Delta Check Calculation Guide

Transcription

1 Delta Check Calculation Guide National Technology 2017, All Rights Reserved By Senior Scientific Researcher, Asmaa Taher

2 Table of Contents Definition... 2 Purpose... 2 Delta Check Research Studies... 2 CAP Q-Probe... 2 Study conditions... 3 Observations... 3 Recommendations... 4 Actions taken... 4 Findings... 6 UAMS: University of Arkansas for Medical Science... 9 Findings... 9 Keep in mind 10 How to Calculate Delta Check Limits? Example References Page 1 of 12

3 Definition The Delta Check is a measurement of the difference between a patient s sequential test results, where a larger than expected interval change in results may indicate a testing problem associated with either the former or the current specimen and prompt an investigation before results are reported. Delta check can be expressed as the absolute or the percent difference between two consecutive results. Absolute value are calculated as the difference between the larger and smaller result. 1. Δ = X-x Percent delta are calculated as the difference between the larger result and the smaller result divided by the smaller result. 2. Δ% = (X-x)/x Where: X is the larger result / x is the smaller result Purpose 1. Delta checks are widely used in clinical laboratories as a patient-based quality assessment tool to detect errors associated with: a. Specimen collection b. Analysis c. Reporting problems 2. Provides a safety net for identifying testing errors that might otherwise go unnoticed. 3. An important component of auto-verification procedures that improve the laboratory s efficiency Delta Check Research Studies CAP Q-Probe The College of American Pathologists CAP worked on Delta Check Q-Probes study and published their results on April The goal of this Q-Probes research study is for making adjustments such as: a. Adding or removing analytes, b. Reviewing observations to determine the maximum number of days used in delta check calculations. Page 2 of 12

4 Study conditions 1. A total of 49 facilities participated in this study. 2. Among 4505 testing episodes involving 6541 delta check alerts. Testing episode: action of collecting samples and perform several tests on them. 3. The median frequencies of actions taken among 49 laboratories were: Action Taken Percentage % Clinical review 38.0 Retest of the current sample 25.0 Recheck of the current sample 20.2 Nothing 15.4 Analytical check 5.0 Other 2 Retest or check previous specimen 0 4. Time interval is the specimen collection time difference between the current and previous results. Time interval is flexible. Most hospital laboratories choose 24 or 48 hours. Maximum time interval was 14 days. 5. Delta checks are recommended for inpatient testing. Generally, you want to select the chemistry analytes that have the lowest biological variation. Observations 1. Among the 240 delta check testing problems identified, the most common were interference due to hemolysis, lipemia, or icterus, with IV fluid contamination which is somewhat less common. Analytical and other processing or handling errors represented very few of the testing problems. 2. The study authors thought of delta checks as a way of picking up misidentified specimens, but even with the large number of specimens in the study, there were only 11 instances of misidentification. Delta check is not as good for picking up mislabeling, which represented only 5% of testing problems and 0.3 % of all testing episodes % of the testing episodes involving delta checks involved no change in test results or suspected problems. Patient results were verified and released with no change. 4. What the study s authors found, when there is a delta check, some analytes are more effective at identifying problems. a. Analytes have the highest levels of relative performance: sodium, potassium, calcium, magnesium, MCV, mean corpuscular hemoglobin, Page 3 of 12

5 mean corpuscular hemoglobin concentration, red blood cell distribution width, hemoglobin or hematocrit, and platelet count. b. Less effective are: creatinine or blood urea nitrogen, albumin, chloride, phosphorus, white blood cell count, carbon dioxide, prothrombin time, and international normalized ratio of prothrombin time of blood coagulation. c. The least effective are: total protein, bilirubin (total and direct), uric acid, aspartate aminotransferase, alkaline phosphatase, glucose, lactate dehydrogenase, gamma-glutamyltransferase, and cholesterol. 5. Delta check could be either absolute, percentage, or rate of change. The laboratories contributed in the study split using absolute value (52 %) and percentage (48 %). Laboratories did report using the absolute value more often than percentage for certain analytes, such as MCV, hemoglobin, potassium, and chloride, whereas they were likelier to use percentage more often for platelets and enzymes. 6. When you have a delta check, a problem could involve either the current sample or the previous one. Nevertheless, we found that previous samples were investigated much less often compared with the current sample. This was a striking difference, with current specimens checked 36 times more often than previous specimens even though 23.8 % of testing problems involved the previous specimen. 7. There was no action taken in response to a delta check 36 % or more of the time in facilities ranked above the 75th percentile. In 10 % of the laboratories, delta checks were not investigated in almost 80 % or more of cases. Ideally, if you have a delta check, you should always do something. Recommendations 1. The study authors recommend that laboratories consider using a checklist to better standardize investigation of the delta check. 2. Many of the significant delta checks identified specimen quality issues. 3. Investigate the previous sample as well as the current sample. Actions taken Table 1. Worksheet Categories for Actions, Problems, and Outcomes Used by Participants for Collecting Information about Delta Check Alerts None taken (current or previous specimens) Repeat testing (current or previous specimens) 1. Testing repeated from primary tube Page 4 of 12

6 2. Testing repeated from original aliquot 3. Testing repeated from new aliquot 4. Performed additional (non-ordered) tests 5. Checked for ABO discrepancy Specimen check (current or previous specimens) 1. Check for hemolysis, lipemia, and icterus. 2. Check for clot 3. Check for primary tube mislabeling 4. Check for aliquot mislabeling Analytical check (current specimen) 1. Checked other results on same run 2. Checked quality control 3. Retested quality control 4. Retested specimen after recalibration 5. Retested after instrument troubleshooting Clinical review 1. Checked blood transfusion history 2. Reviewed medical record 3. Contacted clinical personnel for more information Other actions 1. Checked LIS or interface 2. Rechecked calculations 3. Checked for discrepancies with other laboratory sections 4. Reviewed with technical supervisor 5. Reviewed with pathologist/laboratory director 6. Request new specimen 7. Checked for other pre-analytical problem(s) 8. Checked for other analytical problem(s) 9. Checked for other post-analytical problem(s) Test problem(s) suspected or confirmed (current or previous specimens) Problem 1. Analytical measurement error 2. Calculation error 3. Clotted specimen 4. Data entry error 5. Clerical error, other than data entry 6. Interface/data transmission error 7. Delay in processing 8. Delay in transport 9. Hemolysis, lipemia, icterus 10. Improper handling (temperature, light) Page 5 of 12

7 11. Improper processing (dilution, aliquot) 12. Mislabeled aliquot 13. Mislabeled specimen 14. Specimen contamination (e.g., IV fluid) 15. Wrong specimen container 16. Other problem (describe below) No problem identified 1. Cause for delta check is unexplained 2. Delta check caused by physiologic condition 3. Delta check caused blood transfusion 4. No testing problem, other cause not listed for delta check Findings Thirty analytes (30) were included in the study: 1. Chemistry: CBC: 7 3. Coagulation: 3 Chemistry Page 6 of 12 Analytes Absolute Change Percentage Change % Sodium 9 meq/l 5 Calcium 2 mg/dl 15 Potassium 1 meq/l 20 Creatinine 1 mg/dl 30 BUN 20 mg/dl 50 Albumin 1 g/dl 20 Protein 2 g/dl 20 Total bilirubin 2 mg/dl 40 Chloride 10 meq/l 12 Phosphorus 2 mg/dl 50 CO2 8 meq/l 20 Magnesium 1 mg/dl 25 Uric acid 2 mg/dl 40 Direct bilirubin 2 mg/dl 80 AST Alkaline phosphatase 20 U/L 50 Glucose 100 mg/dl 50 Lactate dehydrogenase 65 c-glutamyltransferase

8 Hematology Coagulation Cholesterol 70 mg/dl 30 MCV 4 fl 6 Hemoglobin 2 g/dl 20 Platelet count /lL 34 WBC count 5 000/lL 35 Hematocrit 6% 14 MCH 4 pg --- MCHC 2 g/l --- Prothrombin time INR 1 28 Fibrinogen Page 7 of 12

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10 UAMS: University of Arkansas for Medical Science Several medical facilities worked on Delta Check study individually and published the results. Here is one example from University of Arkansas for Medical Science UAMS Findings Chemistry (serum) Analyte Albumin Bilirubin *BUN Calcium (Ca) Carbon Dioxide Chloride (Cl) *Creatinine Magnesium Osmolality Potassium (K) Sodium (Na) Total Protein **Uric Acid Delta Check 2.0 g/dl 2.0 mg/dl 25 mg/dl 3.0 mg/dl 15 meq/l 15 meq/l 10 mg/dl 2.0 meq/l 20 mosm/kg 2.5 meq/l 15 meq/l 2.0 gm/dl 2.0 mg/dl * Non-Renal ** Non-Heme/Onc Page 9 of 12

11 Keep in mind: 1. Generally studies include inpatients over 18 years old. 2. Delta check limits may change with patient age: a. MCV elevations in neonates. b. Creatinine decreases with age, urea increases. 3. Different rules may be needed for different population. Ex. oncology, transplant. 4. These conditions should be considered in investigation checklist when Delta Check alarm set off. Page 10 of 12

12 How to Calculate Delta Check Limits? Setting the alerting limits of Delta Check through calculating RCV Reference Change Value (RCV): RCV = * Z * (CV A 2 + CV I 2 ) 0.5 Z = For 2 tailed analyses: 1.96 at 95% probability ( significant ); 2.58 at 99% probability ( highly significant ) CV A = analytical variation (from QC) = SD/Mean * 100 CV I = intra-individual variation (from literature or Example Alkaline phosphatase internal QC has an SD of 0.56 U/L at a mean of 40 U/L. CV A = 0.56 / 40 * 100 = 1.4% Within subject biological variation (CV I ) is 6.4% Formula is: RCV =2 0.5 * Z * (CV A 2 + CV I 2 ) 0.5 RCV at 95% = * 1.96 * ( ) 0.5 = 18% RCV at 99% = * 2.58 * ( ) 0.5 = 24% Absolute value = Mean * RCV = 40 * 24% = 9.6 U/L This concludes the delta check calculation guide. Page 11 of 12

13 References CP?code=coap-site review,%20Dr%20C.%20Ricos.pdf Page 12 of 12