Refernce Interval

Question 1

When interpreting laboratory data, clinicians compare the measured test result from a patient with a ________

Answer 1

reference interval.

Question 2

The theory for the development of reference intervals was the work of

Answer 2

2 main expert committees

Question 3

These committees established 4 things which are?

Answer 3

the importance of standardizing collection procedures,

the use of statistical methods for analysis of reference values

estimation of reference intervals

the selection of reference populations.

Question 4

Reference interval is defined as?
Example, the reference interval for glucose is?

The lower value is referred to as the ______ and the upper limit is referred to as the ______

Answer 4

A pair of medical decision points that span the limits of results expected for a given condition.

3.5mmoles/L to 5.6 mmoles/L.

lower reference limit
Upper reference limit

Question 5

The upper and lower reference limits are set to include a specified percentage _______ of the values for a population
This means that a percentage ______ of patients will?

Answer 5

(usually 95%)

Usually 5%

fall outside of the reference interval in the absence of any condition or disease.

Question 6

Reference intervals are sometimes erroneously referred to as?

All _____ are ______ but not all _____ are ______

Answer 6

Normal ranges

While all normal ranges are in fact reference intervals, not all reference intervals are normal ranges.

Question 7

Reference intervals are sometimes referred to as?;

Answer 7

reference ranges;
the preferred term is reference interval because range implies the absolute maximum and minimum values

Question 8

Reference intervals are usually established by the _______ or the _______

Answer 8

scientific community or
the manufacturers of reagents and new methodologies.

Question 9

The clinical laboratory is required by good laboratory practice and accreditation agencies (eg? checklist)
to either verify or establish reference intervals for any new tests or significant changes in methodology.

Answer 9

College of American Pathologists [CAP]

Question 10

The two main types of reference interval studies that are reviewed in this lecture are

Answer 10

(1) establishing a reference interval

(2) verifying a reference interval.

Question 11

Establishing a reference interval: A new reference interval is established when there is no _____or _______ in the clinical or reference laboratory with which to ________

It is a costly and labor-intensive study that will involve laboratory resources at all levels and may require from _____ to ____study individuals.

Answer 11

no existing analyte or methodology
conduct comparative studies.

120 to as many as >700

Question 12

Verifying a reference interval aka

This is done to confirm ______ for an analyte using the same (identical) type of analytic system (method and/or instrument).

These are the most common reference interval studies performed in the clinical laboratory and can require as few as ___ study individuals

Answer 12

Transference

the validity of an existing reference interval

20

Question 13

CLSI means

Answer 13

Clinical and Laboratory Standards Institute

Question 14

When possible, clinical laboratories rely on _________or ___________to determine reference intervals.
This avoids the expensive and lengthy process of establishing a reference range interval on a minimum of 120 healthy people.

Answer 14

assay manufacturers or on published primary literature

Question 15

The CLSI allows less vigorous studies to verify a reference interval with as few as 20 subject specimens.
Method verification studies can be used if________& _________ are similar to the vendor’s reference data and package insert information.

Answer 15

the test method and study subjects

Question 16

The main assumption in using transference studies is that ______ & _______ are similar.

Answer 16

the reference method is of high quality and the subject populations

Question 17

The manufacturer’s reported 95% reference limits may be considered valid if no more than ____of the tested subjects fall outside the original reported limits
If more than _% of the values fall outside of the proposed interval, an additional ___ or more specimens should be analyzed.

Answer 17

10%

20

Question 18

If the second attempt at verification fails, the laboratorian should re-examine the analytic procedure and identify any differences between ________&________[

Answer 18

the laboratory’s population and the population used by the manufacturer for their analysis.

If no differences are identified, the laboratory may need to establish the reference interval using at least 120 individuals.
Once a reference interval is determined, it needs to be communicated to the physicians interpreting test results at the time the test results are reported.
This is important given the slight variations in reference intervals seen even among testing facilities using similar methodologies.

Question 19

To establish a reference range study
10 things must be done. These are

Answer 19

1. Define an appropriate list of biological variations and analytic interferences from medical literature.
2. Choose selection and partition (e.g., age or gender) criteria.
3. Complete a written consent form and question-naire to caoture selection criteria.
4. Categorize the potential reference individuals based on the questionnaire findings.
5. Exclude individuals from the reference sample group based on exclusion criteria.
6. Define the number of reference individuals in consideration of desired confidence limits and statistical accuracy.
7. Standardize collection and analysis of reference specimens for the measurement ot a given analyte consistent with the routine practice of patients
8. Inspect the reterence value data and prepare a histogram to evaluate the distribution of data.
9. Identify possible data errors and/or outliers and then analyze the reference values.
10. Document all of the previously mentioned steps and procedures

Question 20

Possible exclusion factors for a reference interval study

Answer 20

Fasting or nonfasting
Genetic factors
Drugs: prescription or over the counter
Pregnancy
Illiness, recent
Exercise pattern

Question 21

Possible subgroups requiring partitions for a reference interval study

Answer 21

Age (adult and childhood)
Fasting or nonfasting
Diet
Stage of pregnancy
Sex
Tobacco use

Question 22

Pre analytical considerations for reference interval studies

Answer 22

Subject preparation
Prescription medications
Collection time
Sample storage
Stress
Food/beverage ingestion

Question 23

Analytical considerations for reference interval studies

Answer 23

Precision
Accuracy
Lot-to-lot reagents
Linearity
Interference
Recovery

Question 24

The reference interval is calculated statistically using methods that depend on the distribution of the data.
In the most basic sense, data may be either be _______ or _______. With aka

Answer 24

normally distributed (gaussian)

skewed (nongaussian)

Question 25

If reference data are normally distributed, the reference interval can be determined using a _____method.

Answer 25

parametric

Question 26

A parametric method defines the interval by the mean

this formula will include the central 95% of values as given in the example shown.
In reality, most analytes do not display a normal (gaussian) distribution.

Answer 26

+/- 1.96 SDs;

Question 27

Data that are not normally distributed (i.e., nongaussian) must be analyzed using _____ analyses.

Answer 27

nonparametric

Question 28

Nonparametric determination of the reference interval is analyzed using?, which do not depend on the distribution.

The reference interval is determined by using the central 95% of values; the reference range is therefore defined by _____to ______percentiles.

Answer 28

Percentages

the 2.5th to the 97.5th

Question 29

To calculate the interval, values are ranked from lowest to highest and the 2.5th and 97.5th percentiles are then calculated as follows:

Answer 29

n= number of reference specimens

2.5th percentile = 0.025(n+1)

97.5th percentile = 0.975(n+1)

Question 30

Most reference interval analyses are determined using ______ analysis.
Why?

Answer 30

nonparametric

This is because nonparametric analysis can be used on gaussian distributed data and it is the CLSI-recommended method

Question 31

With the development of statistical software packages such as(list 6) reference intervals are rarely determined manually.
However, it is important to understand how basic statistical concepts are used by the software to generate their analyses.

Answer 31

EP Evaluator,
MedCalc,
GraphPad Prism,
Minitab,
JMP, and
SAS/STAT,

Question 32

Measures of Center
The three most commonly used descriptions of the center are the ? Define them

Answer 32

mean, the median, and the mode.

The mean is most commonly used and often referred to as the average.
The median is the “middle” point of the data and is often used with skewed data.
The mode value that occurs the most frequently

Question 33

The mode is rarely used as a measure of the data’s center but is more often used to describe data that seem to have _____

Answer 33

two centers (i.e., bimodal).

Question 34

Mean is calculated by

Answer 34

Summing the observations/ number of observations

Question 35

The median is the middle of the data after

Answer 35

the data have been rank ordered.
It is the value that divides the data in half.

For example, given a sample of 5, 4, 6, 5, 3, 7, and 5, rank order the points: 3, 4, 5, 5, 5, 6, 7. Because there are an odd number of values in the sample, select the middle value: 5.

Given another sample with an even number of values: 5, 4, 6, 8, 9, and 7, again rank order the points: 4, 5, 6, 7, 8, 9. Select the two “middle” values: 6 and 7. Then add them: 6 +7= 13; and divide by 2: 13/2= 6.5.

Question 36

The mode is the?

Answer 36

most frequently occurring value in a dataset.

Although it is seldom used to describe data, it is referred to when in reference to the shape of data, a bimodal distribution, for example.

In the sample: 3, 4, 5, 5, 5, 6, and 7, the value that occurs most often is 5. The mode of this set is then 5.

Question 37

After describing the center of the dataset, it is very useful to indicate how the data are distributed (spread).
This is known as

Answer 37

Measure of Dispersion

Question 38

The spread represents the relationship of all the ______ to the _____

There are three most commonly used descriptions of spread:

Answer 38

data points to the mean.

1) range,
(2) Standard deviation(S.D),
(3) coefficient of variation (CV).

Question 39

The range is simply?

Answer 39

the largest value in the data minus the smallest value, which represents the extremes of data one might encounter.

Question 40

Standard deviation (also referred to as ____,_____,_____)

It is the________ measure of variation.

Answer 40

“s,” SD, or σ

most frequently used

Question 41

SD describes?.
Formula for SD:

Answer 41

the distribution of all data points around the mean

Square root of summation of (individuals - mean)2
/
n-1

Question 42

Another way of expressing SD is in terms of the CV.

Answer 42

Coefficient variation

Question 43

The CV is calculated by

Answer 43

dividing the SD by the mean and multiplying by 100 to express it as a percentage:

Question 44

The CV simplifies comparison of SDs of test results expressed in?
Analytes measured at different concentrations can have a drastically different SD but a comparable CV.

Answer 44

different units and concentrations.

Question 45

There are many different “shapes” datasets can exhibit; the most commonly discussed shape/distribution is the?(

Answer 45

gaussian distribution

also referred to as normal distribution)

Question 46

The gaussian distribution describes many continuous laboratory variables and shares several unique characteristics;

Answer 46

The mean, median, and mode are identical;

The distribution is symmetric
(meaning half the values fall to the left of the mean, and the other half fall to the right)

the symmetrical shape is often referred to as a “bell curve.”

Question 47

The total area under the gaussian curve is ____or ____
Much of the area——under the “normal” curve is between +/-1 SD
Most of the area——under the “normal” curve is between +/-2 SDs
And almost all of the area—%— under the “normal” curve is between +/-3 SDs

Answer 47

1.0, or 100%.

68.3%

95.4%

99.7%

Question 48

The 68-95-99 rule

Answer 48

given any gaussian distributed data:

Approximately 68% of the data fall between +/-1 SD from the mean;
Approximately 95% of the data fall between +/-2 SDs from the mean; and
Approximately 99% fall between +/- 3 SDs from the mean.

Question 49

The Gaussian distribution

Answer 49

This found application in the reference interval section.
Many patient data are not normally distributed.
These data may be skewed or exhibit multiple centers (bimodal, trimodal, etc.)
Plotting data in histograms such as these are an easy way to visualize distribution.
However, there are also mathematical analyses (e.g., normality tests) that can confirm if data fit a given distribution.
The importance of recognizing whether data are or are not normally distributed is related to the way it can be statistically analyzed.