Chem: Section 2- QA and QC

a process that includes a set of activities that aids in improving the reliability of the laboratory as a whole

quality assessment/assurance/management

a solution or chemical substance of known concentration that mimics a patient's specimen; has the same matrix as patient samples

quality control

closeness to the true value (correctness)

accuracy

the ability of a lab result to be repeated (reproductibility)

precision

mathematical average

mean

value that occurs the most frequently in a group of data points

mode

middle number in a group of data points

median

describes the distribution of all values around the mean for a particular group

standard deviation

a number that describes the number of standard deviations away from the mean that a result is (2% is ideal)

SDI

used to compare the standard deviations of two samples; can be used to compare test results within the same lab, or with the same test from another lab (10% is ideal)

CV

a sudden and sustained change in quality control results above or below the mean, that continues at the same level

shift

a gradual but steady change in quality control results, moving up or down away from the mean

trend

the range of values for a given analyte in a defined population, derived from a group of "normal and healthy" individuals

reference range

difference, observed result minus the assigned value

bias

when accuracy and precision are met

reliability

error of a procedure

variance

an error that occurs unpredictably due to poor precision; ID'd by a sudden fluctuation in the QC measurement, in either direction

random error

List some examples of a random error.

reagent dispensing, sample evaporation, temp of analyzer, optical system, environmental conditions, calibrator reconstitution, instability of instrument, variation in specimen handling techniques, variation in operators

a recurring error that affects all results, can be ID'd by a trend in QC measurement

systematic error

List some examples of a systematic error.

aging reagents or calibrators, instrument components, optical changes, fluctuations in voltage, wear and tear of instruments, reagent lot variability, calibration differences, technologist interactions

occurs when you reject a control when it should be accepted

type I QC error

occurs when you accept a control when it should be rejected

type II QC error (worse than type I because it does affect patient results)

the connection or correlation with results and patient S/S, disease, etc.

relevancy

the ability to detect small concentrations of the measured analyte

analytical and diagnostic sensitivity

freedom from interference and cross reactivity to determine solely the analyte that is being measured

analytical and diagnostic specificity

the amount of error that can be tolerated without invalidating the medical usefulness of the analytical result

allowable error

the range of a specimen concentration that can be accurately measured by a test method

Linearity/reportable range/analytical measurement range (AMR)

the fraction of positive/negative test results that are true positives/negatives

Positive and negative predictive values

checking the lab's performance by using an external agency or facility

External quality assurance program

everything that affects a patient specimen before it is tested for the analyte (complete physician's orders, codes, patient ID, patient compliance, collection, labeling, processing of specimen, storage, transport, contamination)

preanalytical

every step involved in the actual analysis of a laboratory specimen

analytical

What are some examples of analytical activities?

anything part of the test procedure- e.g. diluting, reagent prep, instrument maintenance and calibration, quality control, proficiency testing, production/printing of the lab report

the variables that affect patient results in the reporting stage (positively identifying the test report with the patient sample, TAT, understandable report format, delta checks, notification of results arriving from external facility, patient notification, disposal of specimen, disinfection/decontamination)

post-analytical

used to assess the validity of individual laboratory results as compared to a peer group, useful to see your lab's accuracy and precision

SDI

What is a good and bad SDI score?

0=perfect, greater than 2SD is cause for concern

describes the standard deviation relative to its mean, so that one may easily compare precision over the analytical range of the assay; useful for identifying sampling errors and procedural factors such as instrumentation or reagents

CV

the CV score represents the __________________ of a test

imprecision

A CV of less than _____% if acceptable

10% (15% for low level assays may be acceptable)

What are the 3 requirements for competency of lab personnel?

1. appropriate *education* for the task

2. *training* for the specific requirements of each test

3. *experience* in testing specific tests

How often must competency evaluations occur for lab personnel?

at hire, at 6mo, yearly

defines the requirements of every test in the lab

standard operating procedure (SOP)

What things does the SOP contain?

specimen requirements, handling and processing requirements, transportation requirements, test methodology, linearity, reference ranges, dilution info, interferences/limitations

evaluate individual test results on the basis of normal variation; computerized check that is performed to detect changes from earlier individual patient test results

delta checks

Delta checks are helpful to detect what?

misidentified specimens, results that are incompatible with life, clerical errors, or patients who are rapidly declining

Delta checks are a type of QA and are part a which analytical phase?

post-analytical

no additives (glass tubes have no clot activator, plastic tubes have clot activator)

red top

clot activator and gel serum separator, no anticoagulant

tiger top (red/gray SST)

may or may not have clot activator, has gel serum separator, no anticoagulant

gold top

sodium heparin, lithium heparin, or ammonia heparin inactivate thrombin, no gel

green top

sodium fluoride (antiglycolytic agent- preserves glucose up to 5 days by preventing RBCs from breaking down and using glucose) and potassium oxalate (anticoagulant), good for glucoses

light gray top

Sodium EDTA forms calcium salts, heavy metal analysis/trace element testing

dark blue top

What are some advantages and disadvantages of using a gel type collection tube for specimen collection?

Advantages: less manipulation of specimen, minimizes hemolysis over time, less chemical interaction of blood to serum, enhanced recovery of serum, decreased staff time (can pour over), lower frequency of error with testing, storage time

Disadvantages: chemical analytes in serum can start to absorb into gel over time and cause falsely lower result (TDM, RBC enzymes, lead, trace metals, hormones, renin, catecholamines)

Serum or plasma should be separated within ____ hours and tested within ____ hours.

separated within 2, tested within 4

What is the speed and time of blood centrifugation?

3000-3500 rpms for 10-15 minutes

What happens if you don't spin a blood tube long enough?

too little spinning leads to clots, yielding less serum

Why are first morning urines optimal?

analytes are most concentrated in the morning

What is the purpose of QC?

monitors the analytical aspects of a method, verifying that results from a given method are precise and accurate

What is the difference between assayed and unassayed controls?

assayed controls come with value ranges and unassayed controls do not come with ranges, you have to calculate them yourself

How is QC manufactured?

manufactured commercially from pooled serum

Per CLIA, QC must be performed a minimum of ___ samples at least _____ per day for each analyte

2 samples at least once per day per analyte

QC performed on internal samples (patient or control) to verify that all personnel are performing procedures using the same technical skills, and that results between techs are within acceptable ranges (comparison testing)

internal QC

built-in positive control that produces a colored band if working

Internal QC for qualitative testing

checks validity with an external manufactured positive and negative controls at intervals recommended by the manufacturer

external QC for qualitative testing

manufactured positive and negative controls that show as a range (e.g. urine dipstick colors)

external QC for semiquantitative testing

manufactured controls used to check the validity of lab test; two or three levels of control samples may be necessary to ensure that all levels are being accurately detected

external QC for quantitative testing

What are the 3 primary components that are evaluated in an IQCP program?

risk assessment, QC plan, quality assessment

What level of testing qualifies for IQCP programs?

nonwaived testing only

What is the difference between qualitative, semi-quantitative, and quantitative testing?

Qualitative: positive or negative, presence or absence

Semi-quantitative: range, urine dipstick

Quantitative: exact number for a result

What are the normal Gaussian distributions?

68% is within 1 SD

95% is within 2 SD

99.7% is within 3 SD

method for plotting and interpreting QC results to track random errors, shifts, or trends

Levey-Jennings charts

Verification of established ranges requires _____ data points

Verification of new ranges requires _____ data points

Verification of established ranges requires *20* data points

Verification of new ranges requires *120* data points

use a combination of decision criteria or control rules to decide whether an analytical run is "in control" or "out of control"

Westgard Rules

What are the actions that must be taken when QC fails?

1)rerun the QC sample ONCE and only once

2)follow the troubleshooting procedure in the SOP

3)service call

What are the 4 reasons for ordering a lab test?

Diagnosis, monitoring, screening, research

What is the process for establishing reference ranges?

sample "healthy" volunteers, usually associated with the laboratory. They complete a well-defined questionnaire that covers exclusion and identifiers partitioning data

cutoff values that help differentiate the presence of a particular disease from the absence of that disease

medical decision limits

positive result, pt has the disease

true-positive

positive result, pt does not have the disease

false-positive

negative result, pt does not have the disease

true-negative

negative result, pt has the disease

false-negative

What is the most affected test by hemolysis?

potassium

The mean is a good measure of accuracy or precision?

accuracy (and systemic error)

SDI and CV are good measures of accuracy or precision?

precision (and random error)

What type of error is a bias?

systematic error

What is the difference between defensive medicine and evidence-based practice?

Defensive medicine: covering all of your bases, "if..., then...".

Evidence-based practice: clinical decisions are founded on historical evidence of successful treatment, uses testing algorithms

an initial test that should detect everyone with the disease before they present with symptoms; should have high degree of sensitivity

screening test

a test used to verify the results of an initial test; should have a high degree of specificity

confirmatory test

testing that is used to diagnose disease should detect all positives without giving any false positives; should have a high sensitivity and high specificity

diagnostic testing

screening tests should have high ___________

confirmatory tests should have high ___________

diagnostic tests should have high _____________

screening: high sensitivity

confirmatory: high specificity

diagnostic: both

correlation of the new method with a comparison method; find the bias; performed in-house

comparison studies

samples are checked against analytical methods known to be free of interference; performed by manufacturer

interference studies

an indicator of the accuracy of a particular measurement- a measured amount of a known standard to patient specimen and tested against another patient specimen that does not contain the standard

recovery studies

What 3 studies are done during evaluation of a new method?

comparison, interference, and recovery studies

provide the best available approximation of a true value; have been established and reproduced across different measurement systems, labs, and over periods of time

Gold Standard Method