Week 1 - Intro Flashcards
What is the definition of clinical pathology?
Clinical pathology is the study of disease in the clinical environment by use of laboratory assays.
Clinical pathology = ?
Pattern recognition.
Hematology
* Complete blood count (CBC)
* Blood smear examination
Clinical chemistry
* Biochemistry profile
Coagulation tests
Blood gas analysis
Endocrinology
What should a validity test measure?
A valid test should measure the parameter (“analyte”) of interest over a range of values with minimal interferences.
An abnormal value of an analyte should have ?
a strong association with a disease or condition.
* Few false positive and few false negative results
* Important to establish medical decision limit (cut-off)
value
No laboratory test is _________, and ________ tests are often used in combination to ______ or __________ a disease
perfect, several, diagnose, categorize
Test Sensitivity and Specificity both depend on?
the prevalence of a
disease
True or False: NO test has 100% sensitivity and 100% specificity.
True
There is always a margin of error.
Define test sensitivity.
Sensitivity = ability of a test to detect patients who
truly have a disease (true positives, or TP).
What does a test exhibiting high sensitivity mean?
- Higher sensitivity = a diseased patient is more likely to test positive
If sensitivity of PCR for lymphoma = 91% what does that mean?
- Tested in 100 animals with lymphoma:
- 91% have positive result
- 9% have false negative result
What is important in regards to sensitivity for screening tests?
Important to have high sensitivity for a screening test
* A negative result of a highly sensitive test effectively rules out a disease
Tests with high sensitivity are best used for ?
ruling OUT a disease (“SnOUT”)
Define test specificity.
Specificity = ability of a test to detect patients that
truly do not have a disease (true negatives, or TN)
What does a test exhibiting high specificity mean?
Higher specificity means a non-diseased patient is more likely to test negative
If test specificity is 95%, then out of 100 animals
without the disease?
- 95% of animals will have a negative test result
- 5% of animals will have false positive results
What is important in regards to specificity for confirmatory tests?
Important to have high specificity for a confirmatory test
* Few non-diseased patients will incorrectly test positive (false positive)
Test with High Specificity are best for?
ruling in a disease (“SpIN”)
aka In other words, good for confirming a diagnosis
Sensitive test: when negative result?
rules OUT the disease
Specific test when positive result?
rules IN the disease
Reference intervals
How do we know what values are normal?
Each lab should have its own RI for each species
Each lab should have its own RI (especially based on state, country, etc).
What can be seen below?
Reference interval chart.
Reference Intervals (RI) are established from how many samples?
preferably 60, and ideally 120 samples
In regards to reference intervals, data are?
analyzed and typically fit a normal (Gaussian)
distribution
What do reference intervals represent?
RI represents typical values seen in 95% of healthy animals
How many healthy animals will fall below the RI? Above? Outside?
- 2.5% of healthy animals will be below the RI, and
2.5% of healthy animals above the RI - 1/20 healthy animals will have a result outside of
the RI
Are results within the reference interval range considered to be normal? Explain why or why not?
- Result within the reference interval (WRI), it is not
necessarily “normal” - May not be normal for a given disease process
- Common to have 2 disease processes/pathologic states
“pushing” and “pulling” the result to be within the
reference interval - Do NOT overlook values that aren’t flagged as high
(H) or low (L)!
How can errors in laboratory results occur?
- Errors: instrument/analyzer, reagents, or operator
A pre-analytical error is a result in?
Pre-analytical error: collection of the sample
An analytical error is a result in?
Analytical error: testing the sample
A post-analytical error is a result in?
Post-analytical error: typically human error in reporting results
Quality control programs involve? What does this program consist of?
Involves analyzing quality control materials (QCM) that
have pre-determined concentrations of an analyte
* Typically 3 levels (low, normal, high)
* Each laboratory establishes its allowable error
Quality Control
* Test Precision = same result with multiple
runs?
* Tightly clustered = good precision
* Can be precise, but inaccurate
* Accuracy – mathematical average = true
value?
What information can be used to refine your differential diagnosis list OR be diagnostic?
Signalment, history, physical exam, & lab data
Values ________ the RI may be more significant.
outside
Azotemia + a urine specific gravity indicating that animal is not concentrating urine = ________ disease
renal
Azotemia + concentrated urine = ?
dehydration
Stress leukogram = ?
glucocorticoid (cortisol/prednisone)
What is the first component of a hematology evaluation?
Complete Blood Count (CBC)
Where is blood collected from on an animal?
What needle gauge(s) are typically used?
Where are the veins located?
- Blood is collected from:
- Jugular vein
- Cephalic vein
- Saphenous vein
- values from the artery are different.
- lateral in dogs, medial in cats
- 18- to 22-gauge needle in
small animals
When you want to send out a CBC to the lab, what tube do you put your blood sample into?
A purple top tube which contains anticoagulant.
The anticoagulant in a purple top tube is made up of?
Sodium or potassium EDTA
What is the function of Sodium or potassium EDTA?
Function: chelates calcium and other divalent cations to inhibit
the coagulation cascade –> plasma, not serum
* What’s the difference?
- Plasma contains clotting factors
- Serum does not contain clotting factors
What do automated instruments (hematology analyzers) measure?
- Automated instruments (hematology analyzers)
- White blood cells (WBC): Total WBC count, neutrophils,
eosinophils, basophils, eosinophils, monocytes,
lymphocytes - Red blood cells (RBC): RBC count, hemoglobin,
hematocrit, MCHC, MCH, MCV, +/- reticulocyte count - Platelets: Platelet count
What does the refractometer measure?
Plasma protein
What does heat precipitation/other methods measure?
Fibrinogen
How do automated hematology analyzers measure the hemoglobin concentration? Explain step by step.
- Use spectrophotometry to determine hemoglobin
concentration - The blood sample is aspirated into the analyzer –> chemical agent is added to lyse cells which liberates
hemoglobin - Absorbance of light at a specific wavelength is
proportional to concentration of hemoglobin.
What is the internal quality control check when using an automated hematology analyzer?
General rule as an internal quality control check:
hemoglobin is 1/3 of hematocrit value
* E.g. If hematocrit is 33%, hemoglobin concentration
should be ~11 g/dL
What values do you obtain when using an automated hematology analyzer?
- Mean cell hemoglobin (MCH)
- Mean cell hemoglobin concentration (MCHC)
- Calculated from hemoglobin concentration and
hematocrit - Provides an index for quantity of hemoglobin relative to
volume of packed RBCs: - Hgb (g/dL)/PCV (%) * 100 = MCHC (g/dL)
Describe the electrical impedance (Coulter technology) method for cell counting and sizing?
Describe the flow cytometry method for cell counting and sizing?
more detail re: differentials
How do you obtain a PCV?
- Portion of EDTA whole blood is pulled
into a microhematocrit tube, sealed,
and centrifuged at high speed - After spinning, left with 3 fractions:
- Plasma
- Buffy coat
- WBCs
- Platelets
- Packed erythrocytes
Label this image accordingly.
The PCV should match closely with?
PCV should match closely (within 3%) with
hematocrit generated by the hematology analyzer
How do you measure plasma protein concentration?
- Performed on a spun microhematocrit tube
- Tube is broken between plasma and buffy coat
- Portion of plasma is placed on refractometer glass
5.5
Blood smears should always be made to?
corroborate CBC findings.
Also allows ID of infectious organisms and neoplastic
cells. Disease causing agents will alter results –> be mindful of this.
Describe the blood smear procedure.
- Procedure:
- Use microhematocrit tube to apply drop of blood at frosted edge of glass slide
- Hold spreader slide at a 30 degree angle
- Pull back spreader slide until the blood wicks across
- Rapidly and lightly push the spreader slide to make a smear
What makes up a proper blood smear?
- A properly made blood smear has 3 main
components: - Feathered edge
- Monolayer (cell counting area)
- Body
Label this blood smear image accordingly.
Blood smear staining is similar to which staining properties?
Similar staining properties to hematoxylin & eosin on
histologic specimens
Eosin dye is defined as?
Eosin – acidic dye that stains basic structures red (e.g., red blood cells, eosinophil granules)
Azure dye is defined as?
Azure dye – basic dye that stains acidic structures purple (e.g., nuclei of cells)
Aqueous Romanowsky is?
- Diff Quik
- Commonly used in clinics
Methanolic Romanowsky is?
- Wright-Giemsa
- Commonly used in reference laboratories – a clinical pathologist favorite
