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Medical Lab Tests to Diagnose Medical Problems

written by: Leigh A. Zaykoski•edited by: Leigh A. Zaykoski•updated: 5/23/2011

Medical lab tests on the blood and urine help doctors diagnose disorders that affect every system of the body. Performed by trained laboratory professionals, test samples require careful handling and processing to ensure accurate results.

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    Complete Blood Count

    The CBC blood test, also known as the complete blood count, examines the many parts of the blood to identify abnormalities. The components of this test include white blood cells count, white blood cell differential, platelet count, red blood cell count, hemoglobin, mean corpuscular volume (MCV), hematocrit, mean corpuscular hemoglobin concentration, red cell distribution width and mean corpuscular hemoglobin. The white and red blood cell counts determine the number of these cells in the blood. White blood cell counts increase in cases of cancer, inflammation and infection, and decrease in the presence of bone marrow failure, autoimmune disorders and congenital marrow aplasia. Red blood cell counts decrease in cases of anemia and increase during periods of fluid loss.

    Platelets stick together to help the blood clot after an injury. The number of platelets in the blood decreases due to severe bleeding or decreased platelet production. Decreased platelet counts also occur in cases of lupus, leukemia and hypersplenism. Hemoglobin, a protein, carries oxygen from to the cells of the body. The amount of hemoglobin in the blood decreases because of anemia. The other components of this test describe the width or volume of each type of blood cell.

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    Thyroid Panel

    Available information on thyroid laboratory tests indicates that a thyroid panel consists of tests for TSH, FT3, FT4, T3, T4 and rT3. TSH refers to thyroid stimulating hormone, a hormone released by the pituitary gland. This hormone plays a role in the secretion of T3 and T4 hormones. T3, also known as triiodothyronine, is the most active thyroid hormone. The body produces this hormone after converting T4 in the liver and thyroid tissues. FT3, or free T3, refers to the amount of T3 hormone not attached to proteins in the blood. T4 refers to tetraiodothyronine, a less active form of thyroid hormone. Most of this hormone binds to blood proteins, but some circulates freely in the blood. FT4, or free T4, refers to the amount of T4 that circulates freely in the circulatory system. Reverse T3 checks the amount of inactive T3 in the blood. In cases of hypothyroidism, some patients have high levels of reverse T3.

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    Lipid Panel

    The lipid panel measures the amount of fatty acids and lipids in the blood. While the body needs these substances for normal functioning, high levels increase the risk for heart disease and other medical conditions. The medical lab tests in this panel include HDL (high-density lipoprotein), LDL (low-density lipoprotein), triglycerides and total cholesterol. Some lipid panels also include an LDL to HDL ratio or a total cholesterol to HDL ratio, which gives doctors additional information about cholesterol levels. Total cholesterol should be less than 200 mg/dL, according to the American Heart Association. Doctors consider triglyceride levels of less than 150 mg/dL as normal.

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    Basic Metabolic Panel

    The basic metabolic blood panel, or BMP blood test, checks the levels of electrolytes in the blood. This test also determines if levels of blood urea nitrogen (BUN) and creatinine are abnormal. The body produces these substances during the breakdown of protein and normally excretes them in the urine. When kidney function declines, BUN and creatinine build up in the blood. The other medical lab tests involved in the basic metabolic panel include glucose, calcium, carbon dioxide, chloride, sodium and potassium.

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    Comprehensive Metabolic Panel

    The comprehensive metabolic panel, or CMP blood test, contains the same components as the basic metabolic panel, as well as tests that check how well the liver is functioning. In addition to the eight components of the BMP blood test, this test checks the amounts of liver enzymes and certain proteins in the blood. The substances tested with this test include alkaline phosphatase, albumin, aspartate aminotransferase (AST), alanine transaminase (ALT), direct bilirubin, total bilirubin, uric acid, lactate dehydrogenase (LDH) and gamma-GT.

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    Urinalysis, one of the most common medical lab tests, involves both macroscopic and microscopic examinations of a urine sample. The macroscopic portion of this test involves observing the sample and noting its color, clarity and volume. The first step of the chemical analysis involves checking the pH of the urine. University of Utah Health Care reports that normal urine pH ranges from 4.5 to 8.0. The test for specific gravity determines urine density, or the concentration of the urine. The urinalysis also checks for protein, glucose, ketones, nitrite and leukocyte esterase. High amounts of protein in the urine indicate kidney dysfunction. High glucose levels indicate diabetes. Ketones appear in the urine during periods of starvation or during diabetic ketoacidosis. High bacteria levels in the urine may cause increased nitrite levels. Leukocyte esterase may also indicate the presence of an infection. The microscopic examination of the urine sample checks for white blood cells, red blood cells and urinary casts.

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    Lab Tests Online: Complete Blood Count

    Meridian Valley Lab: Thyroid Panels

    WebMD: Lipid Panel Topic Overview

    American Heart Association: What Your Cholesterol Levels Mean

    Rush University Medical Center: Basic Metabolic Panel

    MedlinePlus: Comprehensive Metabolic Panel

    University of Utah Health Care: Urinalysis