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Laboratory Operations
31 cards from 2 lessons in Laboratory Operations, each linking to the passage it came from.
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Quality Control, Method Evaluation, and Quality Management
How is the arithmetic mean of control results calculated?
Add the results and divide by their count.
Read the passage: Statistical control of a measurement procedure
What does standard deviation describe, and in which units?
The spread of results around the mean, in the original measurement units.
Taking the square root of variance restores the analyte's units.
Read the passage: Statistical control of a measurement procedure
How are variance and standard deviation related?
Variance = SD².
Variance therefore has squared measurement units.
Read the passage: Statistical control of a measurement procedure
What is the formula for coefficient of variation?
CV (%) = SD ÷ mean × 100.
Dividing by the mean lets imprecision be compared across control levels and methods.
Read the passage: Statistical control of a measurement procedure
For a Gaussian distribution, about what percentage lies within ±1 SD of the mean?
For a Gaussian distribution, about what percentage lies within ±2 SD of the mean?
95.4%.
About 4.6% lies outside these limits in total.
Read the passage: Statistical control of a measurement procedure
For a Gaussian distribution, about what percentage lies within ±3 SD of the mean?
99.7%.
About 0.3% lies outside these limits in total.
Read the passage: Statistical control of a measurement procedure
If an interval is defined as mean ±2 SD, how many SD wide is it?
Four SD.
It extends two SD in each direction from the mean.
Read the passage: Statistical control of a measurement procedure
What appears on the two axes of a Levey-Jennings chart?
The vertical axis carries the control result, and the horizontal axis carries time or run number.
Horizontal lines at the mean and SD limits show how far each result falls from the mean.
What control-chart pattern is called a shift?
An abrupt move to a new level that persists on one side of the earlier level.
It suggests systematic error.
What control-chart pattern is called a trend?
Progressive movement in one direction.
The laboratory's adopted rule sets how many consecutive results moving in one direction count as a trend.
What pattern does random error add to repeated control measurements?
Unpredictable scatter.
Individual deviations vary in direction and size.
What triggers 1₂s when the rule is used as a warning?
One control result beyond either 2 SD limit.
It prompts a check of the control results against the laboratory's rejection rules.
What triggers the 1₃s rejection rule?
One control result beyond either 3 SD limit.
A large isolated deviation meets this rule.
What triggers 2₂s?
Two consecutive results beyond the same 2 SD limit.
Both must deviate in the same direction.
What triggers R₄s?
Within one run, one result above +2 SD and another below −2 SD.
Their separation exceeds 4 SD.
What triggers 4₁s in simultaneous multirule use?
Four consecutive results beyond the same 1 SD limit.
All four lie on the same side of the mean.
What triggers the selected 10x sequence rule?
Ten consecutive control results on one side of the mean.
Each result can still lie inside ±2 SD.
In simultaneous multirule use, does a result within ±2 SD bypass sequence rules?
No. Check the results against every rule the laboratory uses.
A sequence can meet a rejection rule without an isolated 2 SD warning.
Do you interpret R₄s within a single run or across runs?
Within a single run.
Pairing deviations from different runs mixes a between-run shift into a rule meant to catch random error within one run.
What is the sigma-metric formula when all inputs are percentages?
Sigma = (allowable total error % − |bias %|) ÷ CV %.
A different allowable error goal, or bias and CV measured at another concentration, gives a different sigma.
Why does the sigma calculation use the magnitude of bias?
Bias in either direction uses part of the allowable error.
Subtracting a signed negative bias would incorrectly increase the remaining allowance.
With bias defined as candidate minus comparator, what does a positive bias mean?
The candidate method gives higher results on average.
State the subtraction direction when reporting bias.
Why is a high correlation coefficient not enough to show that two methods agree?
Results can track closely and still differ systematically.
Measure the bias between the methods at the concentrations where patient results fall.
Laboratory Mathematics and Diagnostic Performance
How is the specimen fraction of a dilution calculated?
Specimen volume ÷ final volume.
This fraction tells you how much of the finished mixture came from the original specimen.
Which quantities are needed to calculate molarity?
Moles of solute and the final solution volume in liters, because molarity = mol ÷ L.
The final solution volume includes the dissolved solute.
How do you convert solute mass in grams to moles?
Moles = mass in g ÷ molar mass in g/mol.
The gram units cancel, leaving mol.
What formula gives the mass needed for a solution at a specified molarity and final volume?
Mass = mol/L × final volume in L × molar mass in g/mol.
The other units cancel, leaving grams of solute.
How do you rearrange C₁V₁ = C₂V₂ to find the stock volume V₁?
V₁ = C₂V₂ ÷ C₁.
C₁ and C₂ need matching concentration units. The calculated V₁ has the same volume unit as V₂.
How do you convert a mass concentration from mg/dL to mg/L?
How do you convert mg/L to mmol/L using molar mass in mg/mmol?
mmol/L = mg/L ÷ molar mass in mg/mmol.
The mass units cancel. Use the molar mass of the stated measurand.
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