Chapter 16 interpreting clinical and laboratory data
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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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Chapter 16Interpreting 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.

Identify which electrolyte disturbances interfere with normal respiratory function.


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.


Clinical Laboratory Tests

  • Evaluates Patients:

    • Health status

    • Identify organ-system dysfunction

    • Detect presence of infection

    • Effects of therapy


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


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


Critical Test Value

  • Result significantly outside reference range

  • Represents pathophysiologic condition

  • May represent potentially life threatening situation


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


Complete Blood Count (CBC)

Common test measuring formed elements of blood

Counts & examines:

Leukocytes (white blood cells)

Erythrocytes (red blood cells)

Thrombocytes (platelets)


Complete Blood Count (CBC) (cont.)


  • ___________are evaluated for size and hemoglobin content.

  • White blood cells

  • Red blood cells

  • Platelets

  • Proteins


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


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


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


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


  • 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


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


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


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


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


  • 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


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)


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


  • 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


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


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


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


  • 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


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


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


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


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


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


  • 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.


Enzyme Tests (cont.)

  • Coagulation Studies

    • Thrombocytopenia (low platelets) & thrombasthenia (abnormal platelet functioning) leads to excessive bleeding

    • Thrombocytosis (excessive platelets) causes excessive clotting


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)


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


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


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


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


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


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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