24 - Fundamentals of Clinical Lab

Question 1

Difference between

Invasive vs Non-invasive

Tests

Answer 1

Invasive tests** use a **DEVICE
needle / tubes -> to enter body to collect samples

Noninvasive tests use samples obtained WITHOUT DEVICE
exhaled air / sputum/ urine

Question 2

Difference between

Analyte vs Biomarker

Answer 2

Analyte = substance measured by an assay/test
ex. proteins / drugs / vitamins / hormones
typically contained in a specimen / sample

Biomarker** = **characteristic that is objectively measured/evaluated
as an INDICATOR OF A BIOLOGICAL PROCESS
drug response / pathology

Question 3

Aside from Blood / Urine what are some

Less-Common Samples?

Answer 3

• *Feces**
• *Occult Blood** test

Sweat
analysis of increased electrolytes for CYSTIC FIBROSIS

Saliva
analysis of drugs / virus / bacteria

Synovial / Cerebrospinal / Amnionic

Question 4

Common ANALYTES examined in physiological samples

Answer 4

Proteins / AA’s / Nitrogen metabolites

Electrolytes / trace elements

Lipids / Enzymes / Hormones

Drugs / Vitamins / small organics

Question 5

What are some of the Most Common Errors

in Sample Analysis

and how can we avoid them?

Answer 5

MIS-IDENTIFICATION of the patient
check/confirm patients name & ID etc

Add more information

• *MIS-LABELED samples**
• usually only found when test results are UNEXPECTED*

Question 6

Pharmacist role in Clinical Labs

Answer 6

Interpreting Lab Results
basic grasp of lab terminology / technology / statistics of testing

Pharmacists may be involved in:

Sample Collection / Handling

Reporting / Disposal

Question 7

PRE-Collection Causes of VARIABILITY

in sample colection

Answer 7

Circadian Rhythms
the 24 hour cycle of concentration of various biochemicals in the body:
Melatonin = excreted in darkness
Iron / Acid Phosphatase / Electrolytes / Bone-turnover markers

• *Diurnal Changes**
• *TIMING** - Sleep / Wake cycle needs to be considered

Question 8

Affect of Supine -> Standing on sample collection

Physiological Variable - Posture

Answer 8

• *Supine -> Standing**
• Reduce pt’s blood volume by 10%,*

which in turn INCREASES:
apparent concentration of drugs / enzymes / calcium

Question 9

Affect of UPRIGHT POSTURE on sample collection

Physiological Variable

Answer 9

Upright:

Induces LOW SECRETION of Various Hormones:

Catecholamines / Aldosterone / Renin / Others

Question 10

Affect of Prolonged Bed Rest on sample collection

Physiological Variable

Answer 10

Fluid RETENTION

Lower concentrations of PROTEINS

induces elevated NITROGEN EXCRETION

Question 11

Affect of Brief / Mild Exercise on sample collection

Physiological Variable

Answer 11

strenuous exercise -> exaggerated effects of mild exercise

RAISE:

Blood Glucose / Lactate / Several Enzymes

Decrease:

serum TG’s / Cholesterol
can persist for days

Question 12

Affect of FOOD INGESTION on serum collection

Physiological Variables

Answer 12

RAISES levels of many analytes:

Glucose / TG’s

Iron / Sodium / Lactate Dehydrogenase

Question 13

Blood Collection Technique

Blood has: Plasma / RBC / WBC / Platelets

serum = liquid that seperates when blood clots

Answer 13

Venipuncture = Phlebotomy, injection into the blood vessel

done AFTER 20 MIN REST, avoid HEMODILATION effects

Clean/Dry site, no alcohol remaining

collected in:

• *VACUTAINERS** = Evacuated tubes, closed by rubber septum
• different interior coats to promote/retard clotting*

Question 14

Difference between

HEPARIN Plasma & SERUM

Answer 14

Heperinized plasma = Serum with fibrinogen (it clotted)

Serum then has lower TOTAL protein

Serum is HIGHER in potassium from platelets
platelets –> release potassium during clotting

Question 15

Heparin Related ERRORS

Answer 15

heparin can displace Thyroxine from serum proteins

• -> Falsely HIGH reading
• *thyroid issue**

Heparin salts contain ammonium or lithium
–> falsely HIGH readings of these cations

Question 16

EDTA related ERRORS

EDTA chelates divalent metal ions = Ca / Fe
inactivates certain enzyes

Answer 16

• *Collect EDTA-blocked samples LAST!!!**
• to avoid cross-contamination*

EDTA will PROLONG CLOTTING TIMES
due to calcium chelation

• may lower / falsely low readings of:*
• *iron / calcium / magnesium**

Question 17

Blood sample POST-Collection Errors

Answer 17

Delays of <1 hour are generally well tolerated

Avoid THAWING of frozen samples

For Remote sites: best to
Seperate Plasma/serum physically from cells BEFORE transport

Question 18

Vacutainer

Answer 18

Evacuated tubes, closed by a rubber septum
used for BLOOD SAMPLES

Different sizes / interior coatings that
PROMOTE/RETARD CLOTTING

often have a preferred order in which they are drawed

Question 19

What are the 3 Types of URINE SAMPLES?

Answer 19

Random Sample
Timing is not critical, used typically for drugs of abuse

FIRST MORNING = 8-hour sample
most Concentrated, preferred for microscopic exam
testing for proteins / homones, that may have intrinsicly low conc.

Timed Specimen
patient may need cautions on diet restrictions / drug ingestion
1 / 4 / 24 hour etc

Question 20

What is a Clean-Catch Specimen?

Urine Samples

Answer 20

• *MID-STREAM** Sample
• however first 10mL is useful for bacterial examination*

no contact w/ bacteria or foreign substation
or perineum

Sterile Container

Double-Voided Sample
timed sample following complete bladder emptying:
done esp for glucost tolerance test (GTT)

Question 21

Accuracy is a measure of ?

Answer 21

NON-Random / Systematic Error or Bias

How FAR your measurement is
from the TRUE value

Question 22

Precision is the descriptor of?

Answer 22

RANDOM VARIATION in a population of data

Ability to produce the same value in REPLICATE testing

Question 23

Diagnostic SENSITIVITY

and its Math value

Answer 23

“senSITIVE = poSITIVE”

The probability that a lab test is POSITIVE,
in the presence of disease

• can use more dilute samples,
  mathmatically: *

True Positives
( True Positives + False Negatives )

Question 24

Diagnostic SPECIFICITY

Answer 24

The probability that a test will be NEGATIVE,
in the absence of disease

mathmatically:

True Negatives
( True Negatives + False Positives )

Question 25

Where do we want the curve to be?

Answer 25

to go UP
Increase True Positive Fraction , SenSITIVITY

To the RIGHT
Decrease False Positive Fraction = Specificity
Increase True Negative Fraction = lower x axis Specificity

Question 26

SenSITIVITY vs Specificity PLOT

Answer 26

Use the calculations for BOTH Sensitivity & Specificity to PLOT

Y = True Positive Fraction (SenSITIVITY)

• Top X** = *False Positive Fraction ( Specificity )
• Bottom X =* True Negative Fraction ( Specificity )

Want the curve to go TOP RIGHT

Question 27

True Negatives >>>>> False Positives
What type of Diagnostic Test do we have?

Answer 27

GOOD Specificity

True Negatives
( True Negatives + False Positives )

Question 28

True Positives >>>>> False Negatives
What type of Diagnostic Test do we have?

Answer 28

Good SenSITIVITY

True Positives
( True Positives + False negatives )

Question 29

What would we like to see in

Test Result Distribution

Answer 29

GOOD SEPERATION

But we typically see overlap ~ 5%

Question 30

Reference VALUES
are determined as……?

Answer 30

RV are deterimined as
AVERAGES** or **a RANGE of values

drawn from a population of usually healthy adults

Question 31

Reference RANGES can be
defined for ……?

Answer 31

RR can be definied for
any CHOSEN population

like adults vs children
Males vs females

Normal range includes 95% of the population
5% will have abnormal test results

Question 32

What are Qualifications in Populated distributions?

distributions may NOT be bell-shaped

Answer 32

Sex / Age

Genetics / FMH

Physiology / Environment / Socioeconomic status

Question 33

Computer-Based AIDS for Error Detection

Answer 33

Comparison of present samples w/ previous samples​

DELTA CHECK
tests for results that vary by a pre-set amount or %

Question 34

Whats is a DELTA CHECK?

Answer 34

Tests for results that VARY by a pre-set amount or %
that is determined by Referencing steps

Most useful for analytes that do NOT vary from DAY to DAY
do not use for analytes that are HIGHLY VARIABLE = glucose

Question 35

Reference Terminology/Steps

Answer 35

Used to detemine the pre-set amount or % in a DELTA CHECK

Individuals make up a
Population from which is selected a
Sample Group on which are determined
Values over which is observed a
Distribution (obvserved value, individual may be compared here)
from which are calculated Limits that may define Intervals

I P S V D L I

Question 36

Analytes that are APPROPRIATE for Delta Check Analysis

Answer 36

Little day to day variation

ELECTROLYTES = Na / K / Cl

Total Protein / Albumin

Urea / Creatinine

Alkaline Phosphatase (only enzyme)

hemoglobin / hematocrit

Question 37

Analytes that are INAPPROPRIATE in Delta check Analysis

Answer 37

may VARY CONSIDERABLY by individuals

GLUCOSE

Phosphate

Enzymes, except alkaline phosphatase

LDH / Creatine Kinase

AST / ALT

Question 38

Common causes of FAILED Delta Checks

Answer 38

Specimin drawn from ABOVE an IV Line
–> dilution, solution upstreme is diluted

Contamination specimen

Mis-Identified specimen

Question 39

Tests that are subject to CYCLICAL VARIATION

Answer 39

ELECTROLYTES = Na / K / Phosphate
Renin / Aldosterone
TSH / PTH
Glucose
Iron / Osteocalcin
Catecholamines

Acid Phosphatase / ACTH / Collagen / Cortison
Gastrin / GH / Prolactin

Question 40

Tests that are Affected by EXERSISE

Answer 40

MUSCLE ENZYMES = CK / ASK / ALT / LDH

Potassium / Phosphate
URIC ACID
BILIRUBIN
Glucose / Gonadotropin / Sex steroids

Cholesterol / TG’s

Question 41

Tests Affected by RECENT Meals

Answer 41

• Sodium / Cholesterol*
• not immediately after a single meal, just over a SEVERAL DAYS*

Gastrin / Glucagon / Insulin

TG’s / urine pH

Cl / Ca / K / P