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Quality Assessment

Quality Assessment. What is Quality Control?. Quality Control in the clinical laboratory is a system designed to increase the probability that each result reported by the laboratory is valid and can be used with confidence by the physician making a diagnostic or therapeutic decision.

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Quality Assessment

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  1. Quality Assessment

  2. What is Quality Control? • Quality Control in the clinical laboratory is a system designed to increase the probability that each result reported by the laboratory is valid and can be used with confidence by the physician making a diagnostic or therapeutic decision.

  3. Control Materials • Control Values • Initially use manufacturer’s insert as guidelines • Clinical Laboratory Improvement Amendments (CLIA) requires that each Lab perform their own study to set limits • Recommend minimum 20 measurements • Over a 2 week period or 10 working days • Should be processed the same way as patient samples

  4. Investigate • When results are out of control, • You must resolve the problem • Not just go past it without knowing the cause • Especially true for systematic errors

  5. Stop bad habits!!! • Just repeating the control or just opening a new control without investigating • Most often eliminates the immediate problem but not the real problem

  6. Develop good habits • Inspect the charts • Random or systematic error? • Identify type of error with potential cause(s) • Relate possible causes to recent changes • Verify the solution and document!!

  7. Control specimen is “out of control?” • “Out of control” means that there is too much dispersion in your result compared with the rest of the results – it’s “weird” • This suggests that something is wrong with the process that generated that observation • Patient test results cannot be reported to physicians when there is something wrong with the testing process that is generating inaccurate reports • Remember … No information is better than wrong information

  8. Control specimen is “out of control?” • Things that can go wrong and what to do: ie. Corrective methods • Instrumentation malfunction ( fix the machine) • Reagents deteriorated, contaminated, improperly prepared or simply used up (get new reagents) • Tech error (identify error and repeat the test) • Control specimen is deteriorated or improperly prepared (get new control)

  9. Random or systematic • 13S and R4S usually associated with random error • 22S, 41S, and 10X most often associated with systematic errors

  10. LJ Control Charts A LJ Control Chart depend on the use of IQC specimens and is developed in the following manner: • Put up the IQC specimen for at least 20 or more assay runs and record down the O.D./cut-off value or antibody titre (whichever is applicable). • Calculate the mean and standard deviations (s.d.) • Make a plot with the assay run on the x-axis, and O.D./cut-off or antibody titre on the y axis. • Draw the following lines across the y-axis: mean, -3, -2, -2, 1, 2, and 3 s.d. • Plot the O.D./cut-off obtained for the IQC specimen for subsequent assay runs • Major events such as changes in the batch no. of the kit and instruments used should be recorded on the chart.

  11. Reference Ranges • Results are most typically interpreted with respect to the range of values found in normal, clinically healthy individuals. • A result is considered abnormal if the value is less than the lower limit of the normal range or is greater than the upper limit. • Reference ranges are determined from measurements on specimens from a large number (several hundred) of clinically normal individuals.

  12. Reference Ranges The reference range (or reference interval) for a laboratory test is a reference point to determine whether a disease is present or absent or if the patient is at risk for future disease states. This comparison may be used in monitoring the progression of a disease or therapeutic drug levels. Reference ranges may need to be established or confirmed when a new analyte is measured, a new or different analytical method is introduced, or there has been a significant reagent modification by the manufacturer. Laboratories are urged by manufacturers, as well as required by (Clinical Laboratory Improvement Amendments ) CLIA , to establish their own reference ranges.

  13. Establishment of Reference Ranges • Each lab must establish its own reference ranges • Factors affecting reference ranges • Age • Sex • Diet • Medications • Physical activity • Pregnancy • Personal habits ( smoking ) • Geographic location ( altitude ) • Body weight • Laboratory instrumentation ( methodologies ) • Laboratory reagents reference ranges are defined as being within 2 Standard Deviations from the mean

  14. Establishment of Reference Ranges A minimum of 20 observations should be sampled in order to obtain valid results ( but I’ll use just 6 to save time ) Determine the normal range for fasting plasma glucose using 6 people: Sample 1 = 98 mg/dl Mean = 102 mg/dl Sample 2 = 100 mg/dl SD = 3.0 mg/dl Sample 3 = 105 mg/dl 2 SD = 6.0 mg/dl Sample 4 = 106 mg/dl Sample 5 = 102 mg/dl Sample 6 = 101 mg/dl That means that the normal range for this group is from 102 ± 6, or 94 – 108, which is ± 2.0 SD from the mean

  15. Levey-Jennings QC Practice Exercise: Cholesterol example where:  Control 1 has a mean of 200 mg/dL and standard deviation of 4.0 mg/dL.  Control 2 has a mean of 250 mg/dL and standard deviation of 5.0 mg/dL.  Prepare appropriate control charts and interpret the results.

  16. Problem 1 • Calculation of Sensitivity and Specificity Alpha-fetoprotein (AFP) levels are used by obstetricians to help diagnose neural tube defects (NTD) in early pregnancy. For the following data, calculate the sensitivity & specificity of AFP for detecting NTD • NUMBER OF PREGNANCIES INTERPRETATION OF AFP FINDINGS

  17. Problem 2 • For the following precision data, calculate the mean, standard deviation, and coefficient of variation for each of the two control solutions A and B. These control solutions were chosen because their concentrations were close to medical decision levels (X,) for glucose: 120 mg/dL for control solution A and 300 mg/dl. for control solution B. • Control solution A was analyzed daily, and the following values were obtained: 118, 120, 121, 119, 125, 118, 122, 116, 124, 123, 117, 117, 121, 120, 120, 119, 121, 123, 120, and 122 mg/dL • Control solution B was analyzed daily and gave the following results: 295, 308, 296, 298, 304, 294, 308, 310, 296, 300, 295. 303, 305, 300, 308, 297, 297, 305, 292, and 300 mg/dL

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