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APC resistance in neonates and infants: adjustment of the APTT-based method
U Nowak-Göttl1, B Kohlhase, H Vielhaber
1Department of Paediatrics, University Hospital Kiel, Germany.
Insights
Resistance to activated protein C (APCR) is a key cause of blood clots. This study found that a specific lab test dilution is crucial for accurately detecting the Factor V mutation in infants, preventing misdiagnosis of APCR.
Area of Science:
- Hematology
- Genetics
- Pediatrics
Background:
- Activated protein C resistance (APCR) is a significant inherited risk factor for venous thromboembolism.
- The Factor V Arg 506 Gln mutation is the most common genetic cause of APCR.
Purpose of the Study:
- To evaluate the accuracy of an activated partial thromboplastin time (aPTT)-based method for detecting the Factor V Arg 506 Gln mutation in infants.
- To determine the optimal plasma dilution for reliable APCR testing in neonates and infants.
Main Methods:
- Investigated 120 healthy infants and 24 infants with sepsis using an aPTT-based assay and DNA analysis.
- Assessed clotting times with and without activated protein C at plasma dilutions of 1:1, 1:5, and 1:11.
- Included data from 11 neonates with vascular occlusion heterozygous for the Arg 506 Gln mutation.
Main Results:
- Concordance between the aPTT-based method and DNA testing for the Factor V mutation was achieved only at a 1:11 plasma dilution (cut-off ratio < 2).
- Using lower dilutions (1:1 or 1:5) led to misclassification of APC resistance in infants without the mutation, particularly those with sepsis.
- Some infants with the mutation showed ratios > 2 at lower dilutions, indicating potential false negatives.
Conclusions:
- The 1:11 plasma dilution is essential for accurate aPTT-based detection of the Factor V Arg 506 Gln mutation in infants.
- Inappropriate dilutions can lead to misdiagnosis of APCR, especially in vulnerable infant populations like those with sepsis.
- Accurate genetic testing and optimized laboratory methods are critical for managing thrombotic risk in infants.
Abstract:
Resistance to activated protein C (APCR) has emerged as the most important hereditary cause of venous thromboembolism. Using an aPTT-based method together with DNA technique we investigated 120 healthy neonates and infants < 12 months of age and 24 infants with septicaemia for the presence of this mutation. In addition, data of 11 neonates with vascular occlusion, heterozygous (+/-) for the Arg 506 Gln mutation were included. Results of an aPTT-based method (clotting time using the APC/CaCl2 solution obtained in an undiluted, 1:5 and 1:11 dilution with factor V deficient plasma divided by clotting time with CaCl2 in the same plasma dilution) are shown: Whereas 7 (5.5%) out of 120 healthy neonates were (+/-) carriers for the factor V Arg 506 Gln mutation, concordance with the aPTT-based method (cut-off defined as ratio < 2) was found only when using the 1:11 plasma dilution. Six (four) out of 24 infants with sepsis, not carrying the factor V mutation, would have been classified as APC resistant when using the 1:1 (1:5) plasma dilution. Four (two) out of 18 patients, (+/-) for the Arg 506 Gln mutation showed APC ratios > 2 in the 1:1(1:5) plasma dilution.