Initial test for factor 13 deficiency
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Factor XIII deficiency initial screening test clot solubility urea
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Here is a complete answer on the initial test for Factor XIII (FXIII) deficiency:
Initial Test for Factor XIII Deficiency
Key Point: Routine Coagulation Tests Are Normal
Factor XIII deficiency is unique because PT, aPTT, thrombin time (TT), fibrinogen, platelet count, and bleeding time are all normal. This means standard coagulation screening will not flag it. - Tietz Textbook of Laboratory Medicine, 7th Ed.; Goldman-Cecil Medicine
The Initial Screening Test: Urea Clot Solubility Test (Clot Stability Test)
The 5 M urea clot solubility test (also called the urea clot lysis test) is the classic initial screening test for FXIII deficiency.
How it works:
- A fibrin clot is formed from the patient's plasma using thrombin and calcium.
- The clot is then placed in 5 M urea (or alternatively 1% monochloroacetic acid).
- In a normal individual, Factor XIII cross-links fibrin, making the clot stable and resistant to dissolution.
- In severe FXIII deficiency, the clot lacks cross-linking and dissolves within 1-2 hours in urea -- a positive (abnormal) result.
Principle: 5 M urea disrupts non-covalent hydrogen bonds between fibrin strands. Only Factor XIIIa-catalyzed covalent cross-links (gamma-glutamyl-lysine bonds) can resist this -- so dissolution confirms absence of cross-linking, i.e., FXIII deficiency. - Quick Compendium of Clinical Pathology, 5th Ed.
Limitations of the Urea Clot Solubility Test
| Limitation | Detail |
|---|---|
| Detects only severe deficiency | Only picks up activity <1-5% of normal; misses mild/moderate cases and heterozygous carriers |
| False positives | Hypofibrinogenemia and dysfibrinogenemia also cause clot dissolution |
| Poor sensitivity/specificity | Results vary between institutions |
| Not quantitative | Cannot measure the degree of deficiency |
Confirmatory / Follow-up Testing
If the urea clot solubility test is positive, confirmation is done with:
- Quantitative FXIII activity assay -- chromogenic/functional assay (monodansylcadaverine or putrescine incorporation assay) - this is the preferred method
- FXIII antigen (immunologic) assay -- measures FXIII-A and FXIII-B subunit levels
Quantitative activity assays are now preferred as the primary diagnostic method in settings where they are available, given the poor sensitivity of the clot solubility test. - StatPearls - FXIII Deficiency
Summary Table
| Test | Result in FXIII Deficiency |
|---|---|
| PT | Normal |
| aPTT | Normal |
| Thrombin time | Normal |
| Fibrinogen | Normal |
| Urea clot solubility test | Abnormal (clot dissolves in 1-2 hrs) |
| FXIII activity assay | Low (confirms diagnosis) |
Bottom line: The urea clot solubility test is the classical initial/screening test for Factor XIII deficiency, but it only detects severe deficiency. Quantitative FXIII activity assays are preferred where available and are required for confirmation. - Tietz Textbook of Laboratory Medicine, 7th Ed.; Mulholland & Greenfield's Surgery, 7th Ed.
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