Laboratory Tests Chapter 15

Blood Tests Obtaining Specimens Phlebotomy is the puncture of a vein for the purpose of drawing blood. This is also known as venipuncture. A Phlebotomist is an individual trained and skilled phlebotomy. A capillary puncture is the technique used when only a small amount of blood is needed as a specimen for a blood test. Named for where it is performed, it may be a fingerstick, heelstick, or earlobe stick.

Blood Tests A complete blood cell count (CBC) is a series of tests performed as a group to evaluate several blood conditions. Erythrocyte sedimentation rate, also known as sed rate, is a test based on the rate at which the red blood cells separate from the plasma and settle to the bottom of the container. An elevated count indicates the presence of inflammation in the body. A hematocrit test measures the percentage by volume of packed red blood cells in a whole blood sample. This test is used to diagnose abnormal states of hydration, polycythemia (excess red blood cells), and anemia (deficient red blood cells). A platelet count (PLC) measures the number of platelets in a specified amount of blood. This test is used to assess the effects of chemotherapy and radiation therapy and to aid in the diagnosis of thrombocytopenia (an abnormal decrease in the number of platelets) A red blood cell (RBC) count is a determination of the number of erythrocytes in the blood. A depressed count may indicate anemia or a hemorrhage lasting more than 24 hours.

Blood Tests continued A total hemoglobin (Hb) test measures the amount of hemoglobin found in whole blood. Test results measure the severity of anemia or polycythemia and monitor the response to therapy. A white blood cell (WBC) count is a determination of the number of leukocytes in the blood. An elevated count may be an indication of infection or inflammation. A white blood cell differential determines what percentage of the total WBC count is composed of each of the five types of leukocyte. This test provides information about the patient’s immune system, detects certain types of leukemia, and determines the severity of infection.

Additional Blood Tests Agglutination testing includes a variety of tests that involve the clumping together of cells or particles when mixed with incompatible serum. These tests are performed to determine the patient’s blood type and to check compatibility of donor and recipient blood before a transfusion. Blood urea nitrogen (BUN) is the amount of urea present in the blood. Urea is the major end product of protein metabolism found in urine and blood, and this test is a rough indicator of kidney function. Lipid tests, also known as a lipid panel, measure the amounts of total cholesterol, high-density lipoprotein (HDL), low-density lipoprotein (LDL) and triglycerides in a blood sample. Prothrombin time also know as pro time, is a test used to diagnose conditions associated with abnormal bleeding and to monitor anticoagulant therapy.

Additional Blood Tests continued Serum enzyme tests are used to measure the blood enzymes. These tests are useful as evidence of a myocardial infarction. The serum bilirubin test measures how well red blood cells are being broken down. Elevated levels of bilirubin, which cause jaundice, and may indicate liver problems or gallstones. A thyroid-stimulating hormone assay measures circulating blood levels of thyroid-stimulating hormone (TSH) that may indicate abnormal thyroid activity.

Urinalysis

Urinalysis is the exam of the physical and chemical properties of urine to determine the presence of abnormal elements. Routine urinalysis is performed to screen for urinary and systemic disorders. For routine analysis, a dipstick is used. Chemicals impregnated on this plastic strip react with substances in the urine and change color when abnormalities are present. More detailed testing requires microscopic examination. The average normal pH range of urine is from 4.5 to 8.0. A pH value below 7 indicates acid urine and is an indication of acidosis. A pH value above 7 indicates alkaline urine and may indicate condition including a urinary tract infection. (The abbreviation pH describes the degree of acidity or alkalinity of a substance. A pH of 7 is neutral-that is, neither acid nor alkaline. Maximum acidity is 0 pH, and maximum alkalinity is pH 14.) The specific gravity reflects the amount of wastes, minerals, and solids in the urine. Low specific gravity (dilute urine) is characteristic of diabetes insipidus. High specific gravity (concentrated urine) occurs in conditions such as dehydration, liver failure, and shock.

Conditions ID’d through Urinalysis Acetone, which has a sweet fruity odor, is found in small quantities in normal urine and in larger amount in diabetic urine. Albuminuria is the presence of the serum protein albumin in the urine and is a sign of impaired kidney function. Bacteriuria is the presence of bacteria in the urine. Calciuria is the presence of calcium in the urine. Abnormally high levels may be diagnostic for hyperparathyroidism. Lower than normal levels may indicate osteomalacia. Creatinuria is an increased concentration of creatine in the urine. Creatinine, a waste product of muscle metabolism, is normally removed by the kidneys. Its presence in urine is an indication of increased muscle breakdown or a disruption of kidney function.

Conditions ID’d through Urinalysis continued Glycosuria is the presence of glucose in the urine and is most commonly caused by diabetes. Hematuria is the presence of blood in the urine. This condition may be caused by kidney stones, infection, damage to the kidney, or bladder cancer. In gross hematuria the urine may look pink, brown, or bright red, and the presence of blood can be detected without magnification. In microscopic hematuria the urine is clear, but blood cells can be seen under a microscope. Ketonuria is the presence of ketones in the urine. Ketones are formed when the body breaks down fat. Their presence in urine may indicate starvation or uncontrolled diabetes.

Conditions ID’d through Urinalysis continued Proteinuria is an excess of serum protein in the urine and is usually a sign of kidney disease. Pyuria is the presence of pus in the urine. Urine culture and sensitivity is an additional laboratory test to identify the cause of a urinary tract infection and to determine which antibiotic would be the most effective treatment.