Quality Control (Clinical Chemistry) Flashcards
References: CC ni Hyacinth Yambao CC ni Rovie Vila
3 parts of Pre-analytical phase
- Patient Identification
- Patient Preparation
- Phlebotomy
The process of verifying a patient’s identity, is the most important step in specimen collection.
Patient identification
Why patient identification is the most crucial part of pre analytical phase?
Patient identification is defined as the process of verifying a patient’s identity and is also considered as the most crucial step of specimen collection. It is necessary in the laboratory testing process due to the fact that misidentifying a patient specimen or collecting specimen from the wrong patient can lead to fatal and detrimental repercussions.
Furthermore, if proper patient identification is not followed religiously the results that the laboratory will release cannot be reliable for the proper diagnosis of the patient and this can result and misdiagnosis of disease and the conduct of improper treatment leading to substandard and poor patient outcomes
Guidelines that (Accuracy in Patient and
Sample Identification) recommends having the patient spell the last name.
CLSI guideline GP33-A
What is the minimum identifier?
- 2
- name and birthdate
Hormone that is being collected while the patient is sleeping
Cortisol
3-Way IDENTIFICATION
1) patient’s verbal ID statement,
2) check of the ID band,
3) visual comparison of the labeled
specimen with the patient’s ID band
before leaving the bedside.
it is a part of the process management component of the quality system that integrates good laboratory practices to ensure correct patient results
Quality control
it is the process of ensuring that analytical results are correct by testing known samples that resemble patient’s sample and comparing their determined values with their expected values
(control values)
Quality Control
it is the process of ensuring that analytical results are correct by testing known samples that resemble patient’s sample and comparing their determined values with their expected values
(control values)
Quality Control
What are objectives of Quality control?
• To check the stability of the machine
• To check the quality of reagents
• To check technical errors (personnel)
process of verification by comparing the accuracy of the measuring instrument against a reference standard
Calibration
• This are substances with known concentration used
• It is done every 6 months or more frequently if recommended
by the manufacturers
Reference Standard
2 types of reference standard
o Primary Standard
o Secondary Standard
Is an ultra-high purity grade compound used in analysis involving assay, identification or purity tests
- Reference material
Primary standard
These are also high purity grade materials which are quantified in relation to primary standards and put to routine use in laboratories.
- most commonly used in the lab
Secondary standards
Characteristic of an ideal QC materials
• It should resemble human sample
• Inexpensive and stable for long periods
• No communicable diseases
• No matrix effects/known matrix effects
• With known analyte concentrations
• Convenient packaging for easy dispensing and storage
2 Types of quality control
- INTERNAL QUALITY CONTROL (Intralaboratory Quality control)
- EXTERNAL QUALITY CONTROL (Interlaboratory Quality control)
• Analyses of control samples together with the patient specimens
• Daily monitoring of accuracy & precision of analytical methods.
• Detection : Random and Systematic error
INTERNAL QUALITY CONTROL (Intralaboratory Quality control)
• It involves the proficiency testing programs that periodically provide samples of unknown concentrations to participate in clinical laboratories
• It is important in maintaining long-term accuracy of the analytical methods
EXTERNAL QUALITY CONTROL (Interlaboratory Quality control)
What is the gold standard for clinical laboratory external QC testing?
College of American Pathologists Proficiency program
2-level os control solutions
Clinical Chemistry
3-Level Control Solutions
Immunology
It is the nearness or closeness of the assayed value to the true or target value
Accuracy
accuracy is estimated using three different types of studies:
- Recovery
- Interference Studies
- Patient Sample Comparison
degree by which a method is easily repeated
Practicability
ability of the method to maintain accuracy and precision over a period of time
Reliability
(Imprecision; Indeterminate)
affect the precision of the test system (e.g., pipetting technique)
- Human error
- not preventable
Random error
(Inaccuracy/ Determinate)
affect the accuracy of the test system
- Preventable
- there is trend
Systematic error
a sudden upward or downward change that lasts for four or more consecutive values (e.g., equipment malfunction, instrument adjustments)
Shift
tendency of results to gradually increase or decrease over a period of time (e.g., contamination, reagent deterioration gradual equipment failure)
Trend
Values: far from the main set of values
Highly deviating values
Random or systematic errors
Outliers
Degree of flatness or sharpness
Kurtosis
National reference lab for Clin chem
Lung Center of the Philippines
National reference lab for Toxicology
East Avenue Medical Center
What is the most common laboratory tests performed in the external quality control or in clinical chemistry?
- FBS (Glucose)
- BUN
- Uric acid
- Creatinine
- Cholesterol
- Triglyceride
- Total protein
- Albumin
- Sodium
used to observe values of control materials overtime to determine and detect errors such as inaccuracy and imprecision.
QC charts
• This plot will give the earliest indication of systematic errors (trend) and can be used with 13s rule.
• Very sensitive to small, persistent errors that commonly occur in the modern, low-calibration frequency analyzer
Cumulative sum (CUSUM)
It is used to compare results obtained on a high and low control serum from different laboratories
Youden/twinplot
• Dot chart
• Most widely used system in clinical laboratory
• Allows the laboratorians to apply multiple rules without the aid of a computer
• Easy identification of random and systematic errors.
Shewhart-levey jenings chart
• Present in all measurement; due to chance
• Basis for varying differences between repeated measurements
• Due to instrument, operator &
environmental conditions.
Random error
• Is an error that influence
observations consistently in one
direction
• Detected either positive or negative bias.
Systemic error
What are the random errors?
• Pipetting errors
• Mislabeling of samples
• Temperature and Voltage fluctuation
• Improper mixing of samples & reagent
• Dirty optics
What are the systematic errors?
• Calibration problem
• Deterioration of reagents & control
• Unstable and inadequate reagent blanks
• Contaminated solutions
• Failing instrumentation
• Poorly written procedures
• Incorrect sample & reagent volume
A pair of medical decision points that span the limits of results expected for a defined healthy population
Reference Interval
What are the applications of reference intervals that can be grouped into three
main categories?
- diagnosis of a disease or condition
- monitoring of a physiologic condition
- monitoring therapeutic drugs
Range of values that include a specified probability, usually 90% or 95%
- we are using the 95% (±2SD)
Confidence Interval
defines the interval by the mean ±1.96 SDs
= 𝑥 ±1.96 SD
Parametric Method
the reference interval is determined by
using the central 95% of values; the
reference range is therefore defined by
the 2.5th to the 97.5th percentiles
- usual/most commonly used
Non-Parametric Method
is the ability of the analytical method to measure the smallest concentration of the analyte of interest
• screening test
Analytical Sensitivity
is the ability of an analytical method to measure only the analyte of interest
- Confirmatory test
Analytical Specificity
- ability of a test to detect a given disease or condition
- proportion of individuals with that disease who test positively with the test
Diagnostic Sensitivity
- ability of a test to correctly identify the absence of a given disease or condition
- proportion of individuals without a condition who have a negative test for that condition
Diagnostic Specificity
the predictive value of a positive test refers to the probability of an individual having the disease if the result is abnormal (“positive” for the condition)
Positive Predictive Value
refers to the probability that a patient does not have a disease if a result is within the reference range (test is negative for the disease)
Negative Predictive Value
±1𝑆𝐷 =
68.3% 𝑜𝑓 𝑜𝑏𝑠𝑒𝑟𝑣𝑎𝑡𝑖𝑜𝑛s
±2𝑆𝐷 =
95.4% 𝑜𝑓 observations
±3𝑆𝐷 =
99.7% 𝑜𝑓 𝑜𝑏𝑠𝑒𝑟𝑣𝑎𝑡𝑖𝑜𝑛𝑠
- Used as a rejection or warning rule when one control result exceeds the mean +/- 2SD
- FOR SCREENING PURPOSE.
- Considered as a warning rule, but if the company consider it as a rejection rule, it should be a rejection rule.
- Random error
12S rule
• If 1 control observation exceeds 𝑥 ± 3s limit
• REJECT THE RUN FOR PROBABLE.
• Random Error
13s rule
• If 2 consecutive control values are greater than 𝑥 ± 2s
limit
• REJECT THE RUN FOR PROBABLE
• Systematic Error.
22s
• If the difference between the 2 controls is equal to or greater than 4s.
• REJECT THE RUN FOR PROBABLE.
• Random Error.
R4s
• If 10 consecutive control values falls on one side of the mean.
• REJECT THE RUN FOR PROBABLE.
• Systematic errors
10x
- If 4 consecutive control values are greater than 𝑥 ± 1s limit
- REJECT THE RUN FOR PROBABLE
- Systematic Error.
41s
