Pediatric Medicine: Blood Test Reference Guide

Doctors, NPs, and PAs will often order blood tests on a regular basis to monitor your health. The blood chemistry test, also known as the Complete Metabolic Profile (CMP), measures some of the most important chemicals required and produced by your body to function properly. These include blood chemicals like those produced by the liver, as well as nutritional elements such as vitamins, proteins, fats, and sugar.

A CMP can involve dozens of different tests, but the tests as ordered usually measure many chemicals. We may order only a Basic Metabolic Profile (BMP), which has just electrolytes, sugar, and kidney tests. A blood count (CBC) measures your blood cells, not chemicals in the blood. Tests may be ordered individually since some insurances such as Medicare require a specific reason for each test. Some important tests are discussed below.

LIVER

Total Protein (TP) – A rough measure of the total amount of serum protein in your body. Protein measurements can reflect not only liver disease, but nutritional state, kidney disease, and many other conditions as well. If the total protein result is abnormal, further tests must be performed to identify which protein fraction, and then which specific protein, is abnormal.

Albumin – The most abundant protein found in Blood plasma, representing 40% to 66% of the total protein in your body. Albumin keeps water inside your Blood vessels. Reduced levels of albumin may reflect a variety of conditions, including primary liver disease, increased breakdown of macromolecules resulting from tissue damage or inflammation, malnutrition, malabsorption syndromes, and renal diseases.

Globulin – Globulins are a diverse group of proteins in the Blood that grouped together represent the second most common proteins (after albumin) in the Bloodstream. Globulin is actually made up of about 60 different important proteins and is one of the components that help to fight infections. Some of the proteins in this group play an important role in Blood clotting. An elevation in the level of serum globulin can indicate the presence of cirrhosis of the liver.

ALT/SGPT (Alanine Aminotransferase) – Found mainly in the liver, the activity of this enzyme is measured in Blood plasma. Damage from alcohol, strenuous exercise, some medications, and a number of diseases can cause high test values. Elevated levels of this enzyme can be an indication of viral hepatitis and other forms of liver disease.

AST/SGOT Aspartate Aminotransferase – An increase of aspartate aminotransferase (AST, formerly referred to as “SGOT”) is found in any condition involving necrosis of hepatocytes, myocardial cells, or skeletal muscle cells. As in AST/SGPT, damage from alcohol, strenuous exercise, some medications, and a number of diseases can cause high test values. Decreased serum AST is of no known clinical significance.

Bilirubin, Total – The coloring agent in the Blood that makes the plasma (serum) part of your Blood yellow. When the bilirubin level is very high for an extended period of time, the whites of your eyes and even your skin may become yellow (jaundice). Bilirubin comes from the breakdown of old red cells in the Blood. Total bilirubin is increased most commonly in liver disease (hepatitis, malignancy, advanced cirrhosis) and due to obstruction of the biliary system (gall stones, pancreatic cancer). Severe hemolytic anemia can cause moderate increases which are almost entirely made up of the unconjugated fraction. Moderate to marked hyperbilirubinemia is seen in some neonates especially if premature and can be caused by inborn errors of bilirubin metabolism or transport in a small number of cases.

Bilirubin, Direct – A specific form of bilirubin (conjugated) that is formed in the liver and excreted in bile. Under normal conditions, very little of this form of bilirubin is found in the Blood. In liver disease, however, this form of bilirubin enters the Bloodstream so that even a slightly high level may indicate a problem with the liver cells, an obstruction of the bile ducts, or impairment of liver cell function.

Alkaline Phosphatase – An enzyme found in all body tissue, but primarily in bones, bile ducts, and in the liver. A high level may indicate bone, liver, or bile duct disease. Some drugs may also cause increased levels. Expected values are higher for those who are growing (children and pregnant women) or when damage to bones or liver has occurred or with a gallstone condition. Low values are probably not significant.

KIDNEY / Electrolytes

BUN (Blood Urea Nitrogen) – A waste product, derived from protein breakdown, produced in the liver and excreted by way of the kidneys. High values may mean that the kidneys are not working as well as they should. BUN is also elevated by Blood loss, dehydration, high protein diets, and/or strenuous exercise which may temporarily and artificially raise levels. A low BUN level may be the result of liver disease, a low protein diet, pregnancy, or drinking an extreme amount of water. Normal BUN levels should be between eight and 23 milligrams per deciliter of blood (mg/dL); normal creatinine levels should be between 0.7 and 1.3 mg/dL.

Creatinine – A waste product largely from muscle metabolism (breakdown). The concentration of creatinine in the blood depends upon the amount of muscle that you have and the ability of your kidneys to excrete creatinine. High values, especially with high BUN levels, may indicate problems with the kidneys. Because of its insensitivity in detecting early renal failure, the creatinine clearance is significantly reduced before any rise in serum creatinine occurs. The renal impairment may be due to intrinsic renal lesions, decreased perfusion of the kidney, or obstruction of the lower urinary tract. Low values are generally not considered significant.

BUN/Creatinine Ratio – By comparing the BUN level in the Blood to the creatinine level, your physician can determine if a high BUN level is caused by kidney disease, dehydration, or gastrointestinal bleeding.

Calcium – Controlled in the Blood by the parathyroid glands and the kidneys, calcium is one of the most important elements in the body. Virtually all of the calcium in your body is found in bone (99%). That other 1% is very important for proper Blood clotting, nerve, and cell and enzyme activity. The parathyroid gland is the main regulator of calcium in the body. An elevated calcium can be due to medication, inherited disorders of calcium handling in the kidneys, bone disease, or excess parathyroid gland activity or vitamin D. Low calcium can be due to malnutrition, drugs, and certain metabolic disorders and should be re-evaluated.

Sodium – An electrolyte regulated by the kidneys and adrenal glands. This element plays an important role in the water/salt balance in your body. There are numerous causes of high and low sodium levels, but the most common causes of low sodium are diuretic usage and excessive water intake in patients with heart or liver disease. A high level can be caused by an excessive intake of salt or even an insufficient intake of water. Sodium levels should be between 136 and 144 millimoles per liter of Blood (mmol/L).

Potassium – Controlled very carefully by the kidneys, potassium is an electrolyte found primarily inside cells. Its role is to maintain water balance inside the cells and to help in the transmission of nerve impulses. It is very important for the proper functioning of the nerves and muscles, particularly the heart. Any value outside the expected range, high or low, requires immediate medical evaluation. This is especially important if you are taking a diuretic (water pill) or heart pill (Digitalis, Lanoxin, etc.) A low potassium level can cause muscle weakness and heart problems. A high potassium level can be found in kidney disease or in the over ingestion of potassium supplements. Potassium levels should be between 3.6 and 5.1 mmol/L.

Chloride – Important to the function of nerves, muscles, and cells. Chloride is an electrolyte regulated by the kidneys and adrenal glands. It is usually associated with a high or low level of sodium or potassium. An increase in serum chloride is seen in dehydration, renal tubular acidosis, acute renal failure, diabetes insipidus, prolonged diarrhea, and some other rare conditions or medications. Some drugs cause decreased chloride levels. Levels should be between 99 and 108 mmol/L.

CO2– reflects the acid status of your Blood. Abnormally high or low levels may indicate severe problems if you have had prolonged vomiting, are on lots of fluid pills, or if have out-of-control diabetes. Normal values for CO2 in the blood range from 20 to 29 milliequivalents per liter (mEq/L).

HEART

Total Cholesterol – Cholesterol in itself is not all bad, in fact, our bodies need a certain amount of this substance to function properly. When the level gets too high, however, serious problems can result. Levels of 200 or more are considered too high for good health. Levels of 240 and above are considered very high risk and may indicate the need for cholesterol-lowering medication. A low-fat diet and regular exercise are recommended. As the level of blood cholesterol increases, so does the possibility of plugging the arteries due to cholesterol plaque build-up. Such a disease process is called “hardening of the arteries” or atherosclerosis. When the arteries feeding the heart become plugged, a heart attack may occur. If the arteries that go to the brain are affected, then the result is a stroke.

HDL Cholesterol – (High-Density Lipoprotein) A ‘good cholesterol’ as it protects against heart disease by helping remove excess cholesterol deposited in the arteries. High levels seem to be associated with a low incidence of coronary heart disease. The latest guidelines recommend an HDL >45. If your level is below 30, it can signal a significant risk of early heart disease.

Triglycerides – Fat carried in the Blood. Normal triglycerides should be between 50 and 200 mg/dL. Triglyceride levels over 150 mg/dl may be associated with problems other than heart disease. If levels exceed 500 mg/dL, the situation is considered acute. The ways to lower triglycerides are 1) weight reduction, if overweight; 2) reduce animal fats in the diet: eat more fish; 3) take certain medications that your physician can prescribe such as Lopid, Tricor, or Niacin; 4) get regular aerobic exercise; and, 5) decrease alcohol and sugar consumption. Alcohol and sugar are not fats, but the body can convert them into fats, then dump those fats into your Bloodstream. High triglycerides are also associated with pancreatitis.

LDL Cholesterol – (Low-Density Lipoprotein) Considered “bad cholesterol” because cholesterol deposits form in the arteries when LDL levels are high. An LDL level of less than 130 is recommended; 100 is ideal; values greater than 160 are considered high risk and should be followed up by your physician. Those persons who have established coronary or vascular disease or Diabetes may be instructed by their doctor to get their LDL Cholesterol well below 100. You should ask your doctor which LDL target he or she wants for you.

VLDL Cholesterol – (Very Low-Density Lipoprotein) A type of cholesterol found in the blood that is considered to be the most dangerous form of lipoprotein. They carry the least amount of protein and the most amount of fat. They also stick to artery walls and contribute to plaque build-up.

CK/CPK – An enzyme that is very useful for diagnosing diseases of the heart and skeletal muscle. This enzyme is the first to be elevated after a heart attack (three to four hours). If CPK is high in the absence of heart muscle injury, this is a strong indication of skeletal muscle disease. Sometimes this is checked to monitor possible muscle irritation from cholesterol-lowering drugs.

LDH – The enzyme present in all human cells. Anything that damages cells, including blood drawing itself, will raise amounts in the Blood. If Blood is not processed promptly and properly, high levels may occur. If all values except LDH are within expected ranges, it is probably a processing error and does not require further evaluation.

BONES

Calcium – Increased levels of plasma calcium may indicate the presence of malignant disease or hyperparathyroidism. Less commonly, it could reflect thyrotoxicosis, vitamin D intoxication, the use of thiazide diuretics, sarcoidosis, and other disorders. Reduced levels of calcium may reflect vitamin D deficiency, renal disease, hypoparathyroidism, magnesium deficiency, and other disorders.

Alkaline Phosphatase (ALP) – Alkaline phosphatases are a family of enzymes that are present throughout the body, but the most important places are in bone, liver, and bile ducts. Elevated levels of ALP are associated with liver and bile duct disorders and bone diseases. Growing children, because of bone growth, normally have higher levels than adults. Low values are not generally considered significant.

METABOLISM (Pancreas)

Glucose – Glucose is a chief source of energy for all living organisms. Elevated Blood glucose levels (hyperglycemia), in someone who has fasted for 12 hours, maybe an indication of diabetes mellitus if the fasting level is above 124. Lower-than-normal Blood glucose levels (hypoglycemia) may mean too much insulin in your blood, or could be caused in a variety of other ways, often transiently, and must be carefully examined under specific clinical conditions before expanding the diagnosis.

MINERALS

Iron – The body must have iron to make hemoglobin and to help transfer oxygen to the muscles. If the human body is low in iron, all body cells, particularly muscles in adults, do not function properly. Conversely, too much iron can cause injury to the heart, pancreas, joints, and genital parts in both males and females. Excess iron is found in the hereditary Blood disease called hemochromatosis.

Ferritin – Measured to assess the amount of iron, important for red Blood cell production, in the body. Ferritin is useful for the early detection of iron deficiency. Ferritin is the major iron storage protein. The serum ferritin level is directly proportional to the amount of iron stored in the body.

Magnesium – Magnesium, a Blood salt, found primarily inside the cells, helps regulate energy production in the cells and is necessary for nerve function. This test is not often ordered for adults.

Phosphorus – Phosphorus is closely associated with calcium in bone development. Most of the phosphorus in the body is found in the bones. An adequate phosphorus level in the Blood is very important for muscle and nerve function. Increased levels of plasma phosphate ion may indicate imminent renal failure, hypoparathyroidism, acromegaly, excessive phosphate intake, and vitamin D intoxication. Sharply decreased levels of plasma phosphate may reflect starvation or malnutrition, vitamin D deficiency, primary hyperparathyroidism, magnesium deficiency, and diabetic ketoacidosis.

HEMATOLOGY TESTS

These tests are the most commonly used Blood test tool to measure the number and amount of formed elements in the Blood. Formed elements include red blood cells, white blood cells, and platelets.

COMPLETE BLOOD COUNT (CBC)

Red Blood Cells (RBC) – Also called erythrocytes, RBCs are responsible for delivering oxygen throughout the body. There are between 3.6 to 6.1 million red Blood cells in a single cubic millimeter of Blood. Anemia, a condition generally defined as a decreased number of red Blood cells, can be caused by certain anti-HIV drugs or be a sign of an underlying illness. Women of child-bearing age may also experience anemia as a result of blood loss from their menstrual periods. One of the most common physical symptoms of anemia is fatigue.

Hemoglobin (HGB) – A protein that enables the RBCs to distribute oxygen throughout the body. A hemoglobin test is done when a person is ill or during a general physical examination. Good health requires an adequate amount of hemoglobin. The amount of oxygen in the body tissues depends on how much hemoglobin is in the red cells. Without enough hemoglobin, the tissues lack oxygen, and the heart and lungs must work harder to try to compensate. If the test indicates a “less than” or “greater than” normal amount of hemoglobin, the cause of the decrease or increase must be discovered. Low hemoglobin usually means the person has anemia. Anemia results from conditions that decrease the number or size of red cells, such as excessive bleeding, a dietary deficiency, destruction of cells because of a transfusion reaction or mechanical heart valve, or an abnormally formed hemoglobin. High hemoglobin may be caused by polycythemia vera, a disease in which too many red Blood cells are made. Hemoglobin levels also help determine if a person needs a Blood transfusion. Normal hemoglobin levels range from 12 to 16 grams per deciliter (g/dL) of Blood. Usually, a person’s hemoglobin must be below eight gm/dl before a transfusion is considered.

Hematocrit – Hematocrit measures the percentage of blood that is occupied by RBCs. Generally speaking, red Blood cells should make up 40% to 52% of the total Blood volume in men and 35% to 46% in women. The hematocrit is a compound measure of red Blood cell number and size.

Calculated Results (Indices) – The values that measure hemoglobin, hematocrit, and platelet components found in red Blood cells. There are five indices:

MCV – (Mean Corpuscular Volume) – Measures the average size of red Blood cells. Range: 80 to 95 femtoliter;

MCH (Mean Corpuscular Hemoglobin) – Reflects the average weight of hemoglobin found in the red Blood cell. Range: 27 to 31 pg/cell;

MCHC (Mean Corpuscular Hemoglobin Concentration) – reflects the average amount of hemoglobin in the red Blood cell. Range: 32 to 36 gm/dl;

MPV (Mean Platelet Volume) – Reflects the average volume of platelets. Range: 7.4 – 10.4 fL; and,

RDW (Red Blood Cell Distribution Width) – Reflects the distribution of the size of the red Blood cell population. Range: 2 to 8% of white Blood cells.

WHITE BLOOD CELLS – DIFFERENTIAL

Neutrophils – Neutrophilia (>25,000/µL) brings up the problem of hematologic malignancy (leukemia, myelofibrosis) versus reactive leukocytosis, including “leukemoid reactions.” Laboratory tests of this problem may include an expert review of the peripheral smear, leukocyte alkaline phosphatase, and cytogenetic analysis of peripheral Blood or marrow granulocytes. Neutropenia may be found in certain infections, including typhoid fever, brucellosis, viral illnesses, rickettsioses, and malaria. Other causes include aplastic anemia (see list of drugs above), aleukemic acute leukemias, thyroid disorders, hypopituitarism, cirrhosis, and Chediak-Higashi syndrome.

Lymphocytes – Lymphocytosis is seen in infectious mononucleosis, viral hepatitis, cytomegalovirus infection, other viral infections, pertussis, toxoplasmosis, brucellosis, TB, syphilis, lymphocytic leukemias, and lead, carbon disulfide, tetrachloroethane, and arsenical poisonings. A mature lymphocyte count >7,000/µL in an individual over 50 years of age is highly suggestive of chronic lymphocytic leukemia (CLL). Drugs increasing the lymphocyte count include aminosalicylic acid, griseofulvin, haloperidol, levodopa, niacinamide, phenytoin, and mephenytoin. Lymphopenia is a characteristic indication of AIDS. It is also seen in acute infections, Hodgkin’s Disease, systemic lupus, renal failure, carcinomatosis, and with the administration of corticosteroids, lithium, mechlorethamine, methysergide, niacin, and ionizing irradiation. Of all hematopoietic cells, lymphocytes are the most sensitive to whole-body irradiation, and their count is the first to fall in radiation sickness.

Eosinophils – Eosinophilia is seen in allergic disorders and invasive parasitoses. Other causes include pemphigus, dermatitis herpetiformis, scarlet fever, acute rheumatic fever, various myeloproliferative neoplasms, irradiation, polyarteritis nodosa, rheumatoid arthritis, sarcoidosis, tuberculosis, coccidioidomycosis, smoking, idiopathically as an inherited trait, and in the resolution phase of many acute infections. Eosinopenia is seen in the early phase of acute insults, such as shock, major pyogenic infections, trauma, surgery, etc. Drugs producing eosinopenia include corticosteroids, epinephrine, methysergide, niacin, niacinamide, and procainamide.

Basophils – Basophilia, if absolute and of marked degree, is a great clue to the presence of myeloproliferative disease as opposed to leukemoid reaction. Other causes of basophilia include allergic reactions, chickenpox, ulcerative colitis, myxedema, chronic hemolytic anemias, Hodgkin’s Disease, and status post-splenectomy. Estrogens, antithyroid drugs, and desipramine may also increase basophils.

PLATELETS

Platelets are cells in the Blood which are necessary to help Blood clot. A normal platelet count is between 150 to 440 thousand per cubic millimeter. Low platelet counts are called thrombocytopenia which can be caused by some drugs.

Pancreatic Tests – Amylase and Lipase, enzymes produced by the pancreas to aid in the digestion of carbohydrates, are strong indicators of pancreatic disease (pancreatitis) if they are elevated. Pancreatitis, if not properly dealt with, can cause serious nutritional problems and even death. Pancreatitis, diagnosed early, is most often reversible once revealed and treated. Amylase is also found in saliva, and elevated blood levels of amylase are sometimes due to leakage from the salivary glands. Further tests can be done to distinguish between these two sources of amylase.

Serology Tests: Unlike microbiological tests, which look for the presence of a disease-causing microorganism, serologic tests most often look for specific antibodies produced by the immune system in response to specific disease-causing microorganisms. Also unlike microbiology tests, serology tests are very useful to determine if the patient has been exposed to an infection before they begin showing signs of disease.

Syphilis Serology – STS or VDRL – Syphilis is a potentially fatal bacterial infection usually spread via sexual activity (i.e., vaginal, or oral, or anal sex). If detected and treated early, usually during the first year of infection, syphilis can be controlled. If left unchecked, it becomes much more difficult to treat and can result in serious disease of the brain and death. It is generally recommended that those who are sexually active be tested for syphilis antibodies at least annually. Serology testing can also be used to determine if the infection has responded effectively to therapy.

Hepatitis B and Hepatitis C Serology – Hepatitis B virus (HBV) and Hepatitis C virus (HCV) can both cause liver problems. HBV is not usually fatal but can cause liver problems in a small percentage of those infected. HCV, on the other hand, can cause serious liver disease in the majority of patients infected with the virus.

Mononucleosis – Infectious mononucleosis is a viral disease that affects certain Blood cells. It is caused by the Epstein-Barr virus (EBV), which is a member of the herpes virus family.

Epstein Barr – This test is sometimes checked to see if prolonged fevers or fatigue are caused by this difficult virus. Antibodies are checked to see if there are signs of recent or past infections. Most people develop antibodies eventually, but if the early antibodies are present, it may give us a clue to a recent infection causing symptoms.

HIV Antibody Testing – This test has remained one of the least expensive, most reliable methods of diagnosing HIV. HIV antibody testing also allows patients to find out their status many years before they get sick, allowing them to start the medication to treat HIV. Results of this test cannot be given over the phone and you must sign a form explaining the HIV test before we can send it.

OTHER TESTS: There are some tests that do not easily fit into any of the other categories. We group them together here.

Thyroid – There are two often utilized types of thyroid hormones easily measurable in the Blood, thyroxine (T4) and triiodothyronine (T3). For technical reasons, it is easier and less expensive to measure the TSH and that usually tells us what is wrong, if that is off we may also measure FreeT4 level, but T3 is usually not measured on screening tests.

Thyroid Stimulating Hormone (TSH) – This protein hormone is secreted by the pituitary gland and regulates the thyroid gland. A high level suggests your thyroid is underactive, and a low level suggests your thyroid is overactive. This is usually the test used to screen for high or low thyroid and monitor the dosage of medications such as Synthroid, Levoxyl, Unithroid, etc.

T3 Uptake or Thyroid Uptake – This test often causes confusion. This is NOT a thyroid test, rather a test on the proteins that carry the thyroid around in your bloodstream. Moreover, a high test number may indicate a low level of the protein. The method of reporting varies from lab to lab. The test is to compute the free thyroxine index.

Thyroxine (T4) – This shows the total amount of the T4. High levels may be due to hyperthyroidism, however, technical artifact occurs when estrogen levels are higher from pregnancy, birth control pills, or estrogen replacement therapy. A Free T4 (see below) can avoid this interference.

Free Thyroxine Index (FTI or T7) – A mathematical computation allows the lab to estimate the free thyroxine index from the T4 and T3 Uptake tests. The results tell us how much thyroid hormone is free in the bloodstream to work on the body. Unlike the T4 alone, it is not affected by estrogen levels.

Free T4 – This test directly measures the free T4 in the Blood rather than estimating it like the FTI. It is a more reliable, but a little more expensive test. Some labs now do the Free T4 routinely rather than the Total T4.

Total T3 – This test is usually ordered when thyroid disease is being evaluated. T3 is the stronger and shorter-lived version of thyroid hormone. Some people with high thyroid levels secrete more T3 than T4. In these (overactive) hyperthyroid cases the T4 can be normal, the T3 high, and the TSH low. The Total T3 reports the total amount of T3 in the bloodstream, including T3 bound to carrier proteins plus freely circulating T3.

Free T3 – This test measures the amount of thyroid hormone T3 that is “free” or not bound to carrier proteins.

Blood Sugar / Diabetes tests.

Glucose – This is a measure of the sugar level in your Blood. High values are associated with eating before the test, and diabetes. The normal range for fasting glucose is 60 to125 milligrams per deciliter of blood (mg/dL). According to ADA criteria, diabetes is diagnosed with a fasting plasma glucose of 126 or more. A precursor, Impaired Fasting Glucose (IFG) is defined as the reading of fasting glucose levels of 110 to 125. Sometimes a glucose tolerance test, which involves giving you a sugary drink followed by several Blood glucose tests, is necessary to properly sort out normal from IFG from diabetes.

NOTE: Variations in lab ‘normals’ exist, and Europeans tend to use a ‘two hour after eating’ definition of diabetes rather than fasting glucose. Using the European standard tends to increase the number of people who are classified as having diabetes.

Glycohemoglobin (Hemoglobin A1 or A1c, HbA1c) – Glycohemoglobin measures the amount of glucose chemically attached to your red Blood cells. Since Blood cells live about three months, it tells us your average glucose for the last six to eight weeks. A high level suggests poor diabetes control. Normal HbA1C is below 5 or so, the goal in Diabetes care is to keep it below 7. If this number is above 8 it is definitely time to change medications or treatment for your sugar.

Fructosamine is a blood test that gives us a look at average blood sugar over a 2 to 3 week period. It allows us to make changes in medication without waiting the full 3 months before we can test the HbA1C again. Sometimes this can be done on a machine n the office, other times it is sent to the lab.

Microalbinuria This is a test measured in the urine. It shows up protein much earlier than the usual urine test done with the dipstick. If this level is above normal I a diabetic, it is a sign that they should start taking a special medication to protect the kidney, called an ACE Inhibitor or alternately an ARB. Studies have shown that these medications can prevent some of the kidney damage done by diabetes.

by Dr. Anup Gokli