CC1 PART 1

*No formulas and Units

SI Unit/Metric System Conversions

Move the decimal point by the difference between the exponents either to the right (larger to smaller unit) or to the left (smaller to larger unit) of the number given.

Molarity

number of moles of solute per liter of solution

Molality

number of moles of solute per kilogram solvent

Normality

number of equivalent weights of solute per liter of solution

Equivalent weight

If the solute is expressed in terms of g/dL, multiply it by 10 to convert it into Liters then divide it by the ?

Percent solution

amount of solute per 100 total units of solution; expressed as % w/v, w/w, or v/v

Dilution

done when the analyte concentration is too high and exceeds the detection limit of the method; expression of relative concentration

Dilution of stock solution

done when a weaker reagent concentration is needed than the stock substance available

Ratio

amount of something relative to another; expressed as part per part or part per whole

Valence

the number of hydrogen atoms, hydroxyl, OH units, or the number of electron loss or gain.

1. Mean (x̄)

2. Median

3. Mode

What are the Measures of Center?

• Central Tendency

Mean

average or arithmetic mean

• In laboratory statistics, mean is commonly used

• corresponds to the center in the Levey-Jennings chart or to the center of the gaussian curve.

Median

midpoint of a data set after the values have been rank-ordered

Mode

most frequently occurring value in a data set

1. Standard Deviation

2. Coefficient of Variation

3. Range

What are the Measures of Spread?

• Distribution / Variability

Standard Deviation(s)

distribution of data points around the mean; primary measure of uncertainty

Variance (s²)

Summation of the squares of the differences between the mean and its observation divided by the total number of observations minus one degree of freedom

Coefficient of Variation

best indicator of Precision

• Expressed in terms of percent (%)

Range

difference between the highest and lowest values in a data set

• This is the most unreliable when there are outliers.

Inversely related

Relationship between CV and Precision

Rule of thumb

in general or for most methods: the CV must be less then 10%.

Outliers (1)

values the deviate greatly from the mean

• If there is a value that is too far from the mean, that will make the range value a large number, that would not present the distribution for most values.

Gaussian / Normal Distribution

• Data points are distributed symmetrically around the mean (bell-shaped curve) with most values close to the center.

• Mean, Median and Mode are identical

• Follows the empirical rule

Empirical Rule

• A data set that displays a normal distribution follows the so-called ___________

• If the values are plotted in a graph, and the data set displays normal distribution, 68% of the values will fall in +/- 1 standard deviation. 95% are approximately would fall within +/- 2 standard deviation. And approximately 99.7% of the values would fall within +/- 3 standard deviation

68, 95, 99.7%

The Empirical Rule is:

95% interval

The most commonly used confidence interval is

1. Reference interval

2. Verifying a reference interval

3. Establishing a reference interval

What are Interval Studies?

Reference Interval

pair of medical decision points that span the limits of results expected for a defined healthy population

Verifying a reference interval

• done to confirm the validity of an existing or published RI for an analyte

• requires at least 20 study individuals; RI is adopted if ≤10 of the subjects fall outside the range

Establishing a reference interval

• done when there is no existing RI for an analyte or when transference studies fail

• requires at least 120 study individuals; RI is set based on the %Cl = x̄ ± 2s

1. Precision study

2. Recovery study

3. Inferential statistics

4. Analytical sensitivity

5. Analytical specificity

6. Diagnostic Efficiency / Accuracy

What are some Method Evaluation?

Precision study

• first step in method evaluation; usually done by running two control materials twice a day over a 10-day period

  • also known as 2×2×10 scheme

Recovery study

• involves spiking a sample with a known amount of an analyte and determining how much of it can be detected by the method in the presence of other compounds in the matrix

T test

UNDER INFERENTIAL STATISTICS:

Compares the means of two groups of data or the accuracy of the two methods

F test

UNDER INFERENTIAL STATISTICS:

• Compares the standard deviation of two groups of data or the precision of two methods.

Linear Regression

UNDER INFERENTIAL STATISTICS:

• used in comparison-of-methods test and bias studies

• quantitative variables

x axis

UNDER LINEAR REGRESSION:

• Independent variable; reference method

• also shows as Reference Method

• AXIS

  • Abcyssa, X axis, Independent variable, Std / Ref. Method

y axis

UNDER LINEAR REGRESSION:

• Dependent variable; test/New method

• also shows as Test Method

Slope

UNDER LINEAR REGRESSION:

• Change represents Proportional Error

y - intercept

UNDER LINEAR REGRESSION:

• Change represents Constant Error

Correlation coefficient (r)

UNDER LINEAR REGRESSION:

Represents the strength of the relationship between the two methods

Analytical sensitivity

• ability of a method to detect the smallest concentration of an analyte

• Not prone to false negative; desired in screening test

Analytical specificity

• ability of a method to detect only the analyte of interest

• Not prone to false positive; desired in confirmatory test

Diagnostic Sensitivity

UNDER DIAGNOSTIC EFFICIENCY:

• ability of a test to detect a given disease or condition; proportion of individuals with the disease who have a positive test result; desired for conditions that are severe or require immediate treatment

Diagnostic Specificity

UNDER DIAGNOSTIC EFFICIENCY:

• ability of a test to detect the absence of a given disease or condition; proportion of individuals with no disease who have a negative test result; desired when the consequences of a false positive result are severe

Positive predictive value

UNDER DIAGNOSTIC EFFICIENCY:

• probability that a positive test result indicates disease; proportion of individuals with a positive result who truly have the disease

Negative predictive value

UNDER DIAGNOSTIC EFFICIENCY:

• probability that a negative test result indicates absence of disease; proportion of individuals with a negative result who truly do not have the disease

Pre-analytical 1

UNDER QUALITY ASSESSMENT / QUALITY ASSURANCE:

• All steps done PRIOR to sample analysis

• include test requisition, patient preparation, patient identification, specimen collection, labeling, specimen transport, specimen reception, handling, and preparation

Analytical 1

UNDER QUALITY ASSESSMENT / QUALITY ASSURANCE:

• include reagents, preventive maintenance of equipment, calibration, analysis of samples, and quality control

Quality Control

Special aspect of analytical testing or laboratory testing

Post-analytical 1

UNDER QUALITY ASSESSMENT / QUALITY ASSURANCE:

• include verification of calculations and reference ranges, flagging and notification of panic/critical values, delta checks, reporting of results, and interpretation

Delta Check

• Means “change”

• an algorithm in which a current laboratory result is compared with results obtained on a previous specimen from the same patient

• Check if the current result or change in trend agrees with the previous result of the same patient

Pre-analytical 2

These are examples from what errors?

Analytical 2

These are examples from what errors?

Post-analytical 2

These are examples from what errors?

Reliability

UNDER QUALITY CONTROL:

• ability to maintain accuracy and precision over an extended period of time during which equipment, reagents, and personnel may change

• ACCURACY + PRECISION

Accuracy

UNDER QUALITYCONTROL:

• closeness of the result to the true or actual value

Precision

UNDER QUALITYCONTROL:

• ability to produce a series of results that agree closely with each other; expressed in terms of CV; also called repeatability / reproducibility

Repeatability

• using the same condition; within run position.

• The test is repeated with same machine, same patient, same personnel that resulted with same result

Reproducibility

• between run position or inter lab; under changed condition.

• Test are repeated with different laboratory, different machine, different reagent, and different medtech but resulted with the same result

• Important in External Qc

Internal Quality Control

UNDER QUALITY CONTROL:

• Involves the analysis of at least 2 levels of control every 24 hours

• Initial control limits are established for at least 20 consecutive days

• Important for the daily monitoring of accuracy and precision

1 Normal Control and 1 Pathologic Control

The two levels for Internal QC are:

External Quality Assessment

UNDER QUALITY CONTROL:

• Involves testing blind samples (unknown concentration of analytes) sent periodically by regulatory agencies to participating laboratories

• Important for maintaining long-term accuracy of analytical methods

• SDI = (Lab result - Group Mean) / Group SD

• Results must be 2 standard deviations away from the mean using a 95% confidence interval

• SDI >2 indicates poor performance. It means that laboratory results are outside the confidence interval. It does not agree with other participating laboratory.

National External Quality Assessment Scheme (NEQAS)

is the regulatory agency administered by National Representatives (NRs)

Lung Center of The Philippines

In our country the national reference laboratory for clinical chemistry or biochemistry is the

Neither accurate nor precise

This is a representation of:

Precise but not accurate

This is a representation of:

Accurate but not precise

This is a representation of:

Both accurate and precise

This is a representation of:

Random Error

UNDER ANALYTICAL VARIATION (TYPES OF ERROR IN LAB TESTING):

“Imprecision“

• Due to chance or an unpredictable cause; does not recur in regular pattern

• Affects precision; indicated by violation of the 12s, 13s, R4s Westgard rules

• Causes: instrument instability e.g. temperature and voltage fluctuations, dirty glassware, sampling error, improper mixing of sample and reagent, operator variability e.g. pipetting error, anticoagulant or drug interference

Systematic Error

UNDER ANALYTICAL VARIATION (TYPES OF ERROR IN LAB TESTING):

“Inaccuracy / Bias”

• Recurring error inherent in test procedure; influences observations in one direction

• Affects all results; may be constant or proportional

• Affects accuracy; indicated by shift, trend, or violation of the 22s, 41s, 81s, and 10x Westgard rules

• Causes: deterioration of reagents, change in reagent lot, unstable reagent blanks, calibration error, changes in standard concentration, contaminated control solutions, diminishing lamp power, dirty photometer, faulty ISE, and pipettor maintenance error

Shift

UNDER ANALYTICAL VARIATION (PATTERNS IN QC CHARTS THAT INDICATE ERRORS):

• abrupt change in the distribution of control values such that they accumulation one side of the mean for 6consecutive days; major cause calibration error / error in standard prep.

calibration error / error in standard prep.

What is the major cause of Shift?

Upward shift

If the standard is diluted or prepared at a lower concentration, the result will be higher than expected (falsely high/increased).

Downward shift

If the standard is prepared at a higher concentration, the result will be lower than expected (falsely low).

Trend

UNDER ANALYTICAL VARIATION (PATTERNS IN QC CHARTS THAT INDICATE ERRORS):

• gradual change in the distribution of control values such that they continue to increase or decrease over a period of 6 consecutive days passing through the mean; major cause deterioration of reagents.

deterioration of reagents.

What is the major cause of Trend?

Outliers (2)

UNDER ANALYTICAL VARIATION (PATTERNS IN QC CHARTS THAT INDICATE ERRORS):

• highly deviating control values caused by random or systematic errors.

Systematic Error 2

Shift and Trend are examples of what error? Systematic or Random?

Shewhart Levey-Jennings chart (LJ Chart)

UNDER ANALYTICAL VARIATION (INTERPRETATION OF QUALITY CONTROL RESULTS):

• most commonly used QC chart

1_2s

WESTGARD CONTROL RULES:

• One control value exceeds either ±2 SDs from the mean. Warning rule; initiates testing of other rules

ERROR DETECTED:

• Used as a warning rule Prompt testing of other control rules

• Detects imprecision but still acceptable

DECISION:

• ACCEPT

1_3s

WESTGARD CONTROL RULES:

• One control value exceeds either ±3 SDs from the mean.

  
  

ERROR DETECTED:

• Detects imprecision or systematic bias

DECISION:

• REJECT

R_4s

WESTGARD CONTROL RULES:

• Range between two levels of control within a run exceeds 4SDs

ERROR DETECTED:

• Detects imprecision

DECISION:

• REJECT

2_2s

WESTGARD CONTROL RULES:

• Two consecutive values or values for two QC samples exceed 2 SDs from the meaning the same direction

ERROR DETECTED:

• Bias Inaccuracy

DECISION:

• REJECT

4_1s

WESTGARD CONTROL RULES:

• Four consecutive control values exceed 1SD from the mean.

  
  

ERROR DETECTED:

• Bias Trend

DECISION:

• REJECT

10x̄ (8/12x̄)

WESTGARD CONTROL RULES:

• Ten(eight or twelve)consecutive control values are on the same side of the mean

  
  

ERROR DETECTED:

• Bias Trend

DECISION:

• REJECT

12s, 13s, and R4s

These are Westgard Control Rules that are random errors which indicates imprecision

22s, 41s, 81s, and 10x̄

These are Westgard Control Rules that are systematic errors which indicates inaccuracy

1_2S Rule

Illustration of what rule?

• 1 control value is above or below the +/-2S

1_3S Rule

Illustration of what rule?

• 1 control value is above or below the +/- 3S

R_4S Rule

Illustration of what rule?

• The range is 4 SD (+/-2S) away from each other.

• Always within a run that involves 2 levels of control.

• Do not confuse with 22S

  • R4S is a one-time error.

2_2S across runs

Illustration of what rule?

• A single level of control

• Two consecutive days violation of 1_2S

2_2S across controls

Illustration of what rule?

4_1S across runs

Illustration of what rule?

4_1S across controls

Illustration of what rule?

10_X across runs

Illustration of what rule?

10_X across controls

Illustration of what rule?

Serum

Preferred sample for most clinical chemistry tests

1000-2000g (RCF)

10 mins.

Preparation for Serum and Plasma:

• Liquid portion of clotted or anticoagulated blood prepared by centrifugation at ____________ for __________

glucose, K, PO4, HCO3, Albumin, CK, AST

Serum value > Plasma value: __________________