Flashcards in Module 1 - Unit 1 Deck (64)
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?
1. 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.
2. 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.
3. 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.
8. 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
* 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?
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?
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.
The science which deals with the morphology of blood and blood forming tissues
The science that deals with the study of micro-organisms. Subsections include parasitology, virology, and mycology
The science that deals with the blood components and blood typing for the purpose of transfusion
The science that deals with the structure, composition and function of tissue at the cellular level
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
Prevention of disease