Question 1

Endocrinologists typically encounter patients with hormonal abnormalities such as Cushing's disease (i.e., hyperadrenocorticism).Which of the following attributes is the most desirable for laboratory tests utilized in this environment?

Accepted Answer

Laboratory tests with the highest sensitivity are the most desirable in situations where patients have a disease that is serious, should not be misdiagnosed, and is treatable.Cushing's disease can be fatal if misdiagnosed.However, if diagnosed, Cushing's disease is treatable.

Question 2

Considering normal reference intervals utilized, ______ percent of the time, well (healthy) patients will fall outside this range, and ______ percent of the time, well (healthy) patients will fall within this range.

Accepted Answer

The reference interval is defined as the interval between and including two numbers, an upper and lower reference limit.These two numbers are statistically determined to include the middle 95% of values for the population from which the subjects have been drawn.This will leave 5% of individuals in this population that fall outside the reference interval.

Question 3

Some medical facilities are known for their cerebrovascular centers that provide immediate care for stroke victims.Which of the following attributes is the most desirable for laboratory tests utilized in this environment?

Accepted Answer

Laboratory tests with the highest efficiency are the most desirable in situations where the disease is serious but treatable, and false-negative and false-positive results are equally serious or damaging.In the case of stroke, time is extremely important.False negatives may delay necessary immediate treatment, which may have serious consequences.False positives can result in equally serious situations where unnecessary treatment for stroke can lead to hemorrhage.

Question 4

Which of the following statements correctly compares and contrasts a-priori and a-posteriori methods of reference individual selection?
1)In both methods, exclusion and partitioning take place after sampling and analyte testing.
2)A-priori methods require fewer reference individuals to be studied than a-posteriori methods.
3)Questionnaires for potential reference individuals must be more detailed for a-posteriori methods than for a-priori methods.

Accepted Answer

The a-priori method of selecting reference individuals is a method that is best suited for use with laboratory methods that are established and well studied.There is less background research associated with this method, because much information is already known about it.Thus well-defined exclusion and partitioning criteria can be established before the selection of reference individuals.Because of this background and knowledge regarding these methods, fewer samples are required for the development of the reference interval; essentially, the number of samples necessary for the results to be statistically valid.The a-posteriori method is more useful for new or poorly studied laboratory methods.With less information being known about these methods, research must be more extensive, although the literature typically contains little information.Thus the questionnaire for this method must be more extensive, and a larger number of samples will be required.Also, in this method, exclusion and partitioning of participants usually occurs after sampling and analysis.

Question 5

Which of the following laboratory considerations are not necessary factors to consider for the transfer of a reference interval from one laboratory to another?

Accepted Answer

Postanalytical considerations have little influence on laboratory test results and are not necessary for reconciliation before transference of reference intervals.Both preanalytical and analytical considerations must be reconciled before transference of reference intervals.

Question 6

In establishing a reference interval, data are plotted on normal-probability paper, and the resulting line curves away from linearity at the upper portion of the plot.What is the next step that should be taken in determining the reference interval?

Accepted Answer

The parametric method used for determining reference limits is based on the assumption that the observed values follow a normal (or Gaussian) distribution.If such data are plotted on normal-probability paper, normally distributed data will appear as a straight line.If curvature is present in this plot, the next step would be to plot the data on log-probability paper in an attempt to transform the data into a Gaussian distribution.If this step is successful, data are said to follow a log-normal distribution and can be used to determine the reference interval.

Question 7

Which of the following best explains why the phrase reference interval is preferred over the phase normal interval when associated with clinical laboratory test results?

Accepted Answer

The word normal has several different meanings in laboratory medicine that can cause confusion.One use is associated with a Gaussian, or "normal," distribution.Additionally, the word normal is frequently associated with the interval of laboratory results suggesting health.The confusion with this use of normal is that intervals of laboratory results are also established for disease, or stages of disease.("Normal interval for disease" seems contradictory.) Other meanings of normal include common, frequent, usual, and typical, all of which may be used in referring to laboratory test results.Thus for clarity, the phrase reference interval should be used in defining laboratory intervals for health or disease (i.e., "reference interval for health" or "reference interval for disease").

Question 8

Reference interval determinations should follow the guidelines established by:

Accepted Answer

The Clinical and Laboratory Standards Institute (CLSI, previously the National Committee for Clinical Laboratory Standards [NCCLS]) has published guidelines for determining valid reference values and reference intervals.Only in situations where it may be difficult to collect data from the recommended number of reference individuals should variations be seen.

Question 9

Which of the following best describes the analysis of samples to establish reference intervals for a new laboratory method?

Accepted Answer

It is important that reference intervals reflect the laboratory and population for which the interval will be utilized.The population issue will be addressed by the appropriate method to select individuals from which the interval will be determined.To address the laboratory issue, run-to-run variations, reagent lot-to-lot variations, and technologist-to-technologist variations are important components that must be incorporated into the study protocol.To incorporate these variables, samples must be analyzed over a period of several days.

Question 10

Which of the following attributes is the most desirable for a laboratory test utilized in the diagnosis of diseases such as cystic fibrosis that are currently not curable?

Accepted Answer

Laboratory tests with the highest specificity are the most desirable in situations associated with diseases such as cystic fibrosis that are serious and not curable.In this situation, false positives could lead to serious psychological or economic trauma to the patient, mandating the use of a test with the highest specificity.

Question 11

It has been shown that significant differences between the standard deviations of subclasses of subjects, even when the means are identical, can lead to deviations in diagnostic sensitivity and diagnostic specificity for disease detection.Thus in these situations, there may be the need for separate reference intervals.What statistical test should be selected to determine the need for different reference intervals in this situation?

Accepted Answer

The z-test evaluates the statistical significance of the difference between subclass means through the utilization of the standard deviation of each subclass.If a significant difference is determined by the z-test, separate reference intervals should be determined.

Question 12

To construct receiver-operating characteristic curves, which of the following plots is prepared?

Accepted Answer

A receiver-operating characteristic curve is prepared by plotting the sensitive (i.e., the true-positive rate) of the test versus 1-sensitivity (i.e., the false-positive rate).

Question 13

An urologist's office has a high likelihood of encountering patients with prostate cancer.Which of the following attributes is the most desirable for laboratory tests utilized in this environment?

Accepted Answer

Laboratory tests with a high predictive value for a positive test are essential in a situation where treatment of a false positive may have serious consequences.False positives when testing for prostate cancer can result in removal of the prostate or treatment to destroy the prostate, both of which have very serious consequences.

Question 14

The process of separating reference intervals based on criteria such as age, sex, and race, as well as statistical analysis showing significant differences between these subclasses, is known as:

Accepted Answer

Partitioning is the process of separating reference intervals based on criteria such as age, sex, and race, as well as statistical analysis showing significant differences between these subclasses.It is generally assumed that when the difference between the observed means of two subclass populations is statistically significant, each subclass warrants its own reference interval.Before the laboratory proceeds with partitioning, it is important to consult the clinicians in the field to determine the appropriate clinically significant difference.

Question 15

Which of the following steps should be taken when an outlier value is obtained during data collection for the determination of reference intervals?

Accepted Answer

When data for determining reference intervals fall outside the expected distribution, it is important to determine the statistical significance of the outlying value.There are several statistical techniques that can be utilized for this purpose.NCCLS guidelines support the use of the one-third cutoff value method of Reed, Henry, and Mason to evaluate for statistically significant outliers.By this method, if the absolute difference between an extreme observation and the next largest (or smallest) observation is equal to or greater than one third of the range of all observations (including the outlier), the extreme observation is deleted.

Question 16

CLSI guidelines recommend that the reference interval be estimated by the nonparametric method and that a minimum of _______ reference values be utilized for reference-interval determination.

Accepted Answer

It is recommended by the Clinical and Laboratory Standards Institute (CLSI) that a minimum number of 120 reference values be used to establish reference intervals.

Quiz 24: Reference Intervals and Clinical Decision Limits

Endocrinologists typically encounter patients with hormonal abnormalities such as Cushing's disease (i.e., hyperadrenocorticism) .Which of the following attributes is the most desirable for laboratory tests utilized in this environment?

Considering normal reference intervals utilized, percent of the time, well (healthy) patients will fall outside this range, and percent of the time, well (healthy) patients will fall within this range.