24 - Fundamentals of Clinical Lab Flashcards
Difference between
Invasive vs Non-invasive
Tests
Invasive tests** use a **DEVICE
needle / tubes -> to enter body to collect samples
Noninvasive tests use samples obtained WITHOUT DEVICE
exhaled air / sputum/ urine
Difference between
Analyte vs Biomarker
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
Aside from Blood / Urine what are some
Less-Common Samples?
- *Feces**
- *Occult Blood** test
Sweat
analysis of increased electrolytes for CYSTIC FIBROSIS
Saliva
analysis of drugs / virus / bacteria
Synovial / Cerebrospinal / Amnionic
Common ANALYTES examined in physiological samples
Proteins / AA’s / Nitrogen metabolites
Electrolytes / trace elements
Lipids / Enzymes / Hormones
Drugs / Vitamins / small organics
What are some of the Most Common Errors
in Sample Analysis
and how can we avoid them?
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*
Pharmacist role in Clinical Labs
Interpreting Lab Results
basic grasp of lab terminology / technology / statistics of testing
Pharmacists may be involved in:
Sample Collection / Handling
Reporting / Disposal
PRE-Collection Causes of VARIABILITY
in sample colection
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
Affect of Supine -> Standing on sample collection
Physiological Variable - Posture
- *Supine -> Standing**
- Reduce pt’s blood volume by 10%,*
which in turn INCREASES:
apparent concentration of drugs / enzymes / calcium
Affect of UPRIGHT POSTURE on sample collection
Physiological Variable
Upright:
Induces LOW SECRETION of Various Hormones:
Catecholamines / Aldosterone / Renin / Others
Affect of Prolonged Bed Rest on sample collection
Physiological Variable
Fluid RETENTION
Lower concentrations of PROTEINS
induces elevated NITROGEN EXCRETION
Affect of Brief / Mild Exercise on sample collection
Physiological Variable
strenuous exercise -> exaggerated effects of mild exercise
RAISE:
Blood Glucose / Lactate / Several Enzymes
Decrease:
serum TG’s / Cholesterol
can persist for days
Affect of FOOD INGESTION on serum collection
Physiological Variables
RAISES levels of many analytes:
Glucose / TG’s
Iron / Sodium / Lactate Dehydrogenase
Blood Collection Technique
Blood has: Plasma / RBC / WBC / Platelets
serum = liquid that seperates when blood clots
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*
Difference between
HEPARIN Plasma & SERUM
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
Heparin Related ERRORS
heparin can displace Thyroxine from serum proteins
- -> Falsely HIGH reading
- *thyroid issue**
Heparin salts contain ammonium or lithium
–> falsely HIGH readings of these cations
EDTA related ERRORS
EDTA chelates divalent metal ions = Ca / Fe
inactivates certain enzyes
- *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**
Blood sample POST-Collection Errors
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
Vacutainer
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
What are the 3 Types of URINE SAMPLES?
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
What is a Clean-Catch Specimen?
Urine Samples
- *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)
Accuracy is a measure of ?
NON-Random / Systematic Error or Bias
How FAR your measurement is
from the TRUE value
Precision is the descriptor of?
RANDOM VARIATION in a population of data
Ability to produce the same value in REPLICATE testing
Diagnostic SENSITIVITY
and its Math value
“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 )
Diagnostic SPECIFICITY
The probability that a test will be NEGATIVE,
in the absence of disease
mathmatically:
True Negatives
( True Negatives + False Positives )
Where do we want the curve to be?
to go UP
Increase True Positive Fraction , SenSITIVITY
To the RIGHT
Decrease False Positive Fraction = Specificity
Increase True Negative Fraction = lower x axis Specificity
SenSITIVITY vs Specificity PLOT
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
True Negatives >>>>> False Positives
What type of Diagnostic Test do we have?
GOOD Specificity
True Negatives
( True Negatives + False Positives )
True Positives >>>>> False Negatives
What type of Diagnostic Test do we have?
Good SenSITIVITY
True Positives
( True Positives + False negatives )
What would we like to see in
Test Result Distribution
GOOD SEPERATION
But we typically see overlap ~ 5%
Reference VALUES
are determined as……?
RV are deterimined as
AVERAGES** or **a RANGE of values
drawn from a population of usually healthy adults
Reference RANGES can be
defined for ……?
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
What are Qualifications in Populated distributions?
distributions may NOT be bell-shaped
Sex / Age
Genetics / FMH
Physiology / Environment / Socioeconomic status
Computer-Based AIDS for Error Detection
Comparison of present samples w/ previous samples
DELTA CHECK
tests for results that vary by a pre-set amount or %
Whats is a DELTA CHECK?
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
Reference Terminology/Steps
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
Analytes that are APPROPRIATE for Delta Check Analysis
Little day to day variation
ELECTROLYTES = Na / K / Cl
Total Protein / Albumin
Urea / Creatinine
Alkaline Phosphatase (only enzyme)
hemoglobin / hematocrit
Analytes that are INAPPROPRIATE in Delta check Analysis
may VARY CONSIDERABLY by individuals
GLUCOSE
Phosphate
Enzymes, except alkaline phosphatase
LDH / Creatine Kinase
AST / ALT
Common causes of FAILED Delta Checks
Specimin drawn from ABOVE an IV Line
–> dilution, solution upstreme is diluted
Contamination specimen
Mis-Identified specimen
Tests that are subject to CYCLICAL VARIATION
ELECTROLYTES = Na / K / Phosphate
Renin / Aldosterone
TSH / PTH
Glucose
Iron / Osteocalcin
Catecholamines
Acid Phosphatase / ACTH / Collagen / Cortison
Gastrin / GH / Prolactin
Tests that are Affected by EXERSISE
MUSCLE ENZYMES = CK / ASK / ALT / LDH
Potassium / Phosphate
URIC ACID
BILIRUBIN
Glucose / Gonadotropin / Sex steroids
Cholesterol / TG’s
Tests Affected by RECENT Meals
- Sodium / Cholesterol*
- not immediately after a single meal, just over a SEVERAL DAYS*
Gastrin / Glucagon / Insulin
TG’s / urine pH
Cl / Ca / K / P
