QUALITY CONTROL

quality control

• involves the systematic monitoring of analytic processes to detect analytic errors that occur during analysis and to ultimately prevent the reporting of incorrect patients test results

sensitivity

• it is the ability of an analytical method to measure the smallest concentration of the analyte of interest

specificity

• it us the ability of an analytical method to measure only the analyte of interest

accuracy

• the nearness or closeness of the assayed value to the true or target value

precision or reproducibility

• the ability of an analytical method to give repeated results on the same samples that agree with on another

reliability

• the ability of an analytical method to maintain accuracy and precision on the extended period of time

diagnostic sensitivity

• it is the ability to detect the proportion of individuals with the disease who test positively with the test

diagnostic specificity

• it is the ability of the test to detect the proportion of individuals without the disease who test negatively for the disease

intralab (internal quality control)

• involves the analyses of control samples together with the patient specimen. it detects changes in the performance between the present operation and the stable operation

• it is important for the daily monitoring accuracy and precision of analytical method

• detects both random and systematic error

interlab (external quality control)

• it involves proficiency testing programs that periodically provide samples of unknown concentration of analytes to participating laboratories

• it is important in maintaining long-term accuracy of the analytical methods

pooled sera (in-house qc material)

• left over sera

• froze for 72 hours at -20 deg celsius, then allowed to thaw at 6 deg celsius for 16 hours

lyophilized form (solid-powder form)

• commercial quality control material

• 2-8 deg celsius, freezing (best storage), shelf life is 24 hrs

non-lyophilized form

• liquid form

random error

• in determining error or imprecision

• it is the basis of varying differences between repeated measurements, it is due to instrument, operator and environmental conditions

• variations techniques: pipetting error, mislabeling of samples, temperature fluctuations, improper mixing of sample and reagents

systematic error

• inaccuracy

• it is an error that influences observations consistently in one direction, it detects positive and negative bias, often related to calibration problem, inadequate reagent blanks. leaky ise, failing instrumentation and poorly written procedure

clerical error

• the highest frequency of clerical errors occurs with the use of a handwritten labels and request forms

statistics

• it is the science of gathering, analyzing, interpreting and presenting data

mean

• a measure of central tendency, it is associated with symmetrical or normal distribution, it measures accuracy or system error

standard deviation

• a measure of the dispersion of values from the mean, it helps describe the normal curve, it measures prevision or random error

coefficient of variation

• a percentile of the mean and index of precision and depression

variance

• it is called standard deviation squared, a measure of variability

t-test

• it is used to determine whether there is a statistical significant difference between the means of two groups of data

f-test

• it is used to determine whether there is statistically significant difference between the standard deviations of two groups of data

quality control chart

• graphically represent the observed values of a control material over time in the context of the upper and lower control limits in relation to the target value

gaussian curve

• it is used to visualized accuracy and precision

• it occurs when the data set can be accurately described by the standard deviation and the mean, it focuses on the distribution of errors from the analytical method rather than the value from a healthy or patient population

cumulative sum graph

• it calculates the differences between quality control results and the target means, the most common method is the v-mask which requires computer implementation

• it identifies consistent bias problems

youden/twin plot

• it is used to compare results obtained on a high and low control serum from different laboratories

shewhart levey-jennings chart

• most widely used quality control chart in the clinical laboratory

• it allows the laboratories to apply multiple rules without the aid of a computer

trend

• it is a gradual lost of reliability, formed by control values that either increase or decrease for six consecutive days

• main cause: deterioration of reagent

shift

• it is formed by control values that distribute themselves on one side or either side of the mean for six consecutive days

• main cause: improper calibration of the instrumet

outliers

• these are control values that are far from the main set of values

• main cause: random or systematic errors

westgard control rules

• It recognizes the use of simple upper and lower limits that are not enough to identify analytical problems