W1 - Reference Ranges, Sensitivity and Specificity

What is the basic reference range?

The expected range of values of an analyte in a healthy population

What is the FULL definition of a reference range?

The statistically defined range of a constituent pattern or parameter measured in an adequate sample of subjects of specified age and sex in the absence of detectable disease and measured by a specified method

What is the purpose of a reference range?

• Help physician make a diagnosis

• Monitor the disease progress

• Used as a guide to therapy

• To assess the health status of a patient

What are some factors why each labs needs to establish their own reference values?

• Age population

• Sex

• Race

• Diet

• Blood Group

• Geographic location

• ect

What are the NCCLS guidelines in establishing a reference value?

• A list of biological and analytical variable that might interfere with the test

• Criteria for selecting well, normal individuals

• Excluding subjects not meeting the criteria

• Prepare subjects properly

• Collect & handle specimens properly and consistently

• Analyze specimen under well defined, controlled condition

• Inspect resulting reference data and prepare a histogram

• Select appropriate statistical methods and analyze the data

• Document all steps above

What is the test used to assess a Gaussian histogram?

Kolmogorov-Smirnov Test (KS Test)

What is the minimum # of data needed for a gaussian distribution?

40 (Use ± SD as the reference interval)

What is the minimum number of data for a nonparametric distribution?

120 (Use the mid 95% of results as the reference interval)

What is True Positive? (TP)

A sick patient who has a positive test

What is a True Negative (TN)?

A well patient has a negative test results

What is a False Positive? (FP)

A well patient who has a positive test results

What is False Negative (FN)?

A sick patient who has a negative test results

What is sensitivity?

The % of sick patients who test positive

What is Specificity?

The % of well people who test negative

What is Predictive value(+)?

The probability that a positive test results predicts the patient has the disease

What is Predictive value (-)?

The probability that a negative test results predicts the patient does not have the disease

What is Efficiency?

The percent of test results that reflect the patients actual state of wellness or sickness

What is the equation for efficiency?

E = ((TP+TN)/TOTAL)*100

What is Prevalence (of disease)?

The number of people in a population having the disease

What is the equation for prevalence?

P = ((TP + FN)/Total)*100

When would you want the highest sensitivity?

• When the disease is serious and should not be missed

• When the disease is treatable

When would you want the highest specificity?

• When the disease is serious but not treatable or curable

• Knowing the disease is absent has public health or psychological value

What is the equation for sensitivity?

Sen = (TP/(TP+FN))*100

What is the equation for Specificity?

Spec = (TN/TN+FP))*100

What is the equation for predictive value (+)?

P(+) = (TP/(TP+FP))*100

What is the equation for Predictive value (-)?

P(-) = (TN/(TN+FN))*100