Internal Quality Control in the Haemostasis laboratory. Dr Steve Kitchen Sheffield Haemophilia and Thrombosis centre & UK NEQAS Blood Coagulation

Transcription

1 Internal Quality Control in the Haemostasis laboratory Dr Steve Kitchen Sheffield Haemophilia and Thrombosis centre & UK NEQAS Blood Coagulation

2 Disclosures None

3 What is Quality Control? In a medical laboratory situation :- All the processes used to ensure results are safe to release for clinical management - valid and accurate

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5 Why do we need Quality control? Philadelphia Enquirer Aug Lab used an insensitive chemical for 7 weeks believing it to be sensitive. Patient questioned escalating coumadin dose Patient with INR bleeding from gums INR result at another site 5.7 PTs performed with ISI.8 INRs calculated with ISI.0 Amongst 932 patients - 5 deaths linked

6 Quality Assurance measures taken to ensure the reliability of laboratory sampling, testing and reporting IQC ensures precision and consistency of results for reporting EQA retrospective analysis comparing results between laboratories and between methods UK NEQAS Coagulation

7 Inaccurate and imprecise This assay is inaccurate and imprecise

8 Inaccurate but precise This assay is inaccurate but precise

9 Accurate and imprecise This assay is accurate but imprecise

10 Accurate and precise The assay producing the results shown is both accurate and precise

11 Quality control materials

12 Quality Control Material A substance used in routine practice for checking the concurrent performance of an analytical process It must be similar in properties to and be analysed along with the patient specimens ICSH 984

13 IQC materials All vials or aliquots identical Stable over period of use (lyophilised,frozen)

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15 Frequency of testing Screening tests CLSI - PT and APTT (Marlar et al 2008) At least 2 levels every 8 hours. After any reagent change. After daily maintenance. At least level every 4 hours if continuous processing.

16 IQC What level? Screening tests CLSI - PT and APTT (Marlar et al 2008) One level in normal/reference range One abnormal in clinically relevant range.

17 IQC What level? Specialist testing -batch analysis Large batches (thrombophilia etc) Two levels as for screening tests Small batches (factor assays) CLSI recommends 2 levels WFH level (preferably at the interface of normal/abnormal)

18 D e Date of Test FVIII (iu/ml) Internal Quality Control results for FVIII:C Assay Target range is mean ± 2sd of 20 determinations

19 Out of range results Single rule Single result exceeds a particular threshold triggers action. Statistically inevitable from time to time without analytical problem Multiple rules eg Westgard rules with defined criteria from multiple IQC levels/tests reduces false rejections

20 Single rule IQC out of target range? Suspend new patient testing and reporting of results since last QC result within limits. Re-test to exclude analytical error. Still out?

21 Single rule IQC out of target range? Suspend new patient testing and reporting of results since last QC result within limits. Re-test to exclude analytical error. Still out? Replace QC material and retest. Still out?

22 Single rule IQC out of target range? Suspend new patient testing and reporting of results since last QC result within limits. Re-test to exclude analytical error. Still out? Replace QC material and retest. Still out? Replace reagents and retest. Still out?

23 Single rule IQC out of target range? Suspend new patient testing and reporting of results since last QC result within limits. Re-test to exclude analytical error. Still out? Replace QC material and retest. Still out? Replace reagents and retest. Still out? Suspend method and switch to backup, and contact higher authority Maintain an error log of these interventions

24 Troubleshooting IQC Why 2 levels? PT PT 2 APTT APTT 2 problem out in out in QC material In Out In out QC 2 material out out in in PT reagent In In Out Out APTT reagent Out Out Out Out Instrument or common reagent

25 Shift following change in lot number of reagent (test strip) INR TARGET VALUES Range POC INR with excessively wide target range and showing a shift

26 IQC _APTT results showing a trend APTT (sec) Trend to higher results as a gradual change in Material, reagent or analyser

27 IQC chart APTT- Unstable IQC sample New vial of IQC 5 0 APTT (sec)

28 Stability of APTT on 2 lyophilised plasmas after reconstituion APTT (sec) Time in Min after reconstitution ph 8.6 and 8.9 indicates in adequate buffering

29 Stability of Frozen samples for FVIII assay ( stage) (Woodhams et al 200) Frozen/stored 74 o C Frozen -74 o C Stored 24 o C Frozen/Stor ed 24 o C < 5% change < 0% change 6 months 3 months 3 months 8 months 6 months 3 months

30 Internal Quality Control Point of Care INR testing

31 OBoard QC Built into test strips Currently -CUC XS and CUC XS Plus -Protime -INRatio Useful for strip integrity Not all show result and/or range Useful but not sufficient alone as IQC.

32 Electronic QC

33 Electronic QC Material Sends electrical pulse to the device Checks internal circuits are working properly Range -Level INR seconds -Level 2 INR seconds Useful but not sufficient alone as IQC.

34 POC INR Wet testing is needed? When starting a new batch of test strips Any unexpected high or low results At least one per clinic (depending on clinic size)

35 POC INR - IQC information to record Date of test Batch of IQC used Range for IQC batch Batch of test strips used Operator ID

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37 How could St Agnes miss the problem? Level IQC with target range INR Test result of 2.5 sec determined with ISI.8 should have been INR.0 (in range) Calculation done using ISI of.0 INR of.2 (in range) Problem not detected

38 How could St Agnes miss the problem? Inclusion of an abnormal IQC would have detected the error Level 2 IQC target range INR Consider IQC result of 20 sec ISI of.8 (used for analysis) = INR of 2.9 ISI of.0 (used for calculation) = INR of.8 ie Out of range suspend reporting

39 IQC for Coagulation Tests Summary QC material with similar properties to test samples More than level with adequate testing frequency Display target values Maintain a cumulative record Keep a written procedure for intervention with record of actions taken Vigilant, motivated, well informed staff!