Reference Intervals

Vocabulary flashcards based on lecture notes about Reference Intervals.

Evidence-Based Pathology and Laboratory Medicine

The conscientious, explicit, and judicious use of current best evidence in making decisions about the care of individual patients.

Null Hypothesis

There is no difference between the two populations.

P-value

A measure of the probability that an event or parameter measured from a study group is significantly different from the value in the control group.

Validity

The ability of the test to distinguish between those with the disease and those without.

Sensitivity

The ability to identify those that do have the disease.

Specificity

The ability to correctly identify those who do not have the disease.

Positive predictive value

If the result of the test is positive what is the probability that the patient has the disease.

Negative predictive value

If the result of the test is negative what is the probability that the patient does not have the disease.

Reference intervals

Range of measurements for a specific analyte from a population of representative healthy individuals.

Decision level/limit

Particular cut-off value for an analyte that enables individuals with a disorder or disease to be distinguished from those without the disorder or disease.

Partitioning criteria

Characteristics of a reference population that can allow them to be divided into significant subclasses.

Parametric Analysis

Statistical analysis for normally distributed data.

Non-parametric Analysis

Data - non-Gaussian distribution, the central 95% of the data can be determined by ordering the array from the lowest to the highest values and eliminating the lowest and highest 2.5% = rank order analysis

One sided reference interval

If clinical interest is only in “low” or “high” results, one-sided intervals exclude only the 5% of the population in the “abnormal” tail of the distribution

Outliers

Reference values that arise from a different population of test results and lie well outside the majority of reference values.

Dixon’s test

Statistical technique for identifying an outlier.

Block procedure

A test to identify outliers when 2 or 3 outliers exist on one side of the distribution

Tukey’s procedure

A statistical procedure to find outliers for gaussian distributed data using the middle 50% of the sample.

IQR

Interquartile range: Q3 – Q1

Validation

The process of defining an analytical requirement and confirming that the method under consideration has performance capabilities consistent with that requirement.

Verification

Procedures to test to what extent the performance data obtained by the manufacturers during method validation can be reproduced in the environment of the end- user.

In house IVD

An in vitro medical device that is: within the confines or scope of an Australian Medical Laboratory or Australian medical laboratory network

In vitro diagnostic medical device (IVD)

means a medical device that is a reagent, calibrator, control material, kit, Specimen receptacle, software, instrument, apparatus, equipment or system, whether used alone or in combination with another diagnostic product for in vitro use

Sensitivity (equation)

TP / (TP + FN)

specificity

TN / (FP + TN)

Positive predictive value (equation)

TP / (TP + FP)

Negative predictive value (equation)

TN / (FN + TN)

EBLM

Evidence Based Laboratory Medicine

Selection bias

Bias due to using samples of convenience

Performance bias

Systematic differences in the care provided apart from the intervention being evaluated

Attrition bias

Systematic differences between groups in withdrawals from a study

Detection bias

Systematic differences between groups in how outcomes are determined

Publication bias

the tendency for journals to publish positive findings more often than negative or ambiguous ones

What should reference values be established or verified by?

The laboratory on the local patient population

For normally distributed data, how many standard deviations encompasses 95% of results?

1.96

How to calculate the lower 2.5th percentile in rank order calculation

r1 = 0.025(n + 1)

How to calculate the upper 97.5th percentile in rank order calculation

r2 = 0.975(n + 1)

D

The absolute difference between the extreme observation and the next observation

R

The range of all observations, including extremes

If In house IVDs are separated into how many groups?

Two

What does EBLM ensure?

testing is carried out that is relevant, informative and based on appropriate test cohorts