Introduction to Laboratory_lect 02-08

8/13/2019 Introduction to Laboratory_lect 02-08

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INTRODUCTION TO LABORATORY

MEDICINE (CLINICAL LABORATORY)

DR. dr. Tinny Rasjad SpPK (K)


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CLINICAL LABORATORY

CLINICAL PATHOLOGY

MICROBIOLOGY

PARASITOLOGY


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LEARNING OBJECTIVE

1. Understand the use of laboratory tests in clinical practice.

2. Define the sensitivity, specificity, reliability, and accuracy of a laboratory

test.

3. Define the predictive value of positive and negative test results and how

they vary with changes in the prevalence of disease.

4. Understand the meaning of the reference interval of a test and how it is

manipulated to increase the test's sensitivity and specificity.

5. Understand the principles of anticoagulation in blood collection tubes and

the differences between plasma and serum.

6. Define and give examples of pre-analytical, analytical, and post-analytical

variables that affect laboratory tests.

7. Understand patient factors that alter tests results such as age, sex, habits and

underlying disease.


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General Laboratory (General Principles

of CLINICAL LABORATORY)

CLINICAL CHEMISTRY

HEMATOLOGY

HEMOSTASIS AND THROMBOSIS

BLOOD BANK URINALYSIS AND OTHER BODY FLUIDS

IMMUNOPATHOLOGY

MEDICAL MICROBIOLOGY

MEDICAL PARASITOLOGY MOLECULAR PATHOLOGY


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Schedule:

First half semester (7 weeks)

Lab. Clinical pathology + Middle test

6 weeks lecture + seminar

Introduction

Hematology

Urinalysis

Clinical chemistry

Serology


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Second half semester (7 weeks):

Microbiology & Parasitology + middle test + final test

Six weeks (lecture)

4 weeks: Microbiology: Staining (Gram; BTA, etc) 2 weeks: Parasitology: Malaria, Toxoplasmosis, etc


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Grouping

A (80 students) Amphy room

B (80 students) Class room II ( 3rdfloor of

Physiology Laboratory Building)

EC (English class) English class room (4thfloor ofnew building)


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Clinical Pathology Seminar

A / B groups:

Divided into 4 groups (20 students each)(KBK room no. 3.17 to 3.20)

Each group to be divided into 3 sub groups (6-7 students

each)

English class:

Divided into 2 groups (20-30 students each)

(KBK room no. 3.15 & 3.16)

Task Group:Submitted 3 days before seminar


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The use of laboratory tests in clinical

practice.

Interpretationof results

Determinationof additionalclinical

informationneeds

Selection oflaboratory

studies

Laboratorystudy results

Interpretationof results

Clinicalobservation

Selection oflaboratory

studies

Cyclic structure of the use of medical studies

Clinical

assessment


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The role of the laboratory test

1. Screening Detect subclinical disease

Detect and quantify the risk of future disease

2. diagnoses

Establish and exclude the presence of disease in symptomat

persons ( in differential diagnosis )3. Helpful patient management

Assess disease severity

estimate prognoses

Detect disease recurrent

Select appropriate therapy

Monitor disease progress and treatment effect


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Clinical information need for lab. test

1. Assess organ functional status

2. Assess metabolic activity

3. Assess macro- and micronutritional status

4. Detect and quantity tissue injury

5. Detect and monitor neoplastic condition

6. Detect and identify infectious agent

7. Detect and identify intoxicants and poisons8. Monitor therapeutic agents


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ALSO PLAY A LEADING ROLE IN

EDUCATION AND RESEARCH

INFORMATION TECHNOLOGY DESIGN AND

IMPLEMENTATIONQUALITY IMPROVEMENT


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Perfect Test

1). Accurate

2). Precise

3). Discriminating

4). Pain free

5). Risk free

6). Inexpensive

7). Useful


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Role of lab tests

Correct diagnosis

Appropriate therapy

Restoration of patient health to normal


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Diagnosis

Diagnosis is most important; a test or procedure that helps

detect, confirm, document or exclude a disease. Once a disease

is suspected, further tests aimed to increase or decrease the

diagnostic certainty of one diagnosis to the exclusion of others.


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Prognosis

Prognosis can be predicted, for example, by noting the degree

of test abnormality. The higher the transaminase level in

hepati tis, and the higher the creatine kinase MB isomer level in

acute myocardial infarction, the more ser ious the disease andusually the worse the prognosis.


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Symptomatic Patients:

1. Non-specific complaints

2. Specific problem already identified


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Non-specific Complaints

1. Battery of chemistry tests

2. CBC (Cellular Blood Count)

3. Urinalysis

Problem: Positive test false positive results

Solution: Repeat abnormal test


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Specific problem

Defined set of differential diagnosis

Screening tests to pare down differential diagnosis (high sensitivity for a

disease)

1). test negative disease excluded

2). test positive true positive

false posiitive USE TEST(S) WITH HIGH SPECIFICITY


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Test characteristics

Normal: A term with many meanings, including those persons in thenondiseased population and an equivalent term for a gaussian

distribution

Abnormal: test result outside of reference intervals observed in people

with desease or in less than good health

Reference interval : the interval between including two reference limit

Cut off value : limit above or below which the patient is abnormal or

positive for a condition such as substance abuse

Prevalence: the number of persons who have a disease in a given

population at any one point in time, or more often the rate of such

disease, which is also called the disease frequency


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Specificity: the probability that a laboratory test will

be negative in the absence disease; defined as a true

negatives divided by the sum of true negatives and

false positive

Sensitivity: probability that a laboratory test is

positive in the presence of disease; defined as true

negatives divides by the sum of true positives and false

negative


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Predictive value : probability that a laboratory result accurately

reflects the true presence or absence of disease

Positive predictive value : probability that a lab. result outside

the reference interval actually reflects the presence of disease;

defined as true positive divides by the sum of true positives and

false positives Negative predictive value : probability that a lab. result falling;

defined as true negatives divided by the sum of true negatives

and false negatives


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Predictive value

Condition(e.g. Disease)

As determined by "Gold"

standard

True False

Test

outcome

Positive True Positive False Positive Positive

Predictive Value

Negative False Negative True Negative Negative

Predictive Value

Sensitivity

SpecificityAccuracy
http://en.wikipedia.org/wiki/Sensitivity_(tests)http://en.wikipedia.org/wiki/Specificity_(tests)http://en.wikipedia.org/wiki/Specificity_(tests)http://en.wikipedia.org/wiki/Sensitivity_(tests)


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Precision

Test precision is a measure of a test

reproducibility when repeated on the same

sample.

Reproducibility within day and between day

An imprecise test is one that yields widely

varying result on repeated measurement High precision but low acc

A
http://upload.wikimedia.org/wikipedia/commons/3/3a/High_precision_Low_accuracy.svg


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Accuracy

The accuracy of laboratory test is its

correspondence with true value

The accuracy test is maximized by

calibrating laboratory equipment withreference material and by participation in

external quality control program High accuracy but low precis
http://upload.wikimedia.org/wikipedia/commons/1/10/High_accuracy_Low_precision.svg


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High precision and accuracy


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Normal Range & Interpretation of

Results

The "normal range" of the mean plus or minus 2 S.D.

is a purely statistical concept - by definition 2.5% of

healthy individuals will have values exceeding this. In

addition, in statistical terms "normal" implies a

Gaussian distribution

ex. Normal plasma sodium 136148 mmol/L


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( i )


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NORMAL RANGE

3.3-5.2 mg/dl

DEFINITION

This is the major protein in the blood, made only by the

liver. It makes up the largest part of the Total Proteinlevel. It maintains the fluid balance in your body.

EXPLANATION OF TEST RESULT

A low level liver disease

Alb (Albumin)


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Normal Range

Reference values: urea - 10-20 mg/dl

200 mg/dl?

40 mg/dl?

25 mg/dl? could be a false positive?

* How much above normal must the test result be before

an intensive chain of studies is set into motion to

determine the cause of the alleged abnormality?


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FACTORS AFFECTING LAB.

VARIATION

PRE-ANALYTICAL

ANALYTICAL

POST-ANALYTICAL


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PRE-ANALYTICAL VARIATION

Precollection causes of variation

Cyclic biological variables

Patient-related physical variables

Normal variation in reference interval Blood collection causes of variation

Blood collection technique

Types of blood sampleError related to preservatives and anticoagulants


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Postcollection causes of variation

Sample transportation

Sample processing

Sample storage Other preanalytical collection concerns

Urine collection : sources of variation

Specimen collection from infants

Computer-based aids for error detection

Criteria for rejection of spesimens


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Normal variations in reference intervals

a. Newborns

b. Children

c. Adult men

d. Adult women

e. Pregnant women

f. Geriatric population


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Collection of Blood

Plasma anticoagulant in the collection

tube

chelating agents(EDTA,citrate)

orheparin(enhance antithrombin3)

Centrifugation - 3 layers

a. plasma

b. buffy coat(WBC,platelets)c. RBCs

S ti l t


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Serum no anticoagulant

blood clots centrifugation

deficient in fibrinogen

prothrombin

factor V

factor VIII

platelets

I t t l V i ti (A l ti )


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Instrumental Variation (Analytic)

Method and technique variationAnalytic bias andvariability

To overcome:

Intra & inter- laboratory quality control (precision,

accuracy, coefficient variation)


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QUALITY CONTROL

QUALITY CONTROL:

Assessment & Control of ANALYTICALVariability

Used in daily operations of clinical lab. assessprecision over time within a single clin. Lab

Quality Control : internal and external QC


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INTERNAL QUALITY CONTROL

Used daily operations

Primary asses precision and method during the day

Type :

within run , with replicated result of singleperformance group together

between run, with replicated result from number of

different runs group together


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External quality control

External QC procedure To assess accuracy of lamethod across of numb

laboratory

P l i l V i i


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Post-analytical Variation

Result of the measurement

Report the measurement sent to the requesting

physician.

Interpretation laboratory resultSensitivity & Specificity in diagnosis testing

Predictive value

Post-collection Causes of Variation


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Post-collection Causes of Variation

Result of the measurement

Interpretation resulting

Specificity,sensitivity,p

redictive value


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Introduction to Laboratory_lect 02-08

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