LMP301H1 Lecture Notes - Lecture 1: Hyponatremia, Hyperglycemia, Respiratory Acidosis

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14 Sep 2016
Introduction to the Biochemistry of Human Disease
Lecture 1 - Introduction
Disease - sickness with characteristic symptoms; response to injury
A diagnosis of disease requires objective evidence
Biochemical tests use body fluids, are relatively non-invasive, safe, and fast and accurate
Objectives of laboratory medicine
1. Define (diagnosis)
2. Predict (prognosis)
3. Monitoring
4. Find cause (etiology)
5. Screening
Mortality: causing death or reducing lifespan
Morbidity: impairs quality of life
Prevalence: number of cases of disease in a population
Incidence: number of new cases/unit time in a population
Endemic: most of the population has the disease
Epidemic: widespread occurrence of disease in a population where it’s rare
Classifications of disease:
Hereditary genetic etiology
Congenital - from birth
Injury physical or chemical stress
Infections often bacterial or viral
Nutritional caused by diet
Metabolic abnormal production of enzymes/other molecules
Purpose of testing:
Diagnostic testing
Screening for risk of a disease (e.g. heart disease, cancer)
Exclusion test
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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,
normally excreted)
Patient self-testing and point-of-care (POC) testing is convenient, but often costly and lacking in QC.
Testing process:
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
Specimen type:
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
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Lecture 3 Cases
The normal interval is the central 95% of a distribution from a healthy sample of 120+ individuals.
However, factors such as age, sex, and race may differ the best healthy range is the patient’s own.
This 95% interval = 2.8 x [(analytical variance)2 +(biological variance)2]
Test interpretation:
True positive
True negative
False positive
False negative
o Where true/false determines whether the test was right and positive/negative
determine the test result.
Clinical sensitivity = TP/(TP+FN)
Detects a disease when it is actually present
SnNout = SeNsitivity test, Negative result, rule OUT disease
Clinical specificity = TN/(TN+FP)
Detects absence when the disease is not present
SpPin = SPecificity test, Positive result, rule IN disease
Predictive value of + test = TP/(TP+FP)
Probability of test detecting a disease when it’s present
Predictive value of test = TN/(TN+FN)
Probability of test detecting absence when it’s absent
Efficiency = TP+TN/(TP+TN+FP+FN)
Accurately make a conclusion
Receiver operator characteristic (ROC) curves balance sensitivity and specificity
y-axis = true positive rate (sensitivity)
x-axis = false positive rate (1-specificity)
upper left corner is best
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