24 - Fundamentals of Clinical Lab Flashcards
(41 cards)
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 )

