Module 1 - Unit 1 Flashcards
Define test sensitivity
is defined as the number of positive test results (expressed as a per cent) obtained on patients with the disease. A test that is 100% sensitive, has no false negatives and therefore appropriately identifies all the diseased population.
Sensitivity =( TP/(TP+FN)) x 100
Define test specificity
is defined as the number of negative test results (expressed as a per cent) obtained on patients without the disease. A test that is 100% specific has no false positives and correctly classifies the healthy population.
Specificity = (TN/(TN+FP)) x 100
Define test efficiency
Efficiency of a test is defined as the percentage of patients correctly classified by the test.
Efficiency of a test = ((TP+TN)/(TP+TN+FP+FN)) x 100
Define predictive value of a positive result
Predictive value (PV) of a positive test result is defined as the number of true positive results obtained as a percentage of all positives. Predictive Value Positive Result = (TP/(TP+FP)) x 100
Define predictive value of a negative result
Predictive value of a negative test result is defined as the number of true negative results obtained as a percentage of all negatives.
Predictive Value NegativeResult = (TN/(TN+FN)) x 100
Define false positive rate
False positive rate is defined as the number of false positives obtained as a percentage of all negatives.
False Positive Rate = (FP/(TN+FP)) x 100
How would an increase in prevalence affect the predictive value of a positive result and the predictive value of a negative result
as prevalence increases, the predictive value of a positive test result increases and the predictive value of a negative test result decreases;
What is a discriminator?
Disriminator values are reference values determined by studying patient test results in a patient population with a specific disease. This type of analysis is most often applied in screening programs and /or critical ER type algorithms.
A discriminator is a single test value that is different from the test values established by statistical means as reference interval.
Explain how a Levy-Jennings graph is derived and what function it serves in a clinical chemistry laboratory.
For each method, Levy-Jenning charts (example below) are produced for both normal and abnormal quality control material. The Levy-Jenning graphs display the mean and +/- 2 S.D. on the y-axis and the day on the x-axis.
With reference to the urinalysis laboratory exercise in Unit 1 of the Case History Manual, please list the potential pre-analytical errors that could affect the quality of a patient’s test result.
Exercise can increase creatine kinase, AST, HDL, lactate, uric acid
· Diet can affect test results. High protein diets can lead to increased uric acid, ketones, and urea. Caffeine affects catecholamine levels. Moderate alcohol consumption can increase HDL.
· Most laboratories require the patient to fast overnight prior to being collected.
· If the patient is dehydrated, test analytes such as blood urea nitrogen (BUN), total protein, sodium, and hemaocrit can be elevated due to the hemoconcentration.
· Posture or patient position during specimen collection can affect certain test results such as aldosterone, catecholamines, and renin.
What strategies are used in the laboratory to assess the quality of the patient test results in the post-analytical phase of the testing cycle?
- Test patterns/grouping:
Many tests respond to a disease process in the same way. For example, in renal failure it is usual that an elevated creatinine level is accompanied with an elevated urea nitrogen. Therefore, this pattern could be used to assess an elevated creatinine value. An elevated creatinine value is likely correct if the urea nitrogen is also elevated. - Comparing test result to previous results:
One of the many advantages of a computerized laboratory information system (LIS) is the ability to automatically flag patient results based on their previous test results. In an LIS system a delta per cent flag can be set for each test based on expected physiological and analytical variation. For example, if the delta for glucose is set at 20%, then the system would automatically compare the current patient glucose result with the previous and if the difference is greater than 20 %, the current result would be flagged and the technologist would need to assess and override the flag. - Relating the patient’s test result to diagnosis:
Does the reported patient test result fit the clinician’s clinical assessment of the current patient health status? The laboratory should welcome feedback from clinicians or nurses as an important component of its internal quality control program.
- Describe the types of errors that can affect the quality of the patient’s test result in the pre-analytical phase of the testing cycle.
- Requisition errors can lead to the improper patients being collected, improper test being performed, improper timing of specimen collection. Most laboratories will have procedures in place that require proper identification of patient prior to collection.
- Improper collection technique such as increased tourniquet time (affect: increase total protein, iron, lipids) , improper cleaning agents (isopropyl alcohol should not be used for ethanol testing ), improper draw site (draw should be from below the intravenous site) can affect test results.
- Type of sample required. Most laboratories have policies regarding specimen types (vacutainer collection tube) required for each test. Inappropriate vacutainer could lead to test errors.
- Improper handling of specimen from the unit to the laboratory can affect test results. Light can affect tests such as bilirubin vitamin A, B12 and temperature affects blood gas, ammonia , and lactate results.
What are the 6 steps of the patient care cycle?
1- Individual becomes aware of problem 2- Individual seeks medical care 3- Clinician seeks objective data to establish diagnosis 4- Laboratory test performed 5- Laboratory test interpreted 6- Therapy implemented and evaluated
During the 2nd step of the patient care cycle, the clinician will perform an interview and an examination. What types of information are they going to be seeking?
Onset of symptoms Present illness Past History Family History Vital signs
- more on page 5 of manual*
True or false
Approximately 80% of patients are diagnosed based on the information gathered from the presenting signs and symptoms?
TRUE
What is the percentage of cases where the clinician will order some laboratory test ( further testing)?
2 out of 10 ( 20%)
What are the 3 types of diagnosis?
1- Differential diagnosis
2- Provisional diagnosis
3- Definitive diagnosis
What is a differential diagnosis?
is a list of the most probable disease entities that could give rise to the patient’s complaints
What is a provisional diagnosis?
after the clinician has had time to reflect, he or she can make a provisional diagnosis from the list of possible disease entities outlined in the differential diagnosis.
Can the patient be treated conservatively by a provisional diagnosis until it is confirmed?
YES
There will be further testing done to confirm
What is a definitive diagnosis?
established by confirmatory data such as laboratory test, biopsy, radiological examination etc. The clinician established the diagnosis with certainty by carrying out further objective tests.
What is the primary goal of the laboratory?
to do that RIGHT test as accurately as possible on the RIGHT patient in an appropriate time frame in order to affect a positive patient outcome.
Define Hematology
The science which deals with the morphology of blood and blood forming tissues
Define Microbiology
The science that deals with the study of micro-organisms. Subsections include parasitology, virology, and mycology
Define immunohematology
The science that deals with the blood components and blood typing for the purpose of transfusion
Define histology
The science that deals with the structure, composition and function of tissue at the cellular level
Define cytlogy
The science that deals with the study of cells, their origin and structure
Define Clinical Chemistry
The applied science that utilizes assembled knowledge from biochemistry, chemistry, biology, physiology, and molecular biology
What are the purposes of clinical chemistry?
Detection of disease Determination of the diagnosis Evaluation of the extent and severity of disease Monitor treatment Prevention of disease Research
What are the main subspecialties associated within clinical chemistry?
- endocrinology
- immunology
- enzymology
- toxicology
What kind of information is required in the ordering process?
(from a clinician to the lab)
1- patient demographic data
2- Clinical information
3- Test information
4- Ordering physician
IF the laboratory had access to the patients chart, what could be improved?
- improved test utilization
- reduce test duplication and repeats
- improve testing strategies utilize in patient care maps or clinical pathways.
(in the future, they will have access)
What does the term accurate refer too?
how close a test result is to the true answer
What are the 3 phases of the testing cycle?
1- pre-analytical
2- analytical
3- post -analytical
In which phases do the largest proportion of errors occur?
Pre and Post Analytical phases.
The pre-analytical variables can be grouped into what 3 categories?
- patient preparation
- specimen collection and handling
- interferences
What are the established criteria that are used by clinical chemist in the proper selection of equipment and methods?
The methods must be specific for the desired constituent you want to measure (minimal or no chemical interferences), analytically sensitive ( measure very low concentrations of constituent) have an analytical range that is clinically relevant and be reproducible.
What is the objective of a quality control system in clinical chemistry?
Assess the precision (reproducibility) and accuracy ( true value) of the analytical procedures in current use for the purpose of patient testing and reporting of results.
What does the Levy-Jennings graph display?
the mean and +/- 2 SD on the y-axis and the day on the x-axis
What percentage of all points should fall between the +/- 2 SD ?
95%
What % of points should fall between +/- 1 SD?
66%
In the post-analytical phase, how is component of the quality control program i=to review the patient results done?
1- Test patterns/groupings
2- Comparing test result to previous results
3- Relating the patient’s test result to diagnosis
- see. p. 19 for more explanation*
What are the major factors associated with normal physiological variations between individuals?
1- inter-individual ( sex, age, race, diet)
2- intra-individual ( time of day)
3- diurnal ( social environment, and diet)
What is reference intervals?
it is defined as a set of values of a certain type of quantity from and individual or group of individuals corresponding to a stated description
Define False Positive (FP)
result that incorrectly classifies a non diseased patient in the diseased population
Define False Negative (FN)
result that incorrectly classifies a diseased patient in the healthy population
Define True Positive (TP)
result that correctly classifies a diseased patient in the diseased population
Define True Negative (TN)
result that correctly classifies a non diseased patient in the non diseased population
What are discriminator values?
they are reference values determined by studying patient test results in a patient population with a specific disease
a discriminator is a single test value that is different from the test values established by statistical means as reference intervals
True or False
As prevalence increases, the predictive value of a positive test result increases and the predictive value of a negative test results decreases?
TRUE
True or False
As prevalence decreases, the predictive value of a negative result decreases and the predictive value of a positive result increases?
FALSE
As prevalence decreases, the predictive value of a negative result increases and the predictive value of a positive result decreases
True or False
at any fixed prevalence, and increase in specificity result in an increase in the predictive value of a positive result?
TRUE
True or False
at any fixed prevalence an increase in sensitivity results in an increased in the predictive value of a negative result?
TRUE
What is the formula for Likelihood Ratio (LR)?
LR = sensitivity / false positive rate.
What are critical values diced to help with?
Aids the clinician in reaching a quick assessment in patients presenting with high clinical risk, and taking appropriate action
What are examples of the kinds of action that could be prescribed during the last step of the patient cycle (Therapy and Evaluation)
- drug therapy
- surgery
- special diet
- exercise
Can the laboratory be used to monitor the effectiveness of therapy?
Yes
Why do we need laboratory medicine?
- provide biochemical information for the management of pt. health
- provide objective data to aid in decision -making
- confirm diagnosis
prognosis
monitory
screening
True or False
Data is always useful
FALSE
it is only useful if it is RELIABLE
Define “mean”
The average, measure of central tendancy
-Value around which all values congregate
How do you get the mean?
Add all values together and divide baby the total number of values
Define “Variance”
- A measure of the spread of the data
- How spread out is the range of values compared to the mean value
Where can specimens be collected in the human body
- Urine
- CSF
- Tissue
- Saliva
- Facal matter
- Semen
how do you calculate the coefficient of variation?
CV = SD x 100/ mean
