in the liver that constitutes the major protein in blood serum. Albumin performs many functions in your body, including nourishing tissues, transporting various substances through the body (hormones, vitamins, drugs, and ions), and preventing fluid from leaking out of your blood vessels. Albumin concentration will drop if a person suffers from liver damage, kidney disease, malnourishment, serious inflammation, or shock. Abumin levels allow your doctor to assess for or monitor liver or kidney disease due to lupus and other factors.
- Total Protein: In addition to albumin, your blood serum also contains a protein called globulin. In fact, globulin is actually a class of proteins that includes enzymes, antibodies, and hundreds of other proteins. A total protein test measures the combined amount of these proteins in your blood. An albumin to globulin (A/G) ratio is also computed. A person’s total protein level gives information about kidney damage, liver damage, and nutritional health. If your total protein falls outside of the normal level, your doctor will most likely order other tests to assess for liver or kidney function.
Electrolytes are ions (electrically charged chemicals) in the blood and other body fluids. The concentration of electrolytes in your body depends on adequate intake of nutrients, proper absorption of nutrients by the intestines, and proper kidney and lung function. Abnormal electrolyte concentrations can indicate abnormalities in certain organs and bodily processes. For example, retention of sodium, bicarbonate, or calcium can indicate problems with kidney function. Hormones also help to control electrolyte concentrations, so abnormal electrolyte levels can also reveal certain hormone deficiencies or problems with certain hormone-regulating glands or organs. Some of the electrolytes measured in a comprehensive metabolic panel are explained below.
- Sodium (Na+): Sodium helps to regulate your body’s water balance and plays an important role in proper heart rhythm, blood pressure, blood volume, and brain and nerve function. Hypernatremia refers to having too much sodium in the blood; this can occur, for example, due to a high-salt diet. Too much sodium in your blood can cause high blood pressure, among other things. Hyponatremia refers to having too little sodium in the blood. Hyponatremia can cause confusion, restlessness, anxiety, weakness, and muscle cramps. Sodium levels in the blood are regulated by a hormone called aldosterone that is secreted by the adrenal glands. Aldosterone works to regulate sodium levels by increasing your kidneys’ reabsorption of sodium ions.
- Potassium (K+): Potassium plays a role in regulating the acid-base chemistry and water balance in your blood and body tissues. It also helps your body to synthesize proteins and make use of carbohydrates for fuel. Potassium is essential for normal muscle growth and helps sodium and calcium to maintain normal hearth rhythm and regulate the body’s water balance. Potassium also helps your muscles to contract and your nerves to send impulses. Potassium levels may be low if an individual is on a diuretic (fluid pill) such as hydrochlorothiazide (HCTC) or furosemide (Lasix). Blood potassium levels that are too high or low may lead to muscle weakness and cramping; very low levels may cause irregularities in heartbeat. Like sodium levels, potassium levels in the blood are regulated by aldosterone, which promotes potassium loss from your kidneys.
- Calcium (Ca2+): Most people recognize calcium as a part of bones and teeth, but calcium plays many other roles in the body, such as regulating heartbeat, transmitting nerve impulses, contracting muscles, and helping blood to clot properly. Blood calcium levels are regulated by parathyroid hormone, which is secreted by the parathyroid gland, and calcitonin, which is secreted by the thyroid gland. Since lupus causes an increased risk of osteoporosis and corticosteroid (e.g., prednisone) use can elevate this risk, most people with lupus should take calcium and vitamin D supplements to help maintain adequate bone density. Medications called bisphosponates may be added to help with bone integrity if osteoporosis is detected. However, it is important that you realize that a blood calcium test measures the amount of calcium in the blood, not the bones. For an adequate measurement of bone health, you will need to obtain a DEXA scan every 2 years.
- Chloride (Cl-): Chloride ions help your body in maintaining proper pH and fluid balance. It also secreted by the stomach during digestion. Excessive sweating, vomiting, or diarrhea can cause chloride levels to drop. Low chloride levels may alter the pH of your blood, cause dehydration; they may also cause you to lose potassium.
- Carbon dioxide (CO2): This test measures the amount of carbon dioxide (CO2) in the blood, which is present in the form of CO2, bicarbonate (HCO3-), and carbonic acid (H2CO3). These three forms are involved in the equilibrium that maintains the pH of your blood (7.35-7.45). Bicarbonate also works with other electrolytes to maintain a certain charge balance in your cells. The concentration of carbon dioxide in your blood is maintained by your lungs and kidneys. High or low levels of CO2 may prompt your doctor to order other tests to check your kidney and lung function, blood gases, or fluid retention.
Lupus and some of the medications used to treat lupus can affect the liver. In addition, factors such as excessive alcohol intake or viral hepatitis can affect the liver in people with lupus, just as they can in the normal population. Certain tests can be performed as part of a comprehensive metabolic panel to give insight into the function of your liver. In addition, your doctor may order a test called a liver panel if she/he suspects that you have symptoms of a liver disorder. Usually these tests measure certain liver enzymes, namely alkaline phosphatase (ALP), alanine amino transferase (ALT), and aspartate amino transferase (AST). Bilirubin, a waste product of the liver that is stored in the gall bladder, is also measured. These values can be used by your doctor as a screening or monitoring tool for liver involvement. About 30-60% of lupus patients experience abnormal liver function tests; some have no symptoms of liver disorder. Generally, increased levels correlate with increased activity, but other factors can contribute to elevated levels of liver enzymes in the blood. For example, NSAIDs, acetaminophen (Tylenol), and aspirin can cause liver enzyme values to increase, especially in people with lupus. If your doctor notices abnormal liver enzyme levels, she/he may ask you to undergo additional tests for hepatitis.
The liver enzymes and substances detected in a comprehensive metabolic panel are explained in more detail below.
- Alkaline phosphatase (ALP): Alkaline phosphatase (ALP) is an enzyme—a protein that helps to bring about chemical reactions in your body—found mainly in your liver and bones. High levels of ALP in the blood may indicate bone or liver abnormalities. If high ALP values are accompanied by high values of other liver enzymes and bilirubin, then the test suggests liver involvement. Certain ratios of liver enzymes can also indicate more specific conditions. Children usually have higher ALP levels than adults because their bones are still growing.
- Alanine amino transferase (ALT): Alanine amino transferase (ALT) is another enzyme found mainly in the liver. Smaller quantities can also be found in your kidneys, heart, and muscles. Levels of this enzyme are usually assessed in conjunction with readings for other liver enzymes to determine or monitor liver involvement. Very high levels of ALT may indicate acute hepatitis.
- Aspartate amino transferase (AST): Aspartame amino transferase (AST) is an enzyme found mainly in the liver, heart, and muscles. AST is released into the blood by injured liver or muscle cells but is used primarily to detect liver damage. [Another enzyme called creatine kinase (CK or CPK) is a better indicator of heart or muscle damage.] Levels of AST are usually viewed alongside other liver enzymes to assess for liver damage. Like ALT, very high levels of AST may suggest acute hepatitis.
- Bilirubin: Bilirubin is a yellow-brown substance formed when the liver breaks down old red blood cells. Too much bilirubin can be a sign that the liver cannot adequately remove bilirubin from the system due to blockage (e.g., gallstones, tumors), cirrhosis, or acute hepatitis. Elevated bilirubin can also indicate hemolytic anemia, a reduction in red blood cells due to abnormal breakdown of red blood cells (hemolysis). Hemolytic anemia can be inherited or acquired; about 10-15% of people with lupus develop autoimmune hemolytic anemia. Hemolytic anemia causes red blood cells to have a shortened lifespan in the blood, and since bilirubin is a product of old red blood cells, it accumulates in the body faster than it can be eliminated. [Other tests called the Coombs test, haptoglobin count, and reticulocyte count are better diagnostic tests for hemolytic anemia.] Several inherited conditions, such as Gilbert’s syndrome, can also cause a person to have too much bilirubin. These conditions may be serious or benign. Often a buildup of bilirbubin is accompanied by a yellowing of the skin called jaundice.
The thyroid is a gland in your neck associated with your metabolism—the processes by which your body makes use of energy. Autoimmune thyroid disease can occur in people with lupus, as can other thyroid conditions. Usually, thyroid conditions cause the gland to release too much or too little hormone. Your doctor may order tests to detect the level of thyroid hormones in the blood, especially if you experience significant weight loss or gain, sweating, acute sensitivity to hot or cold, fatigue, or other symptoms. These tests can also help your doctor monitor the effectiveness of thyroid treatment. Tests for thyroid hormones are explained below in greater detail. Your doctor may request additional tests, such as tests for thyroid antibodies, to learn more about your condition.
- Thyroid stimulating hormone (TSH): Thyroid stimulating hormone (TSH) is a hormone released by the pituitary gland that signals the thyroid to release its hormones (T3 and T4) when levels in the blood get low. Together, TSH, T3, and T4 are part of a negative feedback loop that keeps levels of thyroid hormones constant in the blood. Abnormal levels of TSH in the blood can suggest a problem with the pituitary gland, such as a tumor, but this is unlikely. More often, high or low TSH levels indicate problems with the thyroid gland. The thyroid may not be responding to stimulation by TSH, or it may be releasing too much T3 and T4. Underactive thyroid (hypothyroidism) is more common in lupus, but overactive thyroid (hyperthyroidism) can also occur. Both of these conditions can be dangerous if not properly treated.
- T4 and T3: Thyroid hormone contains thyroxine (T4, 90%) and triidothyronine (T3, 10%). The primary role of these substances is to regulate your body’s metabolism. Abnormal levels of thyroid hormone can indicate hypo- or hyperthyroidism.
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- “BUN.” Lab Tests Online. 8 April 2009. American Association for Clinical Chemistry. 12 July 2009 <http://labtestsonline.org/understanding/analytes/bun/test.html>.
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- “Electrolytes.” Lab Tests Online. 8 April 2009. American Association for Clinical Chemistry. 12 July 2009<http://labtestsonline.org/understanding/analytes/electrolytes/test.html>.
- “Glucose.” Lab Tests Online. 8 April 2009. American Association for Clinical Chemistry. 12 July 2009 <http://labtestsonline.org/understanding/analytes/glucose/test.html>.
- “Lipid Profile.” Lab Tests Online. 18 June 2009. American Association for Clinical Chemistry. 12 July 2009 <http://labtestsonline.org/understanding/analytes/lipid/glance.html>.
- “Liver Panel.” Lab Tests Online. 8 April 2009. American Association for Clinical Chemistry. 12 July 2009 <http://labtestsonline.org/understanding/analytes/liver_panel/glance.html>.
- Parker, Janet, ed. The Encyclopedic Atlas of the Human Body: A Visual Guide to the Human Body. Chicago: Global Book, 2007.
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- “Total Protein and A/G Ratio.” Lab Tests Online. 16 May 2009. American Association for Clinical Chemistry. 12 July 2009 <http://labtestsonline.org/understanding/analytes/tp/test.html>.
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