Traditional approaches to Reference Intervals

Transcription

1 Establishing reference intervals: Unique challenges for the pediatric population Amy L. Pyle, PhD, DABCC Traditional approaches to Reference Intervals Decision Limits Establish Verify Transfer 1

2 Decision Limits Set by national and international consensus groups for certain analytes Cholesterol, HbA1C guidelines Labs can adopt these Manufacturer should demonstrate traceability and verify accuracy Little R, Rohlfing C. HbA1c. An overview of current analytical testing issues. Clin Lab News. 2011;37(2):8 10 Establishing Intervals Lower and upper limits for the central 95% of the normal/study population 5% of normal persons will fall outside the interval Parametric estimation: assumes Gaussian distribution Non parametric: no assumptions about distribution 2

3 Results Distribution: Gaussian Central 95% Parametric Method of Interval Establishment: Central 95% of normal results is Reference Interval Not recommended, as most distribution is not Gaussian. Results Distribution: Non Gaussian Non Parametric method is preferred. For small sample size, use robust method (CLSI C28 A3c). 3

4 Establishing Intervals CLSI C28 A3c endorses this method as the best way for labs to generate RI s 120 samples for each partition (age, gender) Not practical for most laboratories Partitioning Partitions are characteristics of the population which can be used to break the reference intervals into subgroups. Partitioning between subgroups is warranted when the means between two groups are significantly different Most commonly age and gender Others: blood type, circadian variation, exercise, posture, menstrual stage, pregnancy 4

5 Verify Ranges CLSI C28 A3c recommends this as a more reasonable approach to reference intervals Requires a few as 20 samples from healthy individuals If 90% (18/20) samples are within the tested range, then that range can be accepted. If 2 3 samples are out of the range, re examine samples and analytical method. If >3 samples are out of the range, lab should consider establishing its own range Methodology Considerations Method specific Sodium = Sodium = Sodium TSH TSH TSH When finding ranges to verify, be sure to consider the methodology used to establish those ranges Immunoassay vs. mass spec Variation between manufacturers Use CAP peer group data for a rough idea of how methods compare 5

6 Use CAP Participant Summaries Use CAP Participant Summaries Caveats: No CAP survey, no method peer group From K C

7 Verify Ranges Are there even good pediatric reference ranges out there to verify? Soldin SJ, Wong EC, Brugnara C, Soldin OP, eds. Pediatric Reference Intervals, 7 th ed. Washington D.C.: AACC Press; 2011 Ashwood ER, ed. ARUP s Guide to Pediatric Clinical Laboratory Testining, 3 rd ed. Salt Lake City, UT: ARUP Laboratories; 2004 Meites S, ed. Pediatric Clinical Chemistry: Reference Values, 3 rd ed. Washington D.C.: AACC Press; Literature searches Do you have to verify ALL the partitions? Transfer Ranges Particularly useful when changing methodologies or adapting a reference interval from another methodology Need to establish comparability of assays Run method validation (see CLSI EP09) Linear Regression Slope ~ 1.0, Intercept ~0.0, correlation ~1.0: Accept ranges Intercept ~0.0, Correlation ~1.0: Correct ranges based on slope (bias) 7

8 Transfer Ranges Test X: Gold Standard Method Reference Interval: g/dl Run method comparison to new method: Transfer Ranges Test X: Gold Standard Method Reference Interval: g/dl Run method comparison to new method: 8

9 Transfer Ranges Test X: Gold Standard Method Reference Interval: g/dl Run method comparison to new method: Slope is nearly 1.0, intercept is nearly 0.0, correlation = Transfer Gold Standard Method Range to New Method Transfer Ranges Test Y: Gold Standard Method Reference Interval: g/dl Run method comparison to new method: 9

10 Transfer Ranges Test Y: Gold Standard Method Reference Interval: g/dl Run method comparison to new method: Slope is nearly 0.87, intercept is low, correlation = Apply slope to Gold St. Interval: 50 x 0.87= x 0.87 = What s unique about pediatric reference intervals? Kids aren t little adults Different metabolism Analytes changes during growth and maturation 10

11 What s unique about pediatric reference intervals? Analytes changes during growth and maturation What s unique about pediatric reference intervals? Need to partition by ages and gender What about Tanner Stages? Developmental stages, not age Particularly useful for evaluating analytes known to change during sexual maturation Requires thorough physical exam to determine 11

12 Challenges in Pediatric Reference Intervals Difficult to get lots of samples from truly normal children Especially across different age groups Small sample volumes Hoffman approach Real Life Example New Developments Difficult to get truly normal samples Could do a call for normal samples and bank them for future use Logistically challenging and expensive PRRC and National Children s Study 12

13 Difficult to get truly normal samples Could do a call for normal samples and bank them for future use Logistically challenging and expensive PRRC and National Children s Study Identify outpatients who are having routine lab work AAP screening recommendations Make sure tube types are compatible! American Academy of Pediatrics Screening Recommendations 13

14 Difficult to get truly normal samples Could do a call for normal samples and bank them for future use Logistically challenging and expensive PRRC and National Children s Study Identify outpatients who are having routine lab work AAP screening recommendations Make sure tube types are compatible! Normal results for a related parameter RetHe: samples with normal H&H, MCV, Ferritin Hoffman approach Use results from samples ordered for the test of interest (in and out patients) Better for validating, rather than establishing ranges Courtesy of Patti Jones 14

15 Real Life Example: IPF Switching TSH methodology within lab Previous ranges: Age 0 7 days 7 days 1 mo 1 mo 1 yr 1 yr 11 yr >11 yrs TSH (miu/ml) We don t know exactly where these came from! (REMINDER: Keep clear documentation of reference interval studies! Should be part of new assay validation information.) Real Life Example: TSH 15

16 Compare to CAP Peer Groups From K C 2012 Real Life Example: TSH 16

17 Real Life Example: TSH Use Slope as Multiplier Previous Ranges Age TSH (miu/ml) 0 7 days 7days 1 mo 1mo 1 yr 1 yr 11 yr >11 yrs X 0.87 Ranges multiplied by slope Age TSH (miu/ml) 0 7 days 7days 1 mo 1mo 1 yr 1 yr 11 yr >11 yrs Real Life Example: TSH Verify this by establishing range for one partition Previous Ranges Age TSH (miu/ml) 0 7 days 7days 1 mo 1mo 1 yr 1 yr 11 yr >11 yrs Choose 0 7 day group, since infants are routinely screened for elevated bilirubin (and we already made sure that icterus wouldn t interfere) Ran ~120 samples 17

18 Real Life Example: TSH Previous Ranges Age TSH (miu/ml) 0 7 days 7days 1 mo 1mo 1 yr 1 yr 11 yr >11 yrs X 0.87 Ranges multiplied by slope Age TSH (miu/ml) 0 7 days 7days 1 mo 1mo 1 yr 1 yr 11 yr >11 yrs Established Range 18

19 Real Life Example: TSH Ranges were generated!! Adult reference interval was verified using 20 healthy donors from the lab Physicians were consulted and notified (CAP All Common Checklist COM.40800) Direct to all endocrinologists Notice in the hospital wide newsletter Real Life Example: IPF Our lab wants to start offering IPF How do we establish our reference intervals? Significant logistical hurdles (Sample stability: 8 hrs) Very few other labs are offering this assay Totally novel assay (no method comparison) What reference range should we use? 19

20 Real Life Example: IPF What reference intervals should we use? Look to other labs & to the literature % % % Go through the options to create ranges: Establish Verify Transfer Real Life Example: IPF Establishing a range/verify a range It is still impractical to get 120 samples, but we did manage to get 54 samples Central 95% (parametric)= %, Transformed parametric = % Is the upper end too high? 20

21 Hoffman approach Use results from samples ordered for the test of interest (in and out patients) Better for validating, rather than establishing ranges Courtesy of Patti Jones Real Life Example: IPF All patients with samples run in optical platelet chamber (until we had ~300 results) Take central 50% of results % Take central 95% of results Courtesy of Patti Jones 21

22 Real Life Example: IPF Clinical Correlation Use residual sample 167 patients with low PLTC Sorted based off of diagnosis 33 peripheral destruction M= decreased production M= abnormal distribution M= other M=11.4 Findings consistent with previous studies Courtesy of Patti Jones Real Life Example: IPF Our range studies are fairly consistent Final range: % 22

23 Summary Creating reference intervals Establish (120 samples/partition) Verify Transfer References CLSI. Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory; Approved Guideline Third Ed. CLSI document C28 A3c. Wayne, PA: Clinical and Laboratory Standards Institute;

24 Thanks! 24