Jaffe or enzymatic creatinine: what a method change does at the decision lines

Two chemistries on one analyser, read as a method change, at the study’s own precision

In the outpatient study, both chemistries ran on the same samples on the same analyser [Schmidt et al., 2015, PLoS ONE]. Our run treats the enzymatic method as the current one and the Jaffe method as the new one. Across 529 pairs, 23 results changed category, 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. Separating the crossings seen at a decision limit into the part imprecision alone would give and the part due to the change is a published procedure (Schmidt et al., 2015, Clin Chim Acta), which the creatinine study we use applies. What we add is a program that runs it on a laboratory’s own comparison and precision data at its own decision limits, keeps the re-test list in the laboratory and releases files designed to carry only aggregates. The comparison line (Fig. 2) has a slope of 0.94 (95% interval 0.91 to 0.97), so the difference is small at the lines but not zero. The paper reports no overall mean difference in creatinine; a Deming or least-squares fit to the same pairs gives a slope close to one, and the lower Passing-Bablok slope reflects curvature at low creatinine.

Point of care against the laboratory: more to manage

The point-of-care comparisons are a different kind of change: a device outside the laboratory, often on capillary blood, against a laboratory method. KDIGO supports point-of-care creatinine where laboratory access is limited, provided the same quality criteria, including external quality assessment, apply [KDIGO, 2024].

• A point-of-care meter against a laboratory Jaffe method in people living with HIV: the authors report substantial agreement and a small eGFR bias that changes direction across the range [Msilanga et al., 2025]. Here 29 results changed category against about 19 expected (default CV), at 106.08 and 132.6 µmol/L (the same two lines in SI units).
• A point-of-care device against a central laboratory analyser: the authors report a small negative average bias within recommended limits [Giachino et al., 2024]. Here 46 results changed category against about 16 expected (default CV).
• Two devices against a laboratory kinetic Jaffe method in field conditions: the authors found the venous analyser agreed well and the capillary meter read higher, especially at higher values [Krisher et al., 2024]. The venous analyser moved 1 result against about 1 expected (default CV); the capillary meter moved 28 against about 1 (default CV). Both comparisons are small, so their re-test bands are graded indicative.

Each comparison has its own page with its comparison line, re-test band and full numbers (links in the table under Fig. 1), and all of them sit side by side in the change explorer.

Choosing the lines

The creatinine lines in these comparisons (1.2 and 1.5 mg/dL) are set once across the public set so every series reads the same way. Clinical guidelines work in eGFR categories, which need age and sex with each result. A laboratory running its own comparison names the lines its clinicians use, for creatinine, eGFR or both, before the results are opened.

Related questions

• Paediatrics. Children have low creatinine, where non-creatinine chromogens weigh most in the Jaffe method [KDIGO, 2024]. A paediatric service needs a paediatric comparison; none of the public series here is one.
• Choice of eGFR equation. The equation moves eGFR categories independently of the creatinine method, so an equation change deserves its own count.
• Specific interferents. Which drugs or substances affect which method is a question for interference studies; paired patient comparisons show their combined effect.

Sources

1. 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. pmc.ncbi.nlm.nih.gov/articles/PMC4657986/
2. Myers GL, Miller WG, Coresh J, et al. (2006). Recommendations for improving serum creatinine measurement: a report from the Laboratory Working Group of the National Kidney Disease Education Program. Clinical Chemistry. doi.org/10.1373/clinchem.2005.0525144
3. Levin A, Ahmed SB, Carrero JJ, et al. (2024). Executive summary of the KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease: known knowns and known unknowns. Kidney International. kdigo.org/wp-content/uploads/2017/02/KDIGO-2024-CKD-Guideline-Executive-Summary.pdf
4. Giachino M, Vetter B, Perone SA, et al. (2024). Performance and usability of cardiometabolic point of care devices in Nepal: A prospective, quantitative, accuracy study. PLOS Global Public Health. pmc.ncbi.nlm.nih.gov/articles/PMC11449279/
5. Msilanga D, Muiru A, Msangi E, et al. (2025). PLoS ONE. pmc.ncbi.nlm.nih.gov/articles/PMC12425315/
6. Krisher L, Jaramillo D, Dye-Robinson A, et al. (2024). Application and comparison of point-of-care devices for field evaluation of underlying health status of Guatemalan sugarcane workers. PLOS Global Public Health. pmc.ncbi.nlm.nih.gov/articles/PMC11265697/