Butyrate Measurement Audit¶
Status: YELLOW. No ready-to-adopt Tier 1 or Tier 2 butyrate method has been established for Open Enzyme. Published evidence supports one Tier 3 culture-supernatant method-transfer candidate and one separate Tier 2 stool candidate. Neither is qualified for an Open Enzyme matrix or workflow.
The measurement weakness¶
Butyrate creates three different observability problems:
- Production: did an organism and culture process produce butyrate?
- Exposure: what concentration reached stool, serum, or the intended intestinal compartment?
- Mechanism: did that exposure change ABCG2, urate flux, inflammation, or another prespecified target?
A culture-supernatant assay answers only the first question. A stool assay measures one sampled exposure matrix. Neither establishes target-compartment exposure, Q141K rescue, gout efficacy, or safety.
Current methods¶
| Method | Matrix | Evidence and boundary |
|---|---|---|
| HPLC-UV for four SCFAs plus lactate | Bacterial culture supernatant | Tier 3 transfer candidate. De Baere et al. report 210 nm detection after diethyl-ether back-extraction and acidification below pH 2, with matrix-matched calibration from 0.5–50 mM. The accessible primary abstract reports analyte-spanning LOD/LOQ ranges of 0.13–0.33/0.5–1.0 mM; it does not assign those endpoints specifically to butyrate or explicitly state “underivatized.” In Vitro analytical-method study (PMID 23542733, DOI) |
| Electrochemical fingerprints plus ANN | Human stool | Tier 2 candidate; not adopted. Gu et al. used a VBS-100 workstation, disposable G3 gold electrodes, target-specific pretreatment, voltammetric features, and an ANN. In the within-study independent 30-sample fecal test cohort versus GC-MS, butyrate MAE/RMSE/R² were 0.029 mM/0.034 mM/0.998. Butyrate bias was −0.015 mM with limits of agreement −0.065 to 0.035 mM and was statistically different from zero. Independent external replication and implementation transfer remain open. In Vitro analytical-method study (PMID 42041444, DOI) |
| Butyrate or SCFA ELISA | Vendor-claimed matrices | RED-provisional. No qualifying primary method comparison surfaced in the bounded COMP-038 search. This is not an exhaustive absence claim. |
| Breath hydrogen or methane | Breath | Not butyrate-specific. A broad fermentation or transit proxy, not quantitative butyrate measurement. |
| Generic free-fatty-acid colorimetry | Vendor-dependent | Wrong assay class for the reviewed use. The representative protocol excluded short-chain fatty acids including butyrate. |
HPLC-UV is Tier 3 under the quantification ladder. GC-MS is Tier 3 when run in-house and Tier 4 when a qualified external laboratory supplies the result and audit trail. Relative affordability does not change the tier. If lower-tier access is not qualified for the exact analyte and matrix, use a Tier 3 method directly.
Falsification gates¶
Culture-supernatant production QC¶
Validation §1.31 tests one exact strain, medium, and harvest workflow with matrix-matched standards, spike/recovery, interference controls, and paired HPLC-UV/GC-MS measurements. A pass qualifies only that Tier 3 implementation and matrix.
Stool monitoring¶
Validation §1.45 tests the complete Gu hardware–chemistry–model stack. It separates analytical reproduction from a later independent external transfer of a locked implementation. A pass would not transfer to culture supernatant, serum, another metabolite, or a clinical diagnostic.