External Quality Assessment in Coagulation

External quality assessment (EQA) in coagulation is an independent evaluation of the accuracy of blood coagulation parameters. Interlaboratory comparison (proficiency testing, PT) programs cover screening tests (PT/INR, aPTT), special tests (clotting factors, antithrombin, D-dimer) and anticoagulant therapy monitoring. The accuracy of coagulation testing has a direct impact on patient safety.

Why EQA Matters in the Hemostasis Laboratory

Hemostasis testing is an area where analytical errors have immediate clinical consequences. An incorrect INR in a patient on warfarin can lead to thrombosis or bleeding. An error in D-dimer can lead to a missed pulmonary embolism.

Specific features of coagulation EQA:

Results are highly method-dependent: the thromboplastin, activator and instrument all affect the values
INR standardization is critical: different ISI systems produce different INRs
Both screening and special tests must be monitored
Anticoagulant therapy monitoring (warfarin, heparin, DOACs) directly affects dosing
GOST R ISO 15189-2024 requirement: EQA participation is mandatory for all coagulation tests

Parameters Covered

Screening Tests

Prothrombin time (PT) / INR: monitoring of vitamin K antagonist therapy, screening of the extrinsic pathway
Activated partial thromboplastin time (aPTT): screening of the intrinsic pathway, monitoring of heparin therapy
Thrombin time (TT): assessment of the final stage of coagulation
Fibrinogen: quantitative determination by the Clauss method

Special Tests

Clotting factors: II, V, VII, VIII, IX, X, XI, XII, XIII
Inhibitors: antithrombin III, protein C, protein S
Lupus anticoagulant (LA): screening and confirmation
Antiphospholipid antibodies: anticardiolipin (IgG, IgM), anti-β2-glycoprotein I

Markers of Thrombus Formation and Fibrinolysis

D-dimer: exclusion of thromboembolism, monitoring of DIC
FDP (fibrinogen/fibrin degradation products)
Soluble fibrin monomer complexes (SFMC)

Anticoagulant Therapy Monitoring

Anti-Xa activity: monitoring of LMWH (low-molecular-weight heparins) and DOACs (rivaroxaban, apixaban)
Calibrated diluted thrombin time (dTT): monitoring of dabigatran

International EQA Programs

Provider	Program	Frequency	Scope
CAP	COAG — Coagulation	3×/year	PT/INR, aPTT, fibrinogen, factors
CAP	Special Coagulation	2–3×/year	LA, antiphospholipids, inhibitors
Randox RIQAS	Coagulation	12×/year	PT/INR, aPTT, D-dimer, fibrinogen
Bio-Rad EQAS	EQAS Coagulation	12×/year	Full coagulation spectrum
INSTAND e.V.	Coagulation	2–4×/year	PT, aPTT, factors, inhibitors
INSTAND e.V.	554 Gerinnungs-Marker	4×/year	D-dimer, FDP
UK NEQAS	Blood Coagulation	Up to 6×/year	Full spectrum, including LA
Labquality	Coagulation	4–6×/year	Screening and special tests

Specific Features of Coagulation EQA

The INR Standardization Problem

The INR (international normalized ratio) is a calculated value that depends on:

EQA programs for PT/INR must provide peer grouping by instrument and reagent combination; otherwise, the comparison is invalid. CAP and UK NEQAS offer the most detailed peer grouping in this area.

The ISI (International Sensitivity Index) of the thromboplastin
Calibration of the specific instrument with the specific reagent lot
The end-point detection method (optical, mechanical)

Control Materials

Lyophilized plasma: the standard format for most programs
Liquid frozen plasma: closer to native samples, but requires a strict cold chain
Commutability: for D-dimer and special tests, compatibility of the control matrix with the method is critical

Equipment Compatibility

Coagulation analyzers from leading manufacturers are compatible with the main EQA programs:

Equipment type	Example models	Recommended EQA programs
Automated coagulation analyzers	Sysmex CS-5100, Stago STA-R Max, IL ACL TOP	CAP COAG, RIQAS, Bio-Rad, UK NEQAS
Semi-automated coagulation analyzers	Tcoag Cascade, Amelung KC	CAP COAG, INSTAND, Labquality
POCT coagulation analyzers	Roche CoaguChek, Abbott i-STAT	CAP POCT, RIQAS, INSTAND

Criteria for Choosing an EQA Program

1. Peer grouping by instrument and reagent system: mandatory for PT/INR

2. Coverage of special tests: LA, factors, inhibitors, anti-Xa

3. Round frequency: monthly monitoring (RIQAS, Bio-Rad) for screening tests

4. Clinically meaningful evaluation: the program should assess not only analytical accuracy but also clinical acceptability (for INR, whether the result falls within the therapeutic range)

5. Support for DOAC monitoring: programs for anti-Xa and dTT are increasingly in demand

6. Sample logistics: lyophilized panels are preferable for laboratories in the CIS region

Practical Recommendations

Optimal Strategy

Basic set: CAP COAG + Randox RIQAS for international accreditation plus monthly monitoring
Extended set: add UK NEQAS Blood Coagulation for special tests (LA, factors)
POCT: separate programs for portable coagulation analyzers (CAP POCT, INSTAND)

Working with Results

Analyze INR results in the context of your own instrument and reagent peer group
For D-dimer, take into account differences in units of measurement (FEU vs DDU) and methods
If aPTT shows a systematic deviation, check the reagent lot and the activator

Documentation

Keep a separate EQA log for coagulation testing
Record corrective actions linked to the specific analyte and round
Make EQA reports available to auditors, as required by ISO 15189

KombiMED's Comprehensive Approach

KombiMED supplies coagulation equipment for laboratories of any size, from semi-automated coagulation analyzers to high-throughput systems. We help laboratories enroll in international EQA programs that match the reagent systems they use.

Our specialists can help you:

Request a consultation on external quality assessment programs for your hemostasis laboratory.

Select EQA programs for screening and special coagulation tests
Ensure correct peer grouping for INR monitoring
Prepare your hemostasis laboratory for accreditation to GOST R ISO 15189-2024