Interpretation of laboratory Tests

General & Cardiovascular System

Hadeel Alkofide MScPHCL 326May 2011

Learning Objectives Differentiate between invasive & noninvasive tests

State the clinical application of common general diagnostic procedures

Identify the clinical application of specific laboratory tests

Identify the clinical application of specific diagnostic procedures

Assess common laboratory & diagnostic test results

Introduction

Introduction Data from laboratory & diagnostic tests & procedures

provide important information regarding

The response to drug therapy

The ability of patients to metabolize & eliminate specific therapeutic agents

The diagnosis of disease, & the progression & regression of disease

IntroductionInvasive tests

Require penetration of the skin or insertion of instruments or devices into a body orifice

The degree of risk varies from relatively minor risks such as pain, bleeding, & bruising associated with venipuncture to the risk of death associated with more invasive procedures such as coronary angiography

E.g venipuncture, insertion of a central venous catheter, & collection of cerebrospinal fluid

IntroductionNoninvasive tests

Do not penetrate the skin or involve insertion of instruments into body orifices & pose little risk to the patient

E.g. include chest radiograph, analysis of spontaneously voided urine, & stool occult blood analysis

Introduction The selection of specific tests & procedures depends on

The patient's underlying condition The need for the information The degree of risk

Reference ranges are listed in Tables 5-1 through 5-7 Results are interpreted using laboratory specific reference

ranges Reference ranges may differ among different laboratories

depending on the population & laboratory methodology used to establish the range

IntroductionFactors to consider when interpreting individual test

resultsPatient ageGender Timing of the test result in relationship to drug administration Concomitant drug therapyConcurrent diseases, organ function (renal, liver, cardiac)Test sensitivity (the proportion of true-positive results)Test specificity (the proportion of true-negative results)Timing of the test in relation to drug dosing or known circadian rhythmsGenetics (e.g., glucose-6-phosphate deficiency)Fluid status (e.g., euvolemia, dehydration, fluid overload)

General Organ System Monitoring

General Organ System Monitoring

A variety of tests & procedures are used to diagnose & monitor conditions that affect various organ systems

The applications & uses of these tests & procedures continue to expand with experience & the integration of new technology

General Organ System Monitoring

Angiography

A radiographic test used to evaluate blood vessels & the circulation

Radiopaque material is injected through a catheter & images are recorded using standard radiographic techniques

Biopsy

Removal & evaluation of tissue

General Organ System Monitoring

Angiography

General Organ System Monitoring

Computed Tomography

(CT; CAT scan) uses a computerized X-ray system to produce detailed sectional images

The system is very sensitive to differences in tissue density & produces detailed, two-dimensional planar images

Contrast agents increase attenuation

The spiral or helical CT takes pictures continuously, decreasing the time needed to obtain images

Computed Tomography

General Organ System Monitoring

General Organ System Monitoring

Doppler Echography

Uses ultrasound technology to measure shifts in frequency from moving images

E.g, Doppler echography is used to evaluate blood flow velocity & turbulence in the heart (Doppler echocardiography) & peripheral circulation

General Organ System Monitoring

Doppler Echography

General Organ System Monitoring

Endoscopy

Used to examine the interior of a hollow viscus (e.g., digestive, respiratory, & urogenital organs & the endocrine system) or canal (e.g., bile ducts, pancreas)

The endoscope, a flexible or inflexible tube with a camera & a light source, is inserted into a body orifice (Figure5-1)

Still &/or video images are recorded & tissues obtained for biopsy or other laboratory diagnostic tests

General Organ System Monitoring

Endoscopy: Examples of common endoscopic procedures

Colonoscopy: views the inside of the entire colon from rectum to end of the small intestine

Sigmoidoscopy: views the inside of the large intestine from the rectum through the sigmoid colon

Cholangiopancreatography: views the inside of the bile ducts & pancreas

Esophagogastroduodenoscopy: views the inside of the esophagus, stomach, & duodenum

Bronchoscopy: views the inside of the tracheobronchial tree

General Organ System Monitoring

Fluoroscopy

Uses a fluoroscope, a device that makes the shadows of x-ray films visible, to provide real-time visualization of procedures

It exposes a patient to more radiation than routine radiography but often is used to guide needle biopsy procedures & nasogastric tube advancement

General Organ System Monitoring

Magnetic Resonance Imaging Uses an externally applied magnetic field to align the axis

of nuclear spin of cellular nuclei The patient is surrounded by the magnetic field (Fig. 5-2) Brief radio frequency pulses are applied to displace the

alignment The energy emitted when the displacement ends is

detected resulting in finely detailed planar & three-dimensional images

Contrast agents increase the attenuation

General Organ System Monitoring

Magnetic Resonance Imaging

General Organ System Monitoring

Paracentesis

The removal & analysis of fluid from a body cavity

Plethysmography

Measures changes in the size of vessels & hollow organs by measuring displacement of air or fluid from a containment system

Body plethysmography is used to assess pulmonary function

General Organ System Monitoring

Plethysmography

General Organ System Monitoring

Positron Emission Tomography (PET)

Uses positron-emitting radionuelides to visualize organs & tissues of the body

The radionuclides decay, producing positrons that collide with electrons

A special camera detects photons, released when the positrons & electrons collide

It provides quantitative information regarding the structure & function of organs & tissues

General Organ System Monitoring

Positron Emission Tomography (PET)

General Organ System Monitoring

Single-Photon Emission Computed Tomography. (SPECT) Similar to PET but involves the administration of

radionuclides that emit gamma rays

It is less expensive than PET but provides limited image resolution

General Organ System Monitoring

Standard Radiography (Plain Films, X-Ray Films)

Produces images on photographic plates (Figure 5-3)

These films are sometimes difficult to interpret because the three dimensionality is lost on the planar images

General Organ System Monitoring

Ultrasonography (Echography)

Uses ultrasound (high-frequency waves imperceptible to the human ear) to create images of organs & vessels

Ultrasonography is used to visualize the fetus in uterus

Cardiovascular

Laboratory Tests Cardiac Enzymes

• The pattern & time course of the appearance of enzymes in the blood after cardiac muscle cell damage are used to diagnose MI

Creatine Kinase

Lactic dehydrogenase (LDH)

Troponins

Cardiovascular

Laboratory TestsCardiac Enzymes Creatine Kinase

Found in skeletal & cardiac muscle, brain, bladder, stomach, & colon

Isoenzyme fractions identify the type of tissue damaged

CK-MB(CK2) is found in cardiac tissue

CK-MB is detected in the blood within 3 to 5 hours after a MI

Levels peak in about 10 to 20 hrs & normalize within about 3 days

Cardiovascular

Laboratory TestsCardiac Enzymes Lactic dehydrogenase (LDH)

Found in a variety body tissues

Isoenzyme fractions used to identify type of tissue damage

LDH1- LDH2 are found in the heart, brain, & erythrocytes

LDH 2 accounts for the highest % of total serum LDH

After a MI the rise in LDH 1 > the rise in LDH2

LDH ↑ within 12 hrs after an MI

It Peaks 24 to 48 hrs, & normalizes by about-day 10

Cardiovascular

Laboratory TestsCardiac Enzymes Troponins

A complex of proteins (Troponin I, C, & T) that mediate the actin & myosin interaction in muscle

Troponins I & T are specific to cardiac muscle & are used to identify cardiac muscle injury

Their concentrations ↑ within a few hrs of cardiac muscle injury & remain elevated for 5-7 days

Cardiovascular

Laboratory Tests Cardiac enzymes:

CK-MB = Creatinine Kinase-MyoGlobin

Cardiovascular

Laboratory Tests Cholesterol

Low-density lipoprotein (LDL)is strongly correlated with coronary artery disease

High density lipoprotein (HDL)is inversely correlated with coronary artery disease

Triglycerides Found in very low density lipoproteins (VLDLs) &

chylomicrons

Cardiovascular

Laboratory Tests C-Reactive Protein

It is a biologic marker of systemic inflammation.

Preliminary studies have linked an ↑ C-reactive protein with an ↑ risk of MI, stroke, & peripheral arterial disease

Myoglobin. A small protein found in cardiac & skeletal muscle

The presence of myoglobin in the urine or plasma is a relatively sensitive indicator of cellular damage

Cardiovascular

Diagnostic Tests & Procedures Cardiac Catheterization

Used to evaluate cardiac function

A catheter is passed into the right or left side of the heart

Right-sided catheterization is used to measure right atrial pressures, right ventricular pressures, pulmonary artery pressures, & pulmonary artery occlusion pressure

Left-sided catheterization is used to measure left ventricular pressures

Cardiovascular

Diagnostic Tests & Procedures Chest Radiography.

Chest x-ray films are used to diagnose cardiac disease & monitor the patient's response to drug & nondrug therapy

The chest radiograph is used to determine the size & shape of the atria & ventricles, to calculate the cardiothoracic ratio, & to detect abnormalities in the lung fields & pleural spaces

Coronary Angiography In coronary angiography the cardiac vessels are visualized

by injecting the vessel with a contrast agent

Cardiovascular

Diagnostic Tests & Procedures Echocardiography

Used to evaluate the size, shape, & motion of the valves, & walls & changes in chamber size during the cardiac cycle

Cardiovascular

Diagnostic Tests & Procedures Electrocardiogram (ECG)

Records the electrical activity of the heart (Figure 5-5)

used to diagnose cardiac disease, monitor the patient's response to drug therapy, & monitor for adverse drug effects

12 separate leads, 6 extremity (limb) leads & 6 chest leads create a three-dimensional view of cardiac electrical activity

Cardiovascular

Diagnostic Tests & Procedures Electrocardiogram with Stress (Stress Test)

The ECG is recorded during standardized exercise protocol with gradually increasing level of exercise or with patient at rest after administration of dobutamine or dipyridamole

Either intervention increases myocardial oxygen consumption and blood flow

BP, HR, O2 consumption, O2 saturation, & arterial blood gases are collected to provide a thorough assessment of how the CV system functions under stress conditions

Cardiovascular

Diagnostic Tests & Procedures Electrocardiography

Holter Monitoring (Ambulatory Electrocardiography) A portable recorder to record the ECG continuously

throughout usual patient activity Thallium Stress Test

It combines the parenteral administration of thallium-201, a radionuclide taken up by healthy myocardial tissue, and the stress test (either exercise or pharmacologic)

A gamma camera is used to record serial images of the myocardium

Cardiovascular

Diagnostic Tests & Procedures Technetium-99m Pyrophosphate Uptake.

Infarcted myocardial tissue has an increased uptake of technetium-99m compared with healthy tissue

The isotope is injected parenterally, & serial images of the heart are obtained to evaluate the location & extent of the myocardial infarction

Cardiovascular

Thank You