Lecture 2 – Lab Tests
Labs in Ontario are funded by MOHLTC. Labs are divided into different areas. Turn-around time, cost,
technical expertise, and clinical need are things to consider.
Types of markers:
1. Physiological (normal range in a healthy person, tightly regulated by body)
2. Disease markers (not normally present or only in minute amounts, not regulated by body,
Patient self-testing and point-of-care (POC) testing is convenient, but often costly and lacking in QC.
1. Pre-analytical – patient preparation (e.g. fasting or diet, medications, patient factors such as
age, sex, race, pregnancy, stress), sample collecting, transporting, processing
2. Analytical – sample analysis
3. Post-analytical – interpretation and communication of result
Red cap: serum
Green: plasma + heparin
Grey: plasma + sodium oxalate
Purple: plasma + EDTA
Sampling errors include technique, errors in timing, incorrect sampling site, etc.
Case 1: woman on diuretics shows high serum K+, but physician is not concerned
This is normal range for patients on diuretic medication.
Precise: values agree with each other, but not necessarily close to true value (usually more important)
Accurate: values close to true value
Interferences may decrease precision and accuracy