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24 Cards in this Set
- Front
- Back
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Two reasons for ordering lab tests pre-diagnosis
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1. Screening for disease
2. Diagnosis of Disease |
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Two reasons for ordering lab tests post-diagnosis
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1. Monitor Treatment
2. Evaluate Prognosis |
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Four ways lab tests impact patient care
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1. Reduce length of stay in ED
2. Optimize treatment 3. Decrease unnecessary admissions 4. Reduce inpatient length of stay |
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Bayes' Theorem
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RP=(IP X TPR) / (IP X TPR) + {(1-IP) X (1-TNR)}
RP=Revised Probability IP=initial probablity TPR=True pos rate TNR=True neg rate |
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Sensitivity definition
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True Positive Rate
The percentage of patients with a positive result from a population with the disease |
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Specificity definition
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True negative result-
The percentage of patients with a negative test in a population without the disease |
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False positive rate
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1 - specificity
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False negative rate
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1 - sensitivity
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Rules out diagnosis
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SNOUT: High sensitivity + negative result
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Rules in diagnosis
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SPIN: High specificity + positive result
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Good for screening tests
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High sensitivity
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Good for confirmation tests
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High specificity
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Likelihood Ratio Calculations
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LR+ = Sensitivity / (1 - Specificity)
LR- = (1-Sensitivity) / Specificity |
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Likelihood Ratio Application
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=1 is a coin toss
>10 or <0.1 large and often conclusive shifts in posttest probablility 0.5-2 small, rarely important shift in probability |
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Positive predictive value
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= TP / (TP+FP)
OR = a / (a+b) |
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Negative predictive value calculation
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= TN / (FN+TN)
OR = d / (c+d) |
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Sensitivity calculation
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= TP / (TP+FN)
OR =a / (a+c) |
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Specificity calculation
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= TN / (FP+TN)
OR = d / (b+d) |
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True value confidence interval calculation
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True Value = Mean +/- Z X SD/sq root N
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How are differences in a patient's test results interpreted?
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<5-10% no change
10-19% possible change 20% probable change |
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In therapeutic drug monitoring if the trough value is high what action should be taken?
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Reduce dose
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In therapeutic drug monitoring if the peak value is low what action should be taken?
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Increase dose
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What are possible sources of error in lab testing?
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Patient preparation
Hemolysis, Lipemia, Icterus IV contamination Methodological Charting errors |
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Avoid the Ulysses Syndrome
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Order only tests likely to help in diagnosis!
Def: The ill effects of extensive diagnostic testing due to a false-positive result in the course of routine laboratory screening. |
