Lab Test Stewardship

Question 1

read Pharmacy Practice Standards

& Laboratory Tests

Answer 1

HPA (Schedule 19, Section 3(1))
“In their practice, pharmacists promote health and prevent and treat diseases, dysfunction and
disorders through proper drug therapy and non-drug decisions.”

ACP
Standard 3: Pharmacists must consider appropriate information from each patient. (eg. renal fxn test to adjust dose)
3.5 Information that may be required under Standard 3.4(j) includes:
e) laboratory values
Standard 6: Dispensing a Schedule 1 drug pursuant to a prescription
Standard 13:Prescribing in an emergency
Standard 14:Prescribing at initial access or to manage ongoing therapy

Question 2

read ACP standard on POCT

Answer 2

“When an interaction with a patient or consideration of patientspecific information indicates that a pharmacist should review laboratory data, and the data is not available, the pharmacist must order the appropriate test, refer the patient to an appropriate regulated health professional to evaluate the need that a test be
ordered, or if appropriate, conduct a Point of Care Test (POCT)

Question 3

what do you need to order a lab test (3)

– Edmonton Zone (DynaLIFE Medical Labs)
– Calgary Zone (Calgary Laboratory Services)
– North, Central, and South Zones (AHS Laboratory Services)

Answer 3

– Practitioner ID to register with the laboratory, Need practiicioner ID to prove you are a regulated HCP
– Be familiar with the standards and responsibilities*
– A plan for receiving and interpreting the results
• 24/7 contact information (critical results will be phoned to the ordering practitioner), need to contact the person who ordered it ASAP

Question 4

what are some issues with ordering lab tests

Answer 4

• 30% of laboratory tests in Canada are repeated inappropriately
• T4 and TSH, don’t need to do both
  Logistical issues for the patient
  – Fasting or dietary restrictions
  – Transportation
  • Collected sample (e.g., 24 hour urine collection for creatinine clearance)
  • To the laboratory (vehicle, parking, scheduling collection, etc)

Question 5

Specimen Collection for a Laboratory Test

what fluids are mose commonly used for analysis?

Answer 5

• Blood and urine are the most common body fluids used for analysis
• The amount of specimen required, storage container, and timing of collection will depend on the type of laboratory test
  – Creatinine clearance*
  • Urine 24 hour collection (container)
  • Blood 5 mL tube used for estimation

Question 6

Why Order a Laboratory Test? (4)

Answer 6

1. Ensure the drug and dose are appropriate for the patient
   – Therapeutic drug monitoring
   – Interpreting culture and sensitivity to confirm the correct antibiotic is used
2. Monitor the patient’s response to therapy
   – Does the white blood cell count decrease in response to an antibiotic
   – Is the blood glucose responding to addition of a new antihyperglycemic drug
   – Is the thyroid responding to a change in dose
3. Monitor for adverse effects and ensure the patient’s safety
   – What is the patient’s renal function
   – Does serum creatinine change significantly when a drug known to affect the kidneys (e.g., NSAID, ACE
   inhibitor) is added
4. Screening of patients with preliminary indicators for untreated diseases
   – Diabetes risk
   – Confirm a suspected illness (e.g., strep throat)

Question 7

at what point of pt care process do lab tests occur?

Answer 7

any point of pt care process

Assessment, if they’re reaching their goals, implemeting or f/u

Question 8

Accuracy vs precision

Answer 8

• Accuracy – how close is the test value to the ‘true’ value
– Influence of both random and systematic error
• Precision – how close are the values if the test is repeated

both properties monitored and reported by the
laboratories

Question 9

• If we assume the test result is an accurate and precise description of what is happening in the patient, the next step is to interpret what the test result means

what does positive test? negative test?

Answer 9

– Positive: suggests disease is present

– Negative: suggests disease is absent

Question 10

define Sensitivity

• if a test has high sensitivity, what does it mean?

- low possibility of a ________

Answer 10

Ability of the test to correctly identify individuals who have a given condition
– If a test has high sensitivity…
• We can be quite confident that someone with a positive result has the condition we are looking for
• Low possibility of a false negative
⟹ negative result can be used to rule out the condition (SnOUT)
– If a test has low sensitivity…
• A positive result could lead to over treatment

Question 11

define Specificity

• if a test has high Specificity, what does it mean?

- low possibility of a ________

Answer 11

• Ability of the test to correctly identify individuals who do not have a given condition
– If a test has high specificity…
• We can be quite confident that someone with a negative result does not have the condition we are looking for
• Low possibility of a false positive
⟹ positive result can be used to rule in the condition (SpIN)
– If a test has low specificity…
• A negative result could miss identifying the condition

Question 12

see slides for equations on calculating sensitivity and specificity

Answer 12

ok
Sensitivity = True Positive/Patients with Disease
Specificity = True Negative/Patients without Disease

Question 13

Predictive Values
Considers prevalence of condition in the population,
sensitivity, and specificity

what is Positive Predictive Value (PPV)?
Negative Predictive Value (NPV)?

Answer 13

PPV = % of Positive results that are Truly Positive
NPV =  Negative results that are Truly Negative

PPV = true pos/all positive tests
NPV = true neg/all neg tests

Question 14

Reference Range

- contains ___% of the values

Answer 14

Range of values obtained from testing a large sample of ‘healthy’
individuals
– Plot the distribution of values
• The reference range will contain 95% of the values
- The lower and upper limits are not absolute, but reflect a threshold beyond which the benefits of a therapeutic intervention increase

Question 15

T/F: the Reference Range may vary from laboratory to

laboratory

Answer 15

True

Question 16

Critical Values

• 3 things to consider

Answer 16

• Test result that is beyond the reference range and requires immediate attention
– Rule out collection or lab error first
– How far is the ‘critical value’ beyond the reference range
– Are the patient’s symptoms consistent with the lab value

eg. Potassium concentration 7.5 mmol/L and presence of peaked T
waves

Question 17

Laboratory Units

what units do Canadian labs use

Answer 17

International System of Units (SI)
– Standardized, metric-based system for reporting
– Examples: mmol/L, mEq/L

Question 18

5 steps to interpret lab tests

Answer 18

1. Gather information about the patient
2. If relevant laboratory data is not available, request or order the laboratory test
3. Compare the laboratory value to the reference range
4. Assess the laboratory value within the context of the patient’s symptoms, medical conditions, other factors that can influence the result
5. Determine if the laboratory result requires action

Question 19

what does the ACP guidance doc say?

Answer 19

Obtain informed consent from the patient
Testing environment: supply storage, disposal, privacy
Selection of the POCT: type of test, sample requeired, cost, pt pop, test performnce
Routine practice: hygiene, PPE, cleaning, specimen handling

Question 20

see quiz 2 question

Answer 20

When the test is positive…

We are more concerned with specificity than with sensitivity of the test
We can be very confident the patient has an infection from streptococcus if the possibility of a false positive is very low (as in this example). In other words… a positive test result can be used to rule in the condition (Recall the acronym: SpIN - a test with high Specificity with a positive result can be used to rule IN the condition of interest)

When the test is negative…

We are more concerned with sensitivity than with specificity of the test
We can be very confident the patient DOES NOT have an infection from streptococcus if the possibility of a false negative is very low (however, in this example the possibility is 45%).