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Medical Diagnosis > Lecture 7 (Labs)-Exam 4 > Flashcards

Lecture 7 (Labs)-Exam 4 Flashcards

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USMLE® Step 1 flashcards
1
Q

Reference Range: *
* Established by what?
* What is the sample?
* This means the other 5% outside the range are what?
* Most labs results are what?

A
  • Established by laboratories
  • Healthy non-medicated individuals are sampled and usually through non-parametric analysis the middle 95% dictate the range
  • This means the other 5% outside the range are still healthy individuals, therefore, patients who fall outside the range may potentially be healthy individuals
  • Most lab results are given with a reference range (labeled as abnormal/normal)
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2
Q

Therapeutic range:
* A target range for what?
* What is the therapeutic drug monitoring? Usually drawn when?
* Values below or above this range may indicate what?
* What are example?

A
  • A target range for blood plasma or serum levels of certain medications
  • Therapeutic drug monitoring (TDM) is the clinical practice of measuring specific drugs at designated intervals to maintain a constant centration in a patients blood stream, optimizing that dose
    * Usually drawn when the medication starts and during
  • Values below this range mean inadequate amounts of medication in the blood, plasma, or serum and values above this range may indicate a toxic effect
  • Example: Coumadin (INR), Digoxin (digoxin level), lithium, phenytoin, vancomycin
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3
Q

** Coumadin is what? What is it used for?
* Coumadin decreases what? Reuslts in what?
* Therapeutic range of coumadin is determined by what?

A
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4
Q

INR range and level of anticoagulation differs depending on what?

A

depending on the indication for its use
* Atrial Fib: INR 2-3
* DVT/PE: INR 2-3
* Mechanical heart valve: 2.5-3.5

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5
Q

Range-less tests:
* For certain laboratory tests, the presence of disease is associated with what?
* What are the 3 examples?

A

For certain laboratory tests, the presence of disease is associated with a value that is above a certain threshold

Example:
* Troponin – marker for myocardial infarction (should be 0)
* Illicit drugs- cocaine, cannabis,meth(+ or -)
* ETOH level

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6
Q

Sensitivity and specificity:
* Many diseases have a ”gold standard” or “benchmark test” which generally centers on what?
* What is sensitivity and specificity?
* They will always be what?
*

A
  • Many diseases have a ”gold standard” or “benchmark test” which generally centers on diagnostic yield ( how well the test correctly identifies diseased subjects as positive and non-diseased subjects as negative)
  • Sensitivity and Specificity are two statistical measures most commonly used to assess the performance of an alternative test against the gold standard
  • They will always be inversely related (one increases, one decreases)
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7
Q
  • What is sensitivity?
  • Tests with high sensitivity are good tests used to what?
  • Measures what?
A
  • Sensitivity (true positive rate) – quantifies how well a test identifies true positives (how well a test can classify subjects who truly have the condition of interest) – how well a test can rule out disease
  • Tests with high sensitivity are good tests used to screen, if there is a low sensitivity than there can be a high percentage of false negatives
  • Measures the proportion of subjects with an actual positive outcome who are correctly given a positive assignment
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8
Q

What is the equation for sensitivity?

A
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9
Q

Sensitivity example:
* In a study completed on prostate cancer, measuring PSA with a new technique, 489 subjects were identified as true positives and 10 subjects were false negatives, corresponding to a sensitivity of what?

A

98%. (489/ (489 +10))
* Another way to say it – 98% sensitivity indicates that 489 out of 499 subjects with clinically significant prostate cancer were correctly identified as positive using the PSA cut off designated in the study – thus the new testing was found to correctly identify 98% of all subjects with clinically significant prostate cancer

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10
Q
  • What does specificity quantifies what?
  • What does specificity measure?
A
  • Specificity (true negative) quantifies how well a test identifies true negatives ( how well a test can classify subjects who truly do not have the condition of interest)
  • Specificity measures the proportion of subjects with an actual negative outcome who are correctly given a negative assignment
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11
Q

What is the specificity equation?

A
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12
Q

263 subjects were identified as true negatives and 1400 subjects were false positives, corresponding to a specificity of what?

A

16% ( 263/ (1400 + 263))
* A 16% specificity indicates that 263 out of 1663 subjects without clinically significant prostate cancer were correctly identified as negative using the PSA cutoff, thus the study was found to correctly identify 16% of all subjects without clinically significant prostate cancer

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13
Q

Sensitivity and specificity are highly relevant statistical parameters for assessing what?

A

Sensitivity and specificity are highly relevant statistical parameters for assessing the performance of a diagnostic test, however, it is often more meaningful to predict whether a person will truly have the disease based on a positive or negative test result

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14
Q

Positive predictive value and negative predictive value reflect what? What does it answers?

A

Positive predictive value and negative predictive value reflect the proportion of positive and negative results that are true positives and true negatives
* šEX: positive predictive value answers the question “If I have a positive test, what is the probability that I actually have the disease?”
* Negative predictive value answers the question, ”if I have a negative test, what is the probability that I actually don’t have the disease?

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15
Q

Positive and negative predictive value will change with what?

A

Positive and negative predictive value will change with disease prevalence – the more common the disease the more sure we can be that a positive test really indicates disease, etc.

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16
Q

What are the positive and negative predictive value equations?

A
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17
Q

list the terms

A
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18
Q
A
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19
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A
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20
Q

Explain what this means?

A
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21
Q

What does this mean?

A
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22
Q

What is prevalence and incidence?

A
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23
Q

What does precision and accuracy mean?

A
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24
Q

When can the different errors occur?

A

Errors can occur in the pre-analytical phase (most errors occur during this phase), analytical phase (less common), and post-analytical phase

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25
Q

Pre-analytical phase:
* Encompasses what?
* What are the types?

A
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26
Q

Analytical phase:
* What is this?
* What are the errors?

A
  • Time that the sample is being analyzed in the laboratory
  • Errors are less frequent due to high level of automation in the lab

Possible errors:
* Incorrect use of the instrumentation
* Use of expired reagents
* Testing wrong patients blood

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27
Q

What is post-analytical phase? What are the examples?

A
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28
Q

How do you pick what test to order?

A
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29
Q

Blood tubes:
* What do the tops mean?
* Many tubes contain what?

A
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30
Q
A
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31
Q

What happens with clotting tests?

A

Clotting of the blood makes blood cell counts and coagulation tests impossible because the clotting factors are consumed in the clot and the blood cells become trapped in it

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32
Q

The amount of anticoagulant in the light blue-top tube must be in a specific proportion to the blood volume in the tube, What is it? What happens if it is not that ratio?

A
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33
Q

Blood facts-KNOW

  • Bood consititutes how much of total body weight?
  • Blood consist of what?
  • What does plasma make up of?
  • What is serum?
  • What is the solid portion?
A
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34
Q

What are the functions of blood (4)

A
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35
Q

What happens to the blood with centifugation?

A
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36
Q

Plasma:
* Plasma collected is frozen within when?What is the shelf life?

A

Plasma collected is frozen within 24 hours to preserve the functionality of the various clotting factors and immunoglobins
* Has a shelf life of 1 year

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37
Q

What are the different products derived from plasma (4)

A
38
Q

Platelet rich Plasma (PRP)
* What is it used for? (3)

A
  • Dermatology – anti-aging treatments, lip injections
  • Ortho - used to treat tendon, ligament, muscle, and cartilage injuries and early OA goodstudies
  • Male pattern baldness
39
Q

What is serum? What is plasma?

A

Serum is the liquid that remains after the blood has clotted
* Used for testing purposes, culture mediums

Plasma is the liquid that remains when clotting is prevented with the addition of an anticoagulant

40
Q

What does -cytosis and -penia mean?

A
41
Q

CBC:
* Evalutes what? Why does it vary?
* What is it used for?

A
  • Evaluates all blood cells in circulation – looks at cells in whole blood (RBC’s, Hgb, Hct, WBC, platelets)
    * Reference values for the CBC vary across the life cycle and between genders (neonates, infants, children, adults)
  • Is used to diagnose multiple conditions such as anemia, infection, leukemia, platelet dysfunction, bone marrow dysfunction
42
Q

What are the indications for CBC (5)?

A
  • An essential component of a complete physical exam
  • Suspected hematologic disorder
  • History of hereditary hematologic disorder
  • Suspected infection
  • Monitoring undesired drug side effects that may cause dyscraias
43
Q

What are the different componetns of CBC?

A

RBC (Red blood cells)
* MCV
* MCH
* MCHC

Hemoglobinš
Hematocrit
Platelets (thrombocytes)
RBC morphology

44
Q

What does RBC indicates?

A

used in identifying and classifying anemias

45
Q

What is MCV?

A

MCV (mean corpuscular volume) – this indicates the volume of the Hgb in each RBC
* šClassified as normocytic, microcytic, macrocytic

46
Q

What is MCH?

A

MCH (mean corpuscular hemoglobin) – the weight of the Hgb in each RBC
* šNormochromic, hypochromic, and hyperchromic

47
Q

What is MCHC?

A

MCHC (mean corpuscular hemoglobin concentration) – proportion of Hgb

48
Q

What is RBC morphology?

A

involves examination of RBC’s under a microscope to compare the actual appearance of the cells with the calculated values for RBC indices
* Cells are examined for abnormalities in color, size, shape, and content

49
Q

RBCs: Erythrocyte count
* What is it?

A

Number of RBC’s per cubic millimeter – expressed as the number of RBC’s per liter of blood

50
Q

What are conditions what can decrease RBCs?

A
51
Q

What are conditions what can increase RBCs?

A
52
Q

Hemoglobin:
* What is it responsible for?
* What is it made up of?
* Normal hemoglobin is made of a combo of what?

A
  • The protein contained in red blood cells that is responsible for delivery of oxygen to the tissues
  • It is made up of iron (heme) and protein (globin)
  • Normal hemoglobin is made of a combination of alpha and non alpha globin chains
53
Q

What are the 3 main types of normal hemoglobin in adults?

A
  • Hgb A: makes up 95-98% of adult hemoglobin
  • Hgb A2: makes up 1-3% of adult hemoglobin
  • Hgb F: majority of neonatal hemoglobin, but 2-3% in normal adults
54
Q

Hemoglobin as a diagnostic tool:
* To ensure what?

A

To ensure adequate tissue oxygenation, a sufficient hemoglobin level must be maintained

55
Q

Diagnostic purposes:
* What does it mean when the hgb is low?
* What is hemoglobin electrophoresis?

A
56
Q

Thalassemia:
* Group of disorder caused by what?
* Production can be what?
* The imbalance of globin chain production impairs what?

A
  • Group of disorders caused by abnormal production of globin chains
  • Production can be diminished or can be absent for one of more of the globin chains
  • The imbalance of globin chain production impairs the production of normal hemoglobin
57
Q

What are the two types of thalassemia?

A
58
Q

Hematocrit:
* What does it measures?
* Reported as what?

A
  • HCT measures the volume of packed red blood cells relative to whole blood š
  • Reported as a percentage
59
Q

What are conditions with higher hematocrit?

A
  • Newborn babies that gradually decreases during the neonatal period
  • Adult males show higher HCT than adult females
  • In high altitude, the number of RBC becomes high due to persistent hypoxia
60
Q

What are conditions with lower hematocrit?

A
  • Anemia
  • Pregnancy due to hemodilution
61
Q
  • What does spherocytes indicate?
  • What do bite cells indicate?
A
  • Spherocytes: immune hemolytic anemia (Direct antiglobulin test DAT+) vs. hereditary spherocytosis (DAT-)
  • Bite cells: G6PD deficiency
62
Q
  • What does target cells indicate?
  • What does schistocytes indicate?
  • What does acanthrocytes indicate?
A
  • Target cells: sickle cell anemia, hemoglobinopathy or liver disease
  • Schistocytes: Sickle cell anemia, TTP/HUS, DIC, prosthetic valve, malignant HTN
  • Acanthocytes: liver disease
63
Q

What are the componts of RBC indices?

A
64
Q

What is RDW?

A

variation in the size of red cells can be quantified and expressed as red cell distribution width (RDW) or as red cell morphology index. Expressed as a percentage

65
Q
A
66
Q
  • What is the mcc of anemia?
  • Patients present with what?
  • Most patients experience some symptoms related to anemia when the hemoglobin is what?
A
67
Q

What is EPO? What happens when a pt has low hgb?

A

Erythropoietin (EPO), is made in the kidney, is the major stimulator of RBC’s
* šAn individual with low hemoglobin has elevated levels of EPO, except under those patients with renal failure

68
Q

Mechanisms involved in anemia (3)

A

Blood loss, hemolytic anemia, deficient/defective erythropoiesis

69
Q

Mechanisms involved in anemia

What are the two types of blood loss?

A
  • Acute- hemorrhage, surgery, trauma, menorrhagia
  • šChronic- heavy menstrual bleeding, chronic gastrointestinal blood losses [6] (in the setting of hookworm infestation, ulcers, etc.), urinary losses (BPH, renal carcinoma, schistosomiasis)
70
Q

Mechanisms involved in anemia

What are the two types of hemolytic anemia?

A
  • Acquired- immune-mediated, infection, microangiopathic, blood transfusion- related, and secondary to hypersplenism
  • šHereditary- enzymopathies, disorders of hemoglobin (sickle cell), defects in red blood cell metabolism (G6PD deficiency, pyruvate kinase deficiency), defects in red blood cell membrane production (hereditary spherocytosis and elliptocytosis)
71
Q

What are the 3 types of deficient/defective erythropoiesis?

A
  • Microcytic
  • šNormocytic, normochromic
  • Macrocytic
72
Q
A
73
Q

Iron studies:
* Depletion of iron stores may result from what?
* Adults older than 50 with iron deficiency and GI bleeding needs to be worked up for what?

A
  • Depletion of iron stores may result from blood loss (GI bleeding), decreased intake, impaired absorption, or increased demand
  • šAdults older than 50 years of age with iron deficiency and GI bleeding need to be evaluated for malignancy
74
Q

Tests for iron:
* What does serum iron measure?
* What does serum ferritin measure?
* What does transferrin measure?
* What does TIBC measure?
* What does iron saturation calculate?

A
  • Serum iron – measure the iron in your blood
  • šSerum ferritin- measure the amount of stored iron in your body š
  • Transferrin – measures how well your body transports iron in your blood
  • Total Iron binding capacity (TIBC) – another way to measure how well your body transports iron
  • Iron saturation – calculation to find percentage of your transferrin that is saturated with iron
75
Q

Transferrin:
* What is it synthesis inversely proportional to?
* Levels will increase when? Low?

A
76
Q

When is TIBC increased?

A

Increased in iron deficiency as there are more available binding sites for iron

77
Q
A
78
Q

WBCs:
* What is the term WBC?
* Part of what?
* Participates in both what?
* Helps diagnose what?

A
79
Q

What are granulocytes?
What are agranulocytes?

A

Granulocytes:
* Neutrophils, basophils, eosinophils

Agran:
* Lymphocytes and monocytes

80
Q

What are the different CBC?

A

Differential v non-differential
* Diff: includes breakdown of specific leukocyte components

81
Q

Platelets:
* What are they?
* Initation of activity begins with what?
* Maintain hemostais by what?

A
82
Q

Cause of thrombocytopenia (low platelets) -three

A
  • Consumption: your bone marrow makes enough platelets but your body destroys them or uses them up
  • Lack of production: bone marrow does not make enough platelets
  • Your spleen holds on to too many platelets-> šWrong shape
83
Q

What are the causes of thrombocytopenia, consumption?

A
  • Disseminated intravascular coagulation (DIC), auto immune destruction of platelets (immune thrombocytopenia- ITP), aplastic anemia, cancer, infection, heart valves/bypass surgery
  • Allergy – Heparin induced thrombocytopenia (HIT)
84
Q

What are the causes of thrombocytopenia, lack of production?

A
  • šExposure to toxic chemicals
  • šETOH consumption
  • Certain medications
85
Q

Platelet dysfunction
* What are the multiple lab tests?
* The complex cascade involved in what?
* Most well known as what?
* What are teh otehr drugs?

A
86
Q

RBC morphology
* Completed with what?
* Usually doe when?
* In general red cells have what?

A
  • Completed with a peripheral blood smear
  • Usually done when there is an unexplained anemia, leukopenia, splenomegaly, CML, malignancies
  • In general red cells have a fairly uniform variation in size, with a red cell distribution width of 11- 15% in normal individuals
87
Q

What is it called when abnormal variation is size?
* Differentials of microcytic anemias include?
* Normocytic anemia occurs when?
* macrocytes are seen in ?

A
88
Q

What is poikilocytosis

A

Abnormal variation in shape

89
Q
A
90
Q
A
91
Q
A

Medical Diagnosis (16 decks)

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