24 - Fundamentals of Clinical Lab Flashcards by Karlo Sison

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

Common ANALYTES examined in physiological samples

Proteins / AA’s / Nitrogen metabolites

Electrolytes / trace elements

Lipids / Enzymes / Hormones

Drugs / Vitamins / small organics

How well did you know this?

Not at all

Perfectly

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*

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

Affect of UPRIGHT POSTURE on sample collection

Physiological Variable

Upright:

Induces LOW SECRETION of Various Hormones:

Catecholamines / Aldosterone / Renin / Others

How well did you know this?

Not at all

Perfectly

Affect of Prolonged Bed Rest on sample collection

Physiological Variable

Fluid RETENTION

Lower concentrations of PROTEINS

induces elevated NITROGEN EXCRETION

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

Affect of FOOD INGESTION on serum collection

Physiological Variables

RAISES levels of many analytes:

Glucose / TG’s

Iron / Sodium / Lactate Dehydrogenase

How well did you know this?

Not at all

Perfectly

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*

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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**

How well did you know this?

Not at all

Perfectly

Blood sample POST-Collection Errors

Study These Flashcards

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

Study These Flashcards

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?

Study These Flashcards

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

Study These Flashcards

*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 ?

Study These Flashcards

NON-Random / Systematic Error or Bias

How FAR your measurement is
from the TRUE value

Precision is the descriptor of?

Study These Flashcards

RANDOM VARIATION in a population of data

Ability to produce the same value in REPLICATE testing

Diagnostic SENSITIVITY

and its Math value

Study These Flashcards

“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

Study These Flashcards

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? ## Footnote *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**

24 - Fundamentals of Clinical Lab Flashcards

(41 cards)