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Chapter 16 Interpreting Clinical and Laboratory Data

Chapter 16 Interpreting Clinical and Laboratory Data. Learning Objectives. Describe what a critical value is and state its importance in clinical practice. Define the following terms related to clinical lab tests: leukocytosis, leukopenia, anemia, polycythemia, and thrombocytopenia.

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Chapter 16 Interpreting Clinical and Laboratory Data

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  1. Chapter 16Interpreting Clinical and Laboratory Data

  2. Learning Objectives Describe what a critical value is and state its importance in clinical practice. Define the following terms related to clinical lab tests: leukocytosis, leukopenia, anemia, polycythemia, and thrombocytopenia. Identify which electrolyte disturbances interfere with normal respiratory function.

  3. Learning Objectives (cont.) • Describe clinical tests used to identify cardiac stress and myocardial infarction. • Identify the three main tests used to diagnose coagulation disorders. • Describe how the sputum Gram stain and culture are used to diagnose patients with pulmonary infections.

  4. Clinical Laboratory Tests • Evaluates Patients: • Health status • Identify organ-system dysfunction • Detect presence of infection • Effects of therapy

  5. Intro to Laboratory Medicine • Divided into 5 major disciplines • Clinical Biochemistry – analysis of blood, urine & bodily fluids • Hematology – analyzes cellular components of blood • Microbiology – analysis of blood & other bodily fluids for presence of infectious agents • Immunology – focuses on autoimmune & immune deficiency diseases • Anatomic Pathology – analysis of tissue for diagnosing disease

  6. Reference Range • Also referred to as Biological Reference Intervals or Expected Values • Takes into account variations related to: • Age • Gender • Race • Ethnicity • Vary slightly from laboratory to laboratory

  7. Critical Test Value • Result significantly outside reference range • Represents pathophysiologic condition • May represent potentially life threatening situation

  8. The normal or expected boundaries for any analysis such as electrolytes, blood cells, proteins, or enzymes that would likely be encountered in healthy subjects is called a: Reference range Critical value Range level Normal value

  9. Complete Blood Count (CBC) Common test measuring formed elements of blood Counts & examines: Leukocytes (white blood cells) Erythrocytes (red blood cells) Thrombocytes (platelets)

  10. Complete Blood Count (CBC) (cont.)

  11. ___________are evaluated for size and hemoglobin content. • White blood cells • Red blood cells • Platelets • Proteins

  12. Complete Blood Count (cont.) White Blood Cell Count WBC count above normal is called leukocytosis Leukocytosis - common with infection, stress, & trauma. Degree of leukocytosis depends on severity of infection Severe infection with mild leukocytosis may represent poor prognosis

  13. Complete Blood Cell Count (cont.) White Blood Cell Count Below normal represents leukopenia (leukocytopenia) Occurs with overwhelming infections & when immune system is depressed due to disease or certain cancer therapies (chemotherapy) Diseases of bone marrow (e.g., leukemia) can cause leukopenia

  14. Differential of WBC Count White blood cells come in 5 varieties Neutrophils (40-75%) Eosinophils (0-6%) Basophils (0-1%) Monocytes (2-10%) Lymphocytes (20-45%) Leukocytosis is most often due to elevation of only 1 of 5 types of white blood cells

  15. Differential of WBC Count (cont.) • Neutrophilia: Elevation of absolute value of neutrophils • Bands: Immature neutrophils • Segmented neutrophils (segs): mature neutrophils • When bands & segs are elevated in CBC, patient is likely experiencing more severe bacterial infection

  16. A significant elevation of the WBC count (more than 15 x 103/mcL) will occur only when either neutrophils or __________ are responding to an abnormality. • Basophils • Eosinophils • Monocytes • Lymphocytes

  17. Red Blood Cell Count Reduced RBC count is called anemia Anemia is due to either blood loss or reduced RBC production by bone marrow Anemia reduces oxygen-carrying capacity of blood Several types of anemia exist with different causes (dietary deficiencies, chronic inflammatory disease, hereditary) Severe anemia is treated with transfusion

  18. Red Blood Cell Count (cont.) Abnormal elevation of RBC count is known as polycythemia Secondary polycythemia occurs when bone marrow is stimulated to produce more RBCs in response to chronically low blood oxygen levels Common in people who live at an elevated altitude & in patients with chronic hypoxemic lung disease

  19. Red Blood Cell Count (cont.) Includes hemoglobin & hematocrit levels Hemoglobin (Hb) Plays role of bonding with oxygen Normal hemoglobin concentration is 12-17 g/dL RBCs with reduced hemoglobin are smaller than normal (microcytic anemia) & lack normal color (hypochromic anemia). An RBC transfusion depends on cause of anemia & patient’s overall condition

  20. Red Blood Cell Count (cont.) • Hematocrit Levels • Ratio of RBC volume to that of whole blood • Proportion of sample represented by packed cells • Low levels occur with anemia or over-hydration • High levels occur with polycythemia & dehydration

  21. A patient’s results on a blood test shows that her hematocrit percentage is approximately 20%. What should the clinician recommend for this patient? • nothing, patient’s result is normal • patient should receive a blood transfusion • repeat test due to erroneous result. • patient should undergo plasmaphoresis

  22. Electrolyte Test • Basic Concepts • Normal cellular function depends upon homeostasis of fluid, electrolytes & acid-base balance • Electrolytes are charged ions influencing functioning of enzymes • Enzymes are proteins regulating all chemical reactions occurring within cells (metabolism, protein synthesis)

  23. Electrolyte Tests (cont.) • Basic Concepts (cont.) • 1 points when interpreting blood test • Series of blood samples provides insight of severity & progression of disease & effectiveness of therapy • Intravascular blood compartment (extracellular environment) is separate from intracellular environment. Thus, blood samples provide important, but indirect information of intracellular electrolytes

  24. The ability of a complex organisms to maintain a dynamic balance or equilibrium in their internal environment by making constant adjustments is called • homeostasis • electrolytes • cellular function • polycythemia

  25. Electrolyte Tests (cont.) Basic Chemistry Panel Predominant electrolytes measured in lab: Sodium (Na+) Potassium (K+) Chloride (Cl-) Total CO2 / bicarbonate (bicarb) Glucose (GL) Excretion of renal-mediated waste products is included in panel : Creatine (Cr) & blood urea nitrogen (BUN). More comprehensive metabolic panel would include: Magnesium, Phosphorus, Calcium

  26. Electrolyte Tests (cont.) • Glucose • Formed from breakdown of carbohydrates • Metabolized by cells for energy • Requires insulin to be utilized by cells • Hyperglycemia • Elevation of blood glucose • Often result of diabetes

  27. Electrolyte Tests (cont.) • Glucose (cont.) • Hypoglycemia • Reduced glucose level • May result from inadequate diet or drug induced • Diabetes • Diagnosed by fasting blood glucose levels • Indicated by 140 mg/dL on two occasions • Severe hyperglycemia occurring with metabolic acidosis is consistent with diabetic ketoacidosis

  28. A medical resident asks for your advice in assessing renal function in a critically ill patient. You would suggest to test for all of the following: 1. glucose (GL) 2. BUN 3. Creatinine 4. Sodium (Na+) • 1, 2 and 3only • 2 and 3 only • 1 and 4only • 1, 2, 3 and 4

  29. Electrolyte Tests (cont.) • Anion Gap • Metabolic acidosis is caused by addition of non-volatile acids or loss of HCO3- • Determines if decrease in HCO3- is caused by disruption of normal anion balance or presence of abnormal acid anion • Normal level is 8-14 mmol/L

  30. Electrolyte Tests (cont.) • Lactate • End product of anaerobic glucose metabolism • Overproduction or insufficient metabolism results in lactate acidosis • Abnormal levels can be found in anaerobic metabolism, diabetes mellitus & malignancies • Initial values of serum lactate > 4 mmol/L are associated with higher mortality in patients with septic shock

  31. Enzyme Tests • Liver Function Test • Liver damage is assessed by abnormal increases in hepatic enzymes • Total bilirubin (TBIL) – crucial component of liver panel • Total protein (TP) & albumin (ALB) used to asses protein synthesis

  32. Enzyme Tests (cont.) • Pancreatic & Muscle Enzyme Tests • Pancreatitis will have abnormal levels of pancreatic enzymes lipase & amylase • Suffering ischemic damage to the heart, brain, & skeletal muscle tissue will have elevated creatine phosphokinase (CPK) • Increased levels of lactate dehydrogenase (LD) is associated with tissue breakdown

  33. Enzyme Tests (cont.) • Cardiac Enzyme & Protein Tests • Most common CPK enzyme test is for CPK-2 which is released from heart following MI • Troponin-I (protein fragment) levels peak 12-16 hours after MI • B-Type Natriuretic Peptide (BNP) is used to evaluate patients for heart failure

  34. A 67-year old female is assessed with abnormal increases in the enzymes alanine aminotransferase (ALT), aspartate aminotransferase (AST), as well as alkaline phosphatase (ALK). What does this indicate? • respiratory problem. • kidney damage. • pancreas disorder. • liver damage.

  35. Enzyme Tests (cont.) • Coagulation Studies • Thrombocytopenia (low platelets) & thrombasthenia (abnormal platelet functioning) leads to excessive bleeding • Thrombocytosis (excessive platelets) causes excessive clotting

  36. Enzyme Tests (cont.) • Coagulation Studies • Measured by • Prothrombin Time (PT) • Partial Thromboplastin Time (PTT) • PT is accompanied by an additional measurement - International Standardized Ratio (INR)

  37. Enzyme Tests (cont.) • Coagulation Studies • D-Dimer • Found in blood when fibrin clots are dissolving • Help diagnose the presence of deep vein thrombosis, pulmonary embolism or disseminated intravascular coagulation (DIC) • Protein C • Regulates coagulation • Active state (Activated Protein C (APC)) inhibits coagulation & promotes degradation of clots

  38. Enzyme Tests (cont.) • Sweat Chloride • Cystic Fibrosis (CF) • CF patient’s have elevated level of sweat Cl- • 40-60 mmol/L is borderline • <40 mmol/L are unlikely to be diagnosed • Must be accompanied by other tests to confirm diagnosis

  39. Microbiology • Sputum Gram Stain • Suspected infection in lungs or airways may benefit from analysis of sputum sample • Legitimate sputum sample will have numerous pus cells & few epithelial cells • Gram stain can determine if offending organism is gram positive or gram negative & its shape • Culture can identify specific organism • Determine organisms sensitivity to antibiotic therapy

  40. Microbiology (cont.) • Acid-Fast Testing • Identifies acid-fast bacterium • Steps: • Gram stain sputum sample • Acid wash sputum sample • If organism is resistant to decolorization, then it is classified as an acid-fast bacterium

  41. Coagulation Disorders • Must check patient’s clotting levels prior to performing an arterial blood gas (ABG) or nasotracheal suctioning • Abnormally low platelet count or an elevated PT and INR will need an ABG puncture site compressed for longer time to prevent bleeding & hematoma • Extremely low platelet count should have an ABG or nasotracheal suctioning done only when necessary

  42. Electrolyte Disorders • Severe levels have profound impact on pulmonary function • Causes skeletal muscle weakness that may limit ambulation - may lead to development of pneumonia • Causes respiratory muscle weakness impairing ability to sustain spontaneous ventilation & maintain pulmonary hygiene

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