Lab Math Exam

High diagnostic sensitivity

What is the most desirable form of screening test due to minimal false negatives

Increase specificity and decrease sensitivity

What does raising a cutoff value do in a screening test

Two consecutive controls greater than ± 2 SD

What starts the cause for rejecting an analytical run

Analyte concentrations that reflect the analytic measurement range and match patient samples

What makes a good QC material

Delta check

Used to investigate differences between two results from the same patient on the same day to catch preanalytical errors

Colligative properties

Freezing point depression, boiling point elevation, vapor pressure depression, osmotic pressure that depend on the number of dissolved particles

Precision

Reproducibility evaluated with CV and F-test

Accuracy

Closeness to the true value evaluated by t-test

Sensitivity/screening

Ability to detect disease and minimize false negatives

Specificity/confirmation

Ability to identify absence of disease and minimize false positives

Positive prediction value

Probability that a positive test means you actually have the disease

Negative predictive value

Probability that a negative test means you actually do not have the disease

Transfer/verify a reference interval

Requires 20 healthy patients and passes if 10% or less fall outside of the range.

Obtain 20 additional samples and pass if two or less fall outside the range

What to do if RI verification fails

Establish a new reference interval

Requires 120 healthy patients using 2.5th-97.5th percentiles due to natural skew

Proficiency testing

Blind external validation tested like patient samples to compare analyzers twice a year

All proficiency testing failures must be resolved in 30 days

What is the rule of PT

1_2s warning

One point outside ± 2SD

1_3s reject

1 point outside 3± SD to indicate random error

2_2s reject

2 consecutive points outside the same ± 2SD limit to indicate systematic error

R_4s reject

Range between consecutive runs exceeds 4 SD to indicate random error

4_1s reject

4 consecutive points exceed the same ± 1 SD to indicate systematic error

10_x reject

10 consecutive points fall on the same side of the Mean to indicate systematic error

Trend

Gradual deviation in one direction for 6 runs

Shift

Abrupt change establishing a new pattern for 6 runs

Analysis of control serum over 20 days

How to prepare a new Levey-Jennings chart

Constant error

Shift stays the same regardless of concentration (inference studies)

Proportional error

Shift gets worse as concentration increases (recovery studies)

Hemolysis

Intracellular components of burst RBCs leak into serum

Icterus

Caused by high bilirubin

Lipemia

Caused by high triglycerides and fats in the blood sample

Ammonia and Arterial Blood Gas

What types of analytes need to be kept on ice

Serum

No anticoagulant and is allowed to clot due to the lack of fibrinogen

Plasma

Contains anticoagulant and fibrinogen, and WBCs, platelets, and RBCs when spun

Arterial blood

Blood drawn from the radial artery

High K+ and low Ca2+

What signs suggest EDTA contamination

Diluted analytes with sugar and electrolyte spike

What signs suggest IV fluid contamination

Chlorhexidine

What should you use instead of alcohol wipes for Blood Alcohol tests

Fist pumping

What causes falsely elevated potassium and lactic acid levels

Prolonged tourniquet

What causes hemoconcentration and elevated analyte levels

Light

What must bilirubin be protected from

Beer’s law

Absorbance is directly proportional to concentration

Transmittance has a logarithmic inverse relationship to concentration

Absorbance and Transmitting relationship

Stock volume/Total volume

Dilution fraction

Normality

One gram equivalent weight of solute per liter of solution

Molarity

Moles of solute per 1 L of solution