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Understanding your labs

October 3, 2014

BMP. CMP. CBC. LDL and HDL. TSH. Who knew our blood is like a virtual alphabet soup! Here's a short primer on what your blood test results mean and what those letters stand for. When reporting lab tests, the laboratory typically provides the name of the test followed by the lab value, followed by a reference range that represents “normal” values that are in brackets. These tests are routinely ordered and performed as panels with anywhere from 2-20 values. For any one panel, it is not unusual to see one value that is slightly out of the normal range. Unless we notify you, this is not generally cause for concern.

The Basic Metabolic Panel 
The basic metabolic panel (BMP) provides information about your body’s metabolism and includes blood chemistries (electrolytes and acid/base balance), blood sugar, and tests of kidney function. It includes 8 specific tests:

  • Calcium (Ca): measures calcium in your blood; blood calcium does not represent the level of calcium in bones and cannot assess bone health
  • Glucose (Glu): blood sugar
  • Sodium (Na): the main electrolyte in the body is sodium, and it regulates total body water
  • Potassium (K): critical to muscle and nerve functioning
  • Carbon Dioxide or Bicarbonate (CO2): represents acid-base balance in the body
  • Chloride (Cl): another electrolyte that regulates body water
  • Blood Urea Nitrogen (BUN): helps assess kidney function and to determine if an individual is dehydrated
  • Creatinine (Cr): a normal product of muscle metabolism, creatinine is used to monitor kidney function

The BPM is often ordered in emergency rooms and for hospitalized patients. It is also ordered routinely in patients with certain medical conditions such as hypertension, and may be ordered as part of your routine annual exam.

The Comprehensive Metabolic Panel 
comprehensive metabolic panel (CMP) adds liver evaluation and blood proteins to the basic metabolic panel. It adds and tests:

  • Alkaline Phosphatase (Alk Phos): used to assess injury to the gall bladder or bile ducts
  • Alanine Amino Transferase (ALT, also called SGPT): measures liver damage
  • Aspartate Amino Transferase (AST, also called SGOT): measures liver damage
  • Bilirubin (Bili, sometimes reported as ‘total’ and ‘direct’): used to monitor the liver’s filtering capabilities or to assess blockage of the bile ducts
  • Albumin (Alb): a key blood protein that helps regulate blood volume; it is also used to monitor the liver’s synthetic ability and a patient’s nutritional status
  • Total Protein (TP): a measure of albumin plus all of the other proteins in the blood The CMP is often ordered to check for diabetes, liver and/or kidney disease.

It may be routinely ordered to monitor certain health conditions, or ordered to monitor patients taking certain medications. The CMP is often ordered at the time of your annual exam with us.

The Complete Blood Count
The Complete Blood Count (CBC) analyzes blood cells – white blood cells (WBC) which fight infection, red blood cells (RBC) which carry oxygen, and platelets which help form blood clots.

A CBC is commonly used to evaluate anemia or infection. It may also help to diagnose other diseases such as leukemia, sickle cell disease or malaria, or it can be used to investigate abnormal bleeding or clotting. These tests are frequently ordered as a matter of routine for screening purposes. A few important points:

  • White blood cell (WBC): White blood cells are generally reported as thousands of WBCs in a microliter of blood - for example 5,000/µL. WBC can be high due to infection or low due to certain bone marrow diseases.
  • White blood cell differential looks at the types of white blood cells present and the percentage of each type. These include: neutrophils, lymphocytes, monocytes, eosinophils, and basophils. Different conditions can cause an increase or decrease in the types of WBC’s present.
  • Red blood cell (RBC): RBCs are reported as millions in a microliter of blood - 4,250,000/µL or 4.25x106/µL. This test is most commonly used to check for anemia.
  • Hemoglobin (HGB) measures the amount of oxygen-carrying protein in the blood. It is also used to check for anemia.
  • Hematocrit (HCT) represents red blood cells as a percentage of total blood volume. This is another test that checks for anemia.
  • The platelet count (PLT) is reported as thousands in a microliter of blood - 150,000/µL or 150.0x103/µL. Both increases and decreases can point to abnormal conditions of excess bleeding or clotting.
  • Mean platelet volume (MPV) measures the average size of your platelets. New platelets are larger, and an increased MPV occurs when increased numbers of platelets are being produced. MPV gives your doctor information about platelet production in your bone marrow.
  • Mean corpuscular volume (MCV) is a measurement of the average size of your red blood cells (RBC). The MCV is elevated when your red blood cells are larger than normal, for example in anemia caused by vitamin B12 or folate deficiency. When the MCV is decreased, your red blood cells are smaller than normal, such as is seen in iron deficiency anemia.
  • Mean corpuscular hemoglobin (MCH) is a calculation of the amount of oxygen-carrying hemoglobin inside your red blood cells. The interpretation is similar to MCV.
  • Mean corpuscular hemoglobin concentration (MCHC) is a calculation of the percentage of hemoglobin in the red blood cells. The interpretation is similar to MCV.
  • Red cell distribution width (RDW) is a calculation of the variation in the size of your red blood cells. In some anemias, the amount of variation in red blood cell size may help your doctor to evaluate the severity of your condition.

Thyroid Tests 
The thyroid is a small, butterfly-shaped gland in your neck situated just below the Adam's apple. The thyroid's role is to produce thyroid hormone which is important in controlling the body's overall metabolism. There are two types of thyroid hormone – thyroxine (or T4) and triiodothyronine (or T3).

The production of thyroid hormones by the thyroid gland is controlled by the pituitary gland in the brain. The pituitary gland produces thyroid stimulating hormone (TSH) which in turn tells the thyroid to make thyroid hormone. If the pituitary senses that the body's metabolism needs to be higher, it produces more TSH. If the pituitary senses that the body's metabolism needs to be lowered, it produces less TSH.

The pituitary's monitoring of the body's metabolism and the effect of thyroid hormone on the body's cells to change metabolism are extremely complicated. Because of its effect on body metabolism, people frequently want to explain obesity and feelings of lethargy or fatigue on thyroid deficiency. However, these conditions are rarely due to thyroid deficiency and much more commonly due to lifestyle habits and/or various psychosocial stressors.

Millions of Americans have some form of thyroid disease. Hyperthyroidism means that you have too much thyroid hormone which makes your body use energy faster than it should. Hypothyroidism means that you have too little thyroid hormone which makes your body use energy more slowly than it should.

Other common thyroid diseases include thyroiditis and goiters. Thyroiditis means that your thyroid is inflamed. Symptoms may include fever and pain, but it can also occur as subtle findings of hypo- or hyperthyroidism. A thyroid goiter is a dramatic enlargement of the thyroid gland. This rarely happens in developed countries because we supplement salt with iodine, and iodine deficiency is the most common cause of goiters.

The most commonly used first test to detect a problem with your thyroid gland is a TSH (thyroid stimulating hormone) test. It is ordered to diagnose thyroid disorders, but also ordered to screen newborns for an underactive thyroid, and to monitor thyroid replacement therapy. If your TSH level is abnormal, a free T4 (thyroxine) and free T3 (triiodothyronine) will generally be checked as well.

Because the symptoms of thyroid problems are frequently very vague, we will order a TSH as a screening test when symptoms might resemble those of a thyroid condition. For instance, signs of hypothyroidism include fatigue, weight gain, cold intolerance, and skin dryness. Signs of hyperthyroidism include fatigue, weight loss, heat intolerance, and nervousness.

The Lipid Panel 
A lipid panel or lipid profile examines various types of fats, or lipids, in the blood. Fats exist in many forms such as cholesterol and triglycerides. Cholesterol and other fats generally circulate around in the blood not as individual molecules, but in very small packages of fatty materials. These packages can take a number of different forms having different functions. The forms that you are most familiar with are LDL (low density lipoproteins) and HDL (high density lipoproteins).

LDL is the so-called “bad cholesterol” with higher levels being associated with higher degrees of coronary artery disease and other vascular disease. HDL is the so-called “good cholesterol” with higher levels being associated with lower rates of coronary and other vascular disease. The individual levels of LDL and HDL are more important than the total cholesterol as an indicator of risk of heart attacks and strokes.

Triglycerides are another form of fats and the total triglyceride level is another indicator for heart and other vascular disease. The higher your level is, the higher your risk.

We use the lipid panel to help evaluate an individual's risk of a heart attack or stroke caused by blockage of the blood vessels, or hardening of the arteries. While cholesterol is affected by personal lifestyle factors such as diet and exercise, a great deal of it is genetic. For some individuals, genetic predisposition is so strong that try as they might to lower their cholesterol with lifestyle changes, medications may ultimately be required to achieve effective control.

The lipid panel includes total cholesterol, HDL (good cholesterol), LDL (bad cholesterol), and triglycerides. Sometimes the report will also include other values such as HDL/Cholesterol ratio and a VLDL (very low density lipoprotein).

Target LDL values are:

  • High risk category: LDL less than 100 mg/dL
  • Moderate risk category: LDL less than 130 mg/dL
  • Low risk category: LDL less than 160 mg/dL

For all patients in all risk categories, HDL target is always greater than 40 mg/dL. The triglyceride target is less than 150 mg/dL. Generally, we consider treatment with medication only for patients with triglycerides over 200.

The lipid profile is used to guide clinicians in deciding how a person should be treated. The results of the lipid profile are considered along with other known risk factors of heart disease to develop a plan of treatment and follow-up. Treatment is based on your overall risk of coronary heart disease.

The first step in treating high LDL, high triglycerides, or a low HDL are lifestyle changes including a diet low in saturated fat and participating in moderate exercise. If these measures do not adequately lower your LDL-cholesterol to the target value, medication treatment should be considered. There are several classes of drugs that are effective in lowering LDL, lowering triglycerides, and raising HDL. On occasion, more than one medication will be required.

As always, we want you to know as much about your health as possible and that includes understanding your lab results. Should you have additional questions or concerns your GreenField clinician is your best resource.