Assess risk for fetal and neonatal alloimmune thrombocytopenia. May be ordered for parental, fetal, or neonatal genotyping.
- Patient Preparation
- Fetal Genotyping: Amniotic fluid OR cultured amniocytes. If the client is unable to culture amniocytes, this can be arranged by contacting ARUP Client Services at (800) 522-2787.
WITH Maternal Cell Contamination Specimen (see Note): Lavender (EDTA), Pink (K2EDTA), or Yellow (ACD Solution A or B).
Parental Genotyping: Lavender (EDTA).
- Specimen Preparation
- Amniotic Fluid: Transport 10 mL unspun fluid. (Min: 5 mL)
Cultured Amniocytes: Transport two T-25 flasks at 80 percent confluency filled with culture media. Backup cultures must be retained at the client's institution until testing is complete.
Maternal Cell Contamination Specimen: Transport 3 mL whole blood. (Min: 1 mL)
Whole Blood (Parental Genotyping): Transport 3 mL whole blood. (Min: 1 mL)
- Storage/Transport Temperature
- Amniotic Fluid: Room temperature.
Cultured Amniocytes: CRITICAL ROOM TEMPERATURE. Must be received within 48 hours of shipment due to liability of cells.
Whole Blood or Maternal Cell Contamination Specimen: Refrigerated.
- Unacceptable Conditions
- Fetal Specimen: Ambient: 48 hours; Refrigerated: Unacceptable; Frozen: Unacceptable
Whole Blood or Maternal Cell Contamination Specimen: Ambient: 72 hours; Refrigerated: 1 week; Frozen: Unacceptable
Characteristics: Spontaneous fetal intracranial bleeding may occur in 20 percent of pregnancies affected with severe perinatal alloimmune thrombocytopenia (PAT); there is a risk of fetal death. Post-transfusion purpura may occur in transfusion recipients with antibodies to a specific platelet antigen.
Incidence: PAT occurs in 1 in 5000 births.
Inheritance: For women homozygous for the less common "b" HPA allele with antibodies to the common "a" allele, there is a 50 percent risk a pregnancy will be affected if her partner is heterozygous for the "a" allele and 100 percent risk if her partner is homozygous for the "a" allele.
Cause: Maternal-fetal HPA incompatibility.
Polymorphisms Tested: HPA-1 (ITGB3, GPIIIa) c.176T>C, p.L59P; HPA-2 (GP1BA, GPIba) c.482C>T, p.T161M; HPA-3 (ITGA2B, GPIIb) c.2621T>G, p.I874S; HPA-4 (ITGB3, GPIIIa) c.506G>A, p.R169Q; HPA-5 (ITGA2, GPIa) c.1600G>A, p.E534K; HPA-6 (ITGB3, GPIIIa) c.1544G>A, p.R515Q; HPA-15 (CD109, CD109) c.2108C>A, p.S703Y
Clinical Sensitivity: Variable, dependent on ethnicity.
Methodology: PCR followed by fluorescent monitoring.
Analytic Sensitivity and Specificity: 99 percent.
Limitations: Bloody amniotic fluid specimens may give false-negative results because of maternal cell contamination. Diagnostic errors can occur due to rare sequence variations.
Informed consent: Recommended; forms are available at www.aruplab.com.
|PA 1-6, 15 Polymorphism|
|HPA System||"a" Allele Common||"b" Allele Variant|
Counseling and informed consent are recommended for genetic testing. Consent forms are available online.
|Component Test Code*||Component Chart Name||LOINC|
|3001171||Platelet Antigen Geno Interpretation|
|3001173||Platelet Antigen 1 Genotyping|
|3001174||Platelet Antigen 2 Genotyping|
|3001175||Platelet Antigen 3 Genotyping|
|3001176||Platelet Antigen 4 Genotyping|
|3001177||Platelet Antigen 5 Genotyping|
|3001178||Platelet Antigen 6 Genotyping|
|3001179||Platelet Antigen 15 Genotyping|
|3001180||Platelet Antigen Geno Specimen|
- HPA platelet antigen genotyping panel