QA/QC

• over 400 analytes can be tested from a patients sample of blood, urin or saliva
• samples must be labelled correctly with the correct tube stating the time what sample and volume
• U & E = urea and electrolytes
• results can confirm diagnosis or aid differential diagnosis, monitor the progress of a disease or therapy and detect complications or side effects. they can also be used for screening purposes
• LFT = liver function tests
• some tests are specialized and only certain hospitals do them - more tests = increased quality
• patients history and narrative are very important for differential diagnosis
• point of care tests (POCT) is rapid usually within 30 mins and no need for lab often used in A&E although they do require health and safety, quality control records and trained staff to complete
• POCT are expensive and less robust
• there can be variation in results due to biological and analytical causes
• biological variation within indiciduals include:

  • muscular exercise - creatine kinase
  • menstrual cycle - iron
  • pregnancy - hormones
  • diet - glucose
  • time of day - cortisol (shift workers often opposite)
  • posture - protein (bed ridden = decrease)
  • drugs - oral contraceptives
  • sex - creatinine
  • age - range changes with age
  • race - some groups more at risk
• analytical variation factors include precision accuracy, sensitivity and specificity
• precision is the reproducibility of a method - all results are close but may not be correct
• accuracy is how close the measured value is to the true value
• standard deviation (SD) is the measure of scatter around the mean - and often have a gaussian distribution (roughly 67% results within mean plus/minus 1 SD, roughly 95% results within mean plus/minus 2SD, therefore roughly 5% results lie outwith the mean)
• coefficient of variation is a measure of precision or imprecision of the analysis - an acceptable CV is 5% or less
• $CV =$$(SD/mean) *$$100$

  coefficient of variation
• sensitivity is how little of analyte the method can detect (detection limits) a higher sensitivity helos discriminate between normal results and patients with the disease
• specificity is how good an assay is at discriminating between analyte and interfering substrate - test results are compared toa reference range which represents the healthy state (includes mean plus/minus 2SD)
• a healthy person has a 1:20 chance that their result will fall outside the reference range - ideally there will be no overlap but a cutoff is decided
• abnormal result ut no disease is a false positive
• a normal result by presence of the disease is a false negative
• clinical sensitivity is the proportion of positive test results in a diseased group as a percentage - aka the predictive value of a positive test

  $sensitivity =$$(TP/TP+FP) *$$100$
• clinical specificity is the proportion of negative results in a healthy group as a percentage - aka predictive value of a negative test

  $specificity =$$(TN/TN+FP)*$$100$
• cut of value lowered will increase the sensitivity but decrease specificity. cut of value increased will lower the sensitivity but increase specificity
• efficiency of a test:

  $(TP+TN/total no.ofTests)*$$100$
• performance of a method is monitored to give reassurance that the method is performing satisfactorily - use QC multiple times throughout the day (internal QC)
• west guard rules aids to interpret QC analysis - it is consistent and effective and tailored to specific assay requirements
• spread of results indicate precision and differences from the true value reflect accuracy so internal QC use high/mid/low samples to test
• external QC schemes like NEQAS where identical samples are sent to various labs, results are then compared and recorded - this also asseses internal QC of the labs
• values are asigned an all laboratory trim mean (ALTM) which removes the top and bottom 5%
• bias is the percentage deviation from a target value
• rolling bias is the mean of the current and previous 5 results
• rolling variability is the mean of the current and previous 5 results ignoring sign
• bias index state is the comparison of deviation from target values
• overall laboratory performance is the mean of BIS for all analytes
• method bias is the mean from ALTM each method
• results summary is the overview of results from the lab
• an audit is a quality improvement process - both internal and external QC assure analytical validity, also assesses pre/post method
• horizontal audit assesses one element of a process applied to 1 or more items