Lecture 4 Laboratory Test Stewardship

Question 1

What can be some issues when it comes to ordering laboratory tests for patients, and why should we think about the context of if they need the test or not?

Answer 1

approx 30% of tests are repeated inappropriately

is cost of test worth the info it generates?

Logistical issues for pt: fasting or dietary restrictions, transportation - collected sample (ex. 24 hour urine for creatinine clearance), to the lab (vehicle, parking, scheduling collection, etc)

Question 2

What are things to consider when thinking about point of care (POC) testing for patients?

Answer 2

A. obtain informed consent from pt

B. testing environment - appropriate for collecting sample, conducting test, device and supply storage, hazardous waste disposal, privacy for pt

C. choice of POCT (informed choice among tests based on understanding of test characteristics) - type of test (quantitative or qualitative), sample required (saliva, blood, urine), test performance (sensitivity, specificity, etc), pt population, cost

D. routine practice - hand hygiene, PPE, specimen handling, routine cleaning and decontamination procedures, procedures in event of accidental exposure to blood or body fluids

Question 3

What are important aspects to look at when interpreting lab results?

Answer 3

accuracy and precision, test performance - sensitivity and specificity, positive and negative predictive values

reference range, critical value, units

Question 4

What does sensitivity refer to in the context of laboratory test values?

Answer 4

ability of the test to correctly identify people who truly have a given condition ⇒ if test has high sensitivity it has a high possibility of a true positive and low possibility of a false negative

Question 5

What does specificity refer to in the context of laboratory test values?

Answer 5

ability of the test to correctly identify people who truly do not have a given condition

if test has high specificity it has a low possibility of a false positive and high possibility of a true negative

Question 6

What are predictive values for laboratory test results?

Answer 6

provides clinically meaningful info for individual pt care

Positive Predictive Value (PPV) - % of positive results that are truly positive, ex. if test is + what is prob that pt actually has disease

Negative Predictive Value (NPV) - % of negative results that are truly negative, ex. if test is - what is prob the pt actually doesn’t have disease

Question 7

What are reference ranges when it comes to laboratory test results?

Answer 7

range of values obtained from testing large sample of ‘healthy’ individuals - plot distribution of values

this will contain 95% of values

lower and upper limits are not absolute but reflect threshold beyond which the benefits of a therapeutic intervention increase,, may vary from lab to lab

Question 8

What are critical values in context of laboratory test results?

Answer 8

test result that is beyond reference range and requires immediate attention

rule out collection or lab error first, how far is this value beyond range, are the pt sx consistent with value