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Change explorer · Chemistry

Point-of-care total cholesterol vs the central laboratory (device A)

Public dataBuilt from a published open-access study.

Central lab chemistry analyser compared with point of care device A: 329 paired results from a published study by Giachino et al. (2024), re-analysed by NakedSignal as if one laboratory had switched from the first system to the second. At 200, 240 mg/dL, 51 results fall in a different category on the second system than on the first, against about 25 expected from repeat testing alone. That expected count uses a default repeat-test imprecision, the setting our program uses when no precision data are supplied, not one measured in this study, so the two numbers are not a test of whether the switch moves more results than repeat testing would.

Chemistry

Total cholesterol, mg/dL

Central lab chemistry analyser compared with Point of care device A. 329 paired results.

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Comparison line

The new system reads 6.6% lower than the old system on average. The comparison line (Passing-Bablok) has a slope of 1.108 (95% interval 1.042 to 1.178) and an intercept of -27.449.

Public data
Comparison line, total cholesterol (mg/dL)Comparison line with slope 1.108 (95% interval 1.042 to 1.178) and intercept -27.449, drawn against the line of no change. Decision limits drawn at 200, 240 mg/dL. Where the comparison line sits above the line of no change, the new system reads higher; below, lower.100150200250300100150200250300200240No 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 (200, 240 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 (200, 240 mg/dL)

Crossed between the two systems: 51

Expected from repeat testing alone: about 25

Grade and warnings

  • Re-test band: full (at least the protocol minimum of pairs).
  • Band half-width around each limit: 4.89%.
  • Results re-tested on data the band was not fitted to, median: 14%.
  • Share of the excess crossings caught on unseen data, comparison line and band together: 58%; comparison line alone: -4%. 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: default value.

Source

Giachino M, Vetter B, Perone SA, Correia JC, Erkosar B, Heller O, Khanal VK, Lab B, Pataky Z, Poudel S, Rai M, Sharma SK (2024). Performance and usability of cardiometabolic point of care devices in Nepal: A prospective, quantitative, accuracy study. PLOS Glob Public Health. doi:10.1371/journal.pgph.0003760 (opens in a new tab); PMC11449279 (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 total cholesterol, Central lab chemistry analyser to Point of care device A
FieldValue
Paired results used329
Comparison line slope1.108033
Slope, 95% interval1.04154 to 1.177685
Comparison line intercept-27.448753
Mean difference, new minus old, as % of old-6.598
Decision limits (mg/dL)200, 240
Crossed between the two systems51
Expected from repeat testing alone25.32
Band half-width (%)4.89
Re-tested, unseen data, median (%)14.14
Re-tested, unseen data, range (%)13.07 to 15.5
Excess caught, line and band (%)57.98
Excess caught, line alone (%)-3.89

Related

Other comparisons from the same study:

Guide: Crossings by chance

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

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