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BioMedChem M3 > 24 - Fundamentals of Clinical Lab > Flashcards

24 - Fundamentals of Clinical Lab Flashcards

1
Q

Difference between

Invasive vs Non-invasive

Tests

A

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

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

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2
Q

Difference between

Analyte vs Biomarker

A

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

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3
Q

Aside from Blood / Urine what are some

Less-Common Samples?

A
  • *Feces**
  • *Occult Blood** test

Sweat
analysis of increased electrolytes for CYSTIC FIBROSIS

Saliva
analysis of drugs / virus / bacteria

Synovial / Cerebrospinal / Amnionic

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4
Q

Common ANALYTES examined in physiological samples

A

Proteins / AA’s / Nitrogen metabolites

Electrolytes / trace elements

Lipids / Enzymes / Hormones

Drugs / Vitamins / small organics

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5
Q

What are some of the Most Common Errors

in Sample Analysis

and how can we avoid them?

A

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*
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6
Q

Pharmacist role in Clinical Labs

A

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

Pharmacists may be involved in:

Sample Collection / Handling

Reporting / Disposal

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7
Q

PRE-Collection Causes of VARIABILITY

in sample colection

A

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
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8
Q

Affect of Supine -> Standing on sample collection

Physiological Variable - Posture

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

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

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9
Q

Affect of UPRIGHT POSTURE on sample collection

Physiological Variable

A

Upright:

Induces LOW SECRETION of Various Hormones:

Catecholamines / Aldosterone / Renin / Others

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10
Q

Affect of Prolonged Bed Rest on sample collection

Physiological Variable

A

Fluid RETENTION

Lower concentrations of PROTEINS

induces elevated NITROGEN EXCRETION

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11
Q

Affect of Brief / Mild Exercise on sample collection

Physiological Variable

A

strenuous exercise -> exaggerated effects of mild exercise

RAISE:

Blood Glucose / Lactate / Several Enzymes

Decrease:

serum TG’s / Cholesterol
can persist for days

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12
Q

Affect of FOOD INGESTION on serum collection

Physiological Variables

A

RAISES levels of many analytes:

Glucose / TG’s

Iron / Sodium / Lactate Dehydrogenase

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13
Q

Blood Collection Technique

Blood has: Plasma / RBC / WBC / Platelets

serum = liquid that seperates when blood clots

A

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*
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14
Q

Difference between

HEPARIN Plasma & SERUM

A

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

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15
Q

Heparin Related ERRORS

A

heparin can displace Thyroxine from serum proteins

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

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

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16
Q

EDTA related ERRORS

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

A
  • *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**
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17
Q

Blood sample POST-Collection Errors

A

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

18
Q

Vacutainer

A

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

19
Q

What are the 3 Types of URINE SAMPLES?

A

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

20
Q

What is a Clean-Catch Specimen?

Urine Samples

A
  • *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)

21
Q

Accuracy is a measure of ?

A

NON-Random / Systematic Error or Bias

How FAR your measurement is
from the TRUE value

22
Q

Precision is the descriptor of?

A

RANDOM VARIATION in a population of data

Ability to produce the same value in REPLICATE testing

23
Q

Diagnostic SENSITIVITY

and its Math value

A

“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 )

24
Q

Diagnostic SPECIFICITY

A

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

mathmatically:

True Negatives
( True Negatives + False Positives )

25
Q

Where do we want the curve to be?

A

to go UP
Increase True Positive Fraction , SenSITIVITY

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

26
Q

SenSITIVITY vs Specificity PLOT

A

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

27
Q

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

A

GOOD Specificity

True Negatives
( True Negatives + False Positives )

28
Q

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

A

Good SenSITIVITY

True Positives
( True Positives + False negatives )

29
Q

What would we like to see in

Test Result Distribution

A

GOOD SEPERATION

But we typically see overlap ~ 5%

30
Q

Reference VALUES
are determined as……?

A

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

drawn from a population of usually healthy adults

31
Q

Reference RANGES can be
defined for ……?

A

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

32
Q

What are Qualifications in Populated distributions?

distributions may NOT be bell-shaped

A

Sex / Age

Genetics / FMH

Physiology / Environment / Socioeconomic status

33
Q

Computer-Based AIDS for Error Detection

A

Comparison of present samples w/ previous samples​

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

34
Q

Whats is a DELTA CHECK?

A

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

35
Q

Reference Terminology/Steps

A

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

36
Q

Analytes that are APPROPRIATE for Delta Check Analysis

A

Little day to day variation

ELECTROLYTES = Na / K / Cl

Total Protein / Albumin

Urea / Creatinine

Alkaline Phosphatase (only enzyme)

hemoglobin / hematocrit

37
Q

Analytes that are INAPPROPRIATE in Delta check Analysis

A

may VARY CONSIDERABLY by individuals

GLUCOSE

Phosphate

Enzymes, except alkaline phosphatase

LDH / Creatine Kinase

AST / ALT

38
Q

Common causes of FAILED Delta Checks

A

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

Contamination specimen

Mis-Identified specimen

39
Q

Tests that are subject to CYCLICAL VARIATION

A

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

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

40
Q

Tests that are Affected by EXERSISE

A

MUSCLE ENZYMES = CK / ASK / ALT / LDH

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

Cholesterol / TG’s

41
Q

Tests Affected by RECENT Meals

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

Gastrin / Glucagon / Insulin

TG’s / urine pH

Cl / Ca / K / P

BioMedChem M3 (8 decks)

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