Clinical Laboratory Testing – Basic Clinical Chemistry
Presentation lecture by:Cecile Sanders, M.Ed., MT(ASCP),
CLS (NCA)
Purpose of Clinical Chemistry Tests
*Measure levels of substances found normally in human blood that have biological functions. Examples: Glucose, Calcium
*Detect or measure non-functional metabolites or waste products. Examples: Creatinine, Blood Urea Nitrogen (BUN)
Clinical Laboratory Testing - Basic Clinical Chemistry
*Detect or measure substances that indicate cell damage or disease. Examples: Liver enzymes, such as ALT, Cardiac enzymes, such as CK-MB
*Detect or measure drugs or toxic substances. Examples: Dilantin, Drugs of abuse screen
* Types of Specimens for Chemical Analysis
*Whole blood, serum or plasma. The most common specimen is serum, collected in a tube with no anticoagulant so that the blood will clot.
*Urine – often 24 hour collections
*Others – Cerebrospinal Spinal Fluid (CSF) and other fluids
* Collection and Handling of Blood Specimens for Chemical Analysis
*Blood collection tubes for obtaining serum - Serum Separator Tubes (SST) do not have an anticoagulant but do contain a gel substance which will form an interface between the clot and the serum when the blood specimen is centrifuged. These tubes are sometimes referred to as “Tiger Tops”.
*Blood collection tubes for obtaining plasma
*Patient preparation; time of collection; & effects of eating on chemistry analysis
*Some specimens are increased or decreased after eating (ex. Glucose, triglycerides), so it is important to know what the test and collection method call for. Specimens for these tests are usually collected in a fasting state.
*Sometimes serum or plasma appears lipemia (milky) after a patient has eaten a fatty meal. Lipemia affects most chemistry analyses. The blood must be recollected when the patient is fasting.
* Clinical Chemistry Tests
*Normal or Reference Values – range of values for a particular chemistry test from healthy individuals
*Chemistry Panel grouping – some tests are “bundled” according to the system or organ targeted. Examples: thyroid panel, liver panel, cardiac panel, kidney panel, basic metabolic panel, etc.
* Commonly Performed Chemistry Tests or Analytes
*Proteins – essential components of cells and body fluids. Some made by body, others acquired from diet. Provides information about state of hydration, nutrition and liver function, since most serum proteins are made in the liver.
*Electrolytes – sometimes called “lytes”
*Includes sodium (Na), potassium (K), chloride (Cl) and bicarbonate (HCO3-)
*Collectively these have a great effect on hydration, acid-base balance and osmotic pressure as well as pH and heart and muscle contraction
*Levels differ depending on if inside vs. outside cells
*Important in transport of substances into and out of cells
*Minerals
*Calcium
*Used in coagulation and muscle contraction
*99% is in skeleton and is not metabolically active
*Influenced by vitamin D, parathyroid hormone, estrogen and calcitonin
*Hypercalcemia – occurs in parathyroidism, bone malignancies, hormone disorders, excessive vitamin D, and acidosis; may cause kidney stones
*Hypocalcemia – can cause tetany; occurs in hypoparathyroidism, vitamin D deficiency, poor dietary absorption and kidney disease
*Phosphorus
*80% in bone and rest in energy compounds such as ATP
*Influenced by calcium and certain hormones
*Iron
*Essential for hemoglobin
*Deficiency results in anemia; may be caused by lack of iron in diet, poor absorption, poor release of stored iron or loss due to bleeding
*Increased in hemolytic anemia, increased iron intake or blocked synthesis of iron-containing compounds, such as in lead poisoning
*Kidney Function Tests
*Serum Creatinine
*Best test for overall kidney function; not affected by diet or hormone levels
*Waste product of muscle metabolism
*Serum creatinine rises when kidney function is impaired
*BUN (Blood Urea Nitrogen)
*BUN is surplus amino acids that are converted to urea and excreted by kidneys as a waste product
*BUN influenced by diet and hormones, so it is NOT as good an indicator of renal function as serum creatinine levels
*BUN increased in kidney disease, high protein diet, and after administration of steroids
*BUN decreased in starvation, pregnancy and in persons on a low protein diet
*Uric Acid
*Formed from breakdown of nucleic acids and excreted as a waste product by kidneys
*Increased in kidney disease, but most often used to diagnosis gout (pain in joints, mainly big toe, due to precipitated uric acid crystals)
*Also increased in increased cell destruction, such as after massive radiation or chemotherapy
*Liver Function Tests
*Liver functions:
*Synthesizes glycogen from glucose
*Makes plasma proteins (albumin, lipoproteins, coagulation proteins)
*Forms cholesterol and degrades it into bile acids, which emulsifies fats for absorption
*Stores iron, glycogen, vitamins and other substances
*Destroys old blood cells and recycles components of hemoglobin
*Total Bilirubin
*Waste production of hemoglobin breakdown
*Increased in excessive RBC breakdown, such as hemolytic anemia, or impaired liver function or some sort of obstruction, such as a tumor or gall stone
*Liver Enzymes – levels increase following damage to liver tissues
*Alkaline Phosphatase (ALP or AP) - Greatly increased in liver tumors and lesions; moderately increased in diseases such as hepatitis
*Alanine Aminotransferase (ALT; formerly called SGPT) - Increases up to 10x in cirrhosis, infections or tumors and up to 100x in viral or toxic hepatitis
*Asparate Aminotransferase (AST; formerly called SGOT) - Increased in liver disease, but also in heart attacks
*Gamma Glutamyl Transferase (GGT) - Often used to monitor patients recovering from hepatitis and cirrhosis
*Lactate Dehydrogenase (LD) - Increased in liver disease and following heart attacks
*Cardiac Function Tests
*Creatine Kinase (CK) - Widely used to diagnosis and monitor heart attacks
*Troponins
* Only present in heart muscle, making it a more accurate indicator of heart attack than CK
* Cardiac Troponin T (cTnT)
* Cardiac Troponin I (cTnI)
*Lipid Metabolism Tests
*Cholesterol
* Present in all tissues
* Serves as the skeleton for many hormones
* Recommended to be less than 200 mg/dL in adults)
* LDL = “bad” cholesterol; HDL = “good” cholesterol
*Triglycerides
* Main storage form of lipids, comprising 95% of fat tissue
* Hyperlipidemia – having high blood levels of triglycerides – may increase risk of heart attack
*Carbohydrate Metabolism Tests
*Glucose - Largely regulated by insulin
*Thyroid Function Tests
*Thyroid Stimulating Hormone (TSH) - Inverse relationship to thyroid function (the higher the TSH, the lower the thyroid function and vice versa)
*Other less common thyroid tests include T3 and T4
*Hypothyroidism – underactive thyroid gland
*Hyperthyroidism – overactive thyroid gland
Basic Clinical Chemistry.ppt
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