Clinical Biochem 1 Flashcards
Differentiate between invasive and non-invasive tests? risk?
Invasive
- examines fluid or tissue by using a needle, tube, device or scope to penetrate skin/enter body
- pose some risk to patients
Non-invasive
- does not require skin penetration or an instrument entering the body
- minimal risk
Differentiate between accuracy & precision
Accuracy
- mean measure is close to the true value (not always close with each other)
Precision
- Agreement of results when test is run many times on the same sample
- Not always accurate or close to mean value
Define sensitivity
What does a high sensitivity indicate? Calc?
- identify positive results in patients WITH the disease
- true positive rate % with patients who actually test positive
Goal: Low rate of false negatives
- TP / (TP + FN) x 100
What is sensitivity tests good for?
SNOUT
- NEGATIVE result is good for ruling OUT
Define specificity. What does a high specificity indicate? Calc?
- identify negative results in patients who DO NOT have the disease
Goal: have low rate of false positives
TN / (TN + FP) x 100
What are specificity rests good for?
SPIN
- Positive result is good for ruling in
Define sensitivity of an assay
Range at which an assay can accurately measure an analyte
Define specificity of an assay
Degree of cross-reactivity of the analyte with other substances
What does a positive predictive value indicate?
What does a negative value indicate?
disease/no disease
+ predictive value = % of positive tests that are actually + (PRESENCE OF DISEASE)
- predicative value = % of negative tests that are actually - (ABSENCE OF DISEASE)
Which values are dependant on prevalence of disease? which values are not
Dependent = predictive value
Not dependent = Sensitivity, Specificity
Define reference range
A set of previously defined values for some measurement used to interpret a lab test result
What is gaussian normal distribution indicate about reference range and SD
- reference range can be 2 SD above/below the mean value
What effect does increasing reference range have on sensitivity?
Decrease sensitivity
Differentiate between quantitative and qualitative tests
Quantitative:
- Exact numerical measurement as an output
Qualitative:
- report an outcome as positive or negative without indication of the degree of positivity or negativity
What factors should you consider in age?
Children: physiological immaturity (predictable)
Elderly: physiological changes (less predictable)
What factors should you consider in pregnancy?
Troponin used to screen for blood clots
(it is increased during pregnancy, not accurate way to measure)
What does hemoconcentration vs hemodilution mean
hemoconcentration: little fluid
hemodilution: fluid overload
Explain methodological interference
drug interferes with analyte of interest
Explain drug induced organ damage
drug can induce renal dysfunction
Explain direct pharmacological effects
antibiotics inhibit bacterial growth in urine/blood
What is the practical framework for interpretation and management of abnormal values (6)
- How abnormal is the lab value compared to reference range
- farther away = abnormal - Consider patient specific factors
- some factors can explain abnormal values
- some tests have different ranges for different factors (age, gender) - asses value to baseline value (assess rate of change)
- Faster rate of change = clinical risk
- intrapatient changes is expected? - assess value to baseline value (see potential trends)
- continued trend up or down may be clinically important
- small fluctuations are expected - Is the abnormality clinical significant
- Does it require management
