Pathology: Selecting and Interpreting Laboratory Tests

Question 1

Reference interval

Answer 1

The central 95% of test values for a population of healthy individuals which characteristics comparable to those of the patient (reference population)

Question 2

Substances that behave as normal distributions (4)

Answer 2

o Sodium
o Potassium
o Calcium
o Albumin

Question 3

Creatinine- reference limit trends (3)

Answer 3

• Limits are higher in men than women
• Limits are lower for pregnant women than non-pregnant women
• Limits are inappropriately high for patients with muscle wasting/amputation

Question 4

Creatinine levels reflect

Answer 4

• glomerular filtration rate

Question 5

Serum alkaline phosphatase- reference limit trends (3)

Answer 5

• Limits are higher in children
• As children mature, drop in levels occurs at an earlier age in females than males bc epiphyseal plate closes sooner in females than males
• Upper limit of reference interval for elderly adults should be raised 30-50% above the usual adult reference interval

Question 6

False positive can be due to (4)

Answer 6

• Inappropriate reference interval
• Interference with the analysis
• Physiological factors
• Statistical abnormality

Question 7

Conditional probabilities are (4)

Answer 7

• The pre-test probability of the disease
• The sensitivity of the test for the disease
• The specificity of the test for the disease
• These conditional probabilities allow calculation of the post-test probability for either a positive or a negative test result

Question 8

Sensitivity- definition

Answer 8

The probability of a positive test result if the disease is present

Question 9

Specificity-definition

Answer 9

The probability of a negative test result in the absence of the disease

Question 10

Bayes’ Theorem

Answer 10

The concept that the interaction of sensitivity, specificity, and pre-test probability determines the diagnostic probability or predictive value of a test result

Question 11

Positive results for tests where pre-test probability of disease is low are more likely to be

Answer 11

false positive than true positive results

Question 12

Use of lab tests in medical diagnosis can be divided into 3 categories:

Answer 12

• Discovery
• Confirmation
• Exclusion

Question 13

Discovery test- requirements (4)

Answer 13

• High sensitivity
• Most patients with the disease should have a positive test result if the test is effective to screen for the disease
• Low rate of false negatives
• Specificity is desirable, but not essential

Question 14

Confirmation test- requirements (3)

Answer 14

• Specificity of 100% for the disease
• No false positives
• Post-test probability of 100%

Question 15

Exclusion test- requirements (3)

Answer 15

• Sensitivity of 100% for the disease
• All patients with the disease must have a positive test result
• NO false negatives

Question 16

Excluding disease requires a

Answer 16

sensitive test

Question 17

Confirming disease requires a

Answer 17

specific test

Question 18

Accuracy

Answer 18

The closeness of the test result to the actual or true concentration of the substance being analyzed

Question 19

Precision (2)

Answer 19

• The reproducibility of test results on a given specimen

- Expressed as CV

Question 20

Questions to ask (4)

Answer 20

1. Is this test result normal or abnormal
2. How should I interpret a positive or negative result
3. What test should I order
4. Can I rely on the results of the test

Question 21

First step in laboratory tests appropriately is

Answer 21

To define the question to be answered or the decision to be made