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Change explorer · Haematology and immunology

Point-of-care haemoglobin on a CD4 analyser vs a laboratory haematology analyser

Public dataBuilt from a published open-access study.

Central lab haematology analyser compared with point of care CD4 and haemoglobin analyser: 128 paired results from a published study by Sagnia et al. (2024), re-analysed by NakedSignal as if one laboratory had switched from the first system to the second. At 8, 12, 13 g/dL, 30 results fall in a different category on the second system than on the first, against about 17 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. The deposit holds 128 pairs; the paper reports 119 and its exclusions cannot be identified, so all 128 are used.

Haematology and immunology

Haemoglobin, g/dL

Central lab haematology analyser compared with Point of care CD4 and haemoglobin analyser. 128 paired results.

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Comparison line

The new system reads 3.6% lower than the old system on average. The comparison line (Passing-Bablok) has a slope of 1 (95% interval 0.966 to 1.056) and an intercept of -0.3.

Public data
Comparison line, haemoglobin (g/dL)Comparison line with slope 1 (95% interval 0.966 to 1.056) and intercept -0.3, drawn against the line of no change. Decision limits drawn at 8, 12, 13 g/dL. Where the comparison line sits above the line of no change, the new system reads higher; below, lower.510155101581213No changeComparison lineOld system, g/dLNew system, g/dL

Fig. 1. The comparison line against the line of no change, over the range of the decision limits (8, 12, 13 g/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 (8, 12, 13 g/dL)

Crossed between the two systems: 30

Expected from repeat testing alone: about 17

Grade and warnings

  • Re-test band: full (at least the protocol minimum of pairs).
  • Band half-width around each limit: 0.84%.
  • 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: 74%; comparison line alone: 47%. 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

Sagnia B, Mbakop Ghomsi F, Moudourou S, Gutierez A, Tchadji J, Sosso SM, Ndjolo A, Colizzi V (2024). Accurate and reproducible enumeration of CD4 T cell counts and Hemoglobin levels using a point of care system: Comparison with conventional laboratory based testing systems in a clinical reference laboratory in Cameroon. PLoS One. doi:10.1371/journal.pone.0297790 (opens in a new tab); PMC10954178 (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 haemoglobin, Central lab haematology analyser to Point of care CD4 and haemoglobin analyser
FieldValue
Paired results used128
Comparison line slope1
Slope, 95% interval0.965502 to 1.055637
Comparison line intercept-0.3
Mean difference, new minus old, as % of old-3.577
Decision limits (g/dL)8, 12, 13
Crossed between the two systems30
Expected from repeat testing alone17.35
Band half-width (%)0.84
Re-tested, unseen data, median (%)14.84
Re-tested, unseen data, range (%)13.28 to 16.41
Excess caught, line and band (%)74.31
Excess caught, line alone (%)47.42

Related

Other comparisons from the same study:

Guide: Crossings by chance

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