The factor that locks the clot — and a method that can let it slip.
Factor XIII cross-links fibrin and binds α2-antiplasmin into the clot, giving it mechanical strength and resistance to lysis. It is invisible to PT and aPTT: a patient with severe FXIII deficiency can have a normal screen and still bleed, with delayed wound bleeding, poor healing or intracranial haemorrhage. The catch is in the measurement. The common ammonia-release assays overestimate activity at the low end unless a plasma blank corrects for the background, and that is exactly where the diagnosis is made. Technoclone's Technochrom FXIII (chromogenic, ammonia-release), Technofluor FXIII (fluorogenic) and FXIII deficient plasma cover this work — we advise on running the assay so a severe deficiency cannot hide.
The same low FXIII sample, read with and without an iodoacetamide plasma blank. The blank corrects the background reaction that otherwise inflates the reading at the diagnostic low end.
Illustrative — schematic, not data
Without an iodoacetamide plasma blank the sample reads ~10% of normal; with the blank applied it reads 2.4% — moving it below the severe-deficiency threshold of <5% (<0.05 IU/mL).
A normal coagulation screen does not exclude severe FXIII deficiency. An unblanked assay can then miss it a second time.
Where the assay can mislead, and how the method is fixed.
FXIII has less head-to-head literature than Factor VIII or ADAMTS13, but the dominant pitfall is well documented and method-level. The named comparator is Berichrom FXIII (Siemens); both are ammonia-release chromogenic assays, so the same plasma-blank principle applies to each.
Ammonia-release methods overestimate low FXIII activity when run without an iodoacetamide plasma blank — the unblanked background reaction inflates the reading exactly in the range that matters for diagnosis.
The plasma-blank effect is the strong, well-documented anchor: Durda 2018 puts the unblanked overestimation at up to 0.02–0.15 IU/mL. There is no single agreed figure for the separate ammonia-versus-amine method comparison, so that difference is treated qualitatively.
With the iodoacetamide blank applied, a sample read at ~10% dropped to 2.4% (p<0.0001) — the correction is what lets the assay detect severe deficiency below 5%. Without it, a severe deficiency can read as near-normal.
Severe FXIII deficiency is <5% (<0.05 IU/mL). The ~10% → 2.4% shift moves a single sample from apparently mild to clearly severe: a decision-changing difference driven entirely by the plasma blank.
Across the measuring range the two ammonia-release chromogenic assays show good agreement, with Technochrom showing slightly higher imprecision at the low, pathological end. On the method that matters most — the low end — both depend on the plasma blank to read truthfully.
Lawrie 2010 is a full method-comparison reporting good agreement between the two assays; we no longer attach a single correlation coefficient, since the paper characterises agreement without one headline R². No source URL is held for this citation, so it is shown as plain text. Neither assay is "the best" — the comparison is method-fair, and the limiting step is shared.
Technofluor FXIII offers a fluorogenic read-out as an alternative chemistry to the ammonia-release route. We name it for completeness. The one published clinical validation of Technofluor FXIII (Leitner et al. 2021, PMC7863959) is authored by Technoclone-affiliated scientists — a manufacturer validation, not independent evidence — and we say so rather than imply a neutral study exists.
The one published clinical validation of Technofluor FXIII (Leitner et al. 2021, PMC7863959) is authored by Technoclone-affiliated scientists, so we treat it as a manufacturer validation rather than independent evidence. The blank-correction evidence above applies to ammonia-release chromogenic assays; the fluorogenic chemistry is a different method. Treat the validation question openly when specifying the assay.
Across the literature there is less FXIII head-to-head work than for Factor VIII or ADAMTS13. We present what is solid — the plasma-blank effect and the severe-deficiency threshold — and flag what is approximate or absent.
The product, the method, and where judgement sits.
FXIII activity is most often measured by the ammonia-release (chromogenic) principle: activated FXIII drives a transglutaminase reaction whose ammonia by-product is coupled to an NAD(P)H-linked read-out. The diagnostic decision turns on running it with the plasma blank.
The products
Technochrom FXIII (chromogenic, ammonia-release), Technofluor FXIII (fluorogenic), and FXIII deficient plasma for calibration, controls and assay set-up.
The method that matters
Run the ammonia-release assay with an iodoacetamide plasma blank. Without it, the low end reads high and a severe deficiency can pass as mild. That is the difference between a normal screen and a missed diagnosis.
What elixir does
As UK partner for Technoclone, we represent the reagents and deficient plasma and advise on assay set-up, the plasma blank, calibration and the reporting cut-offs. Any modelling or computational work we offer is a human-led service, scoped per laboratory — never a product on the shelf.
Where another method or assay is the better answer for your laboratory, we say so.
Every figure, traceable.
- Ammonia-release methods overestimate low FXIII activity without an iodoacetamide plasma blank — by up to 0.02–0.15 IU/mL — Durda MA, Wolberg AS, Kerlin BA. State of the Art in Factor XIII Laboratory Assessment. Transfus Apher Sci 2018. PMC6289705. (The separate ammonia-versus-amine method bias has no single agreed figure.)
- With the iodoacetamide blank, a sample read 10.1% → 2.4% (p<0.0001), enabling detection of severe <5% — Cini 2016, Clin Chem Lab Med 54(5):805 — PMID 26457781.
- Berichrom (Siemens) vs Technochrom: good agreement across the range, with Technochrom slightly higher imprecision at the low pathological control — Lawrie AS, et al. Factor XIII — an under-diagnosed deficiency — are we using the right assays? JTH 2010;8(11):2478–82. (No source URL held — cited as text.)
- Severe FXIII deficiency <5% (<0.05 IU/mL) — clinical threshold used above.
Caveats carried on this page: the Technochrom–Berichrom agreement is reported qualitatively (no single headline correlation coefficient); the only Technofluor validation (Leitner 2021) is manufacturer-affiliated, not independent; FXIII has less head-to-head literature than Factor VIII or ADAMTS13. Figures shown in the signature visual are illustrative and schematic, not pooled patient data.
Specifying FXIII testing, or the reagents behind it?
Send a short note about the assay, the deficient plasma, or the blank-correction question in front of you. We will reply with how we would approach it, what it would involve, and an honest quote — usually within two working days.