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Change explorer · Chemistry

Jaffe vs enzymatic creatinine on the same analyser

Public dataBuilt from a published open-access study.

Central lab analyser, enzymatic creatinine compared with same analyser, kinetic Jaffe creatinine: 529 paired results from a published study by Schmidt et al. (2015, PLoS ONE), re-analysed by NakedSignal as if one laboratory had switched from the first system to the second. At 1.2, 1.5 mg/dL, 23 results fall in a different category on the second system than on the first, against about 12 expected from repeat testing alone. That expected count uses the 1.8% imprecision the study itself measured; at that imprecision the count from repeat testing alone falls between 6 and 17 with 95% probability, so the 23 crossings are about twice the expected count, and by the exact Poisson-binomial test 23 or more from repeat testing alone has probability 0.00017. That 1.8% is also our program's laboratory-analyser default (1.79%, this study's own reported precision), so the default gives about the same count; the program's cautious point-of-care default of 6%, which it uses when a point-of-care device is involved and no precision data are supplied, would give about 41, which overstates repeat-testing noise for these laboratory analysers. At the upper end of the study's own precision estimate, 2.34%, about 15 would be expected and 23 or more has probability 0.014.

Chemistry

Creatinine, mg/dL

Central lab analyser, enzymatic creatinine compared with Same analyser, kinetic Jaffe creatinine. 529 paired results.

Compare it with the other comparisons in the explorer

Comparison line

The new system reads 0.3% higher than the old system on average. The comparison line (Passing-Bablok) has a slope of 0.939 (95% interval 0.914 to 0.967) and an intercept of 0.053.

Public data
Comparison line, creatinine (mg/dL)Comparison line with slope 0.939 (95% interval 0.914 to 0.967) and intercept 0.053, drawn against the line of no change. Decision limits drawn at 1.2, 1.5 mg/dL. Where the comparison line sits above the line of no change, the new system reads higher; below, lower.11.511.51.21.5No changeComparison lineOld system, mg/dLNew system, mg/dL

Fig. 1. The comparison line against the line of no change, over the range of the decision limits (1.2, 1.5 mg/dL). Dots mark where each line meets each limit; the gap between them is the bias at that limit.

Crossing each limit

Results that fall on the other side of a decision limit on the new system than on the old, read as if the new system had replaced the old, against the number repeat testing on one unchanged system would move. The program reports the count across all limits together.

All decision limits together (1.2, 1.5 mg/dL)

Crossed between the two systems: 23

Expected from repeat testing alone: about 12

Grade and warnings

  • Re-test band: full (at least the protocol minimum of pairs).
  • Band half-width around each limit: 7.07%.
  • Results re-tested on data the band was not fitted to, median: 15%.
  • Share of the excess crossings caught on unseen data, comparison line and band together: 90%; comparison line alone: -26%. The excess is the crossings above what repeat testing alone would cause, so the share can exceed 100% or fall below zero.
  • Repeat-test imprecision: supplied by the study, precision file (published within-device precision, source study Table 1), the larger of the two systems.

Source

Schmidt RL, Straseski JA, Raphael KL, Adams AH, Lehman CM (2015). A Risk Assessment of the Jaffe vs Enzymatic Method for Creatinine Measurement in an Outpatient Population. PLoS One. doi:10.1371/journal.pone.0143205 (opens in a new tab); PMC4657986 (opens in a new tab). Licence: CC BY 4.0 (opens in a new tab). Re-analysed by NakedSignal. The deposit names the systems.

Show the numbers
All values for creatinine, Central lab analyser, enzymatic creatinine to Same analyser, kinetic Jaffe creatinine
FieldValue
Paired results used529
Comparison line slope0.939394
Slope, 95% interval0.914273 to 0.966676
Comparison line intercept0.05303
Mean difference, new minus old, as % of old0.343
Decision limits (mg/dL)1.2, 1.5
Crossed between the two systems23
Expected from repeat testing alone11.67
Band half-width (%)7.07
Re-tested, unseen data, median (%)14.74
Re-tested, unseen data, range (%)13.99 to 15.69
Excess caught, line and band (%)90
Excess caught, line alone (%)-26.47

Related

Guide: Jaffe or enzymatic creatinine

Every study behind the explorer, with its licence: public data. How the counts are made: how it works.

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