ARUP's Laboratory Test Directory

Platelet Antigen 2 Genotyping (HPA-2) : 0051310

Mnemonic: HPA2

Ordering Recommendation: Assess risk for fetal and neonatal alloimmune thrombocytopenia (FNAIT). Test may be ordered for parental or fetal genotyping.
Methodology: Polymerase Chain Reaction/Fluorescence Monitoring
Performed: Mon, Thu
Reported: 2-7 days
Specimen Required: Collect: Fetal Genotyping: Amniotic fluid OR two T-25 flasks at 80 percent confluency of 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 Remarks): Lavender (EDTA), pink (K2EDTA), or yellow (ACD Solution A or B).
Parental Genotyping: Lavender (EDTA), pink (K2EDTA), or yellow (ACD Solution A or B).

Specimen Preparation: Amniotic Fluid: Transport 10 mL unspun fluid. (Min: 5 mL)
Cultured Amniocytes: Fill flasks with culture media. Transport two T-25 flasks at 80 percent confluency of cultured amniocytes filled with culture media. Backup cultures must be retained 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.

Remarks: Maternal specimen is recommended for proper test interpretation if contamination of the fetal specimen from the mother is suspected. Order Maternal Cell Contamination. Patient History Form is available on the ARUP Web site or by contacting ARUP Client Services.

Stability (collection to initiation of testing): Fetal Specimen: Ambient: 48 hours; Refrigerated: Unacceptable; Frozen: Unacceptable
Whole Blood or Maternal Cell Contamination Specimen: Ambient: 72 hours; Refrigerated: 1 week; Frozen: Unacceptable
Reference Interval:
By report
Interpretive Data: Background Information for Platelet Antigen 2 Genotyping (HPA-2):
Characteristics: Spontaneous fetal intracranial bleeding may occur in 20 percent of severe perinatal alloimmune thrombocytopenia (PAT) affected pregnancies; 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 a rare "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.
Polymorphism Tested: Glycoprotein Iba (GPIba) c.482C>T; p.T161M; the common a allele is represented by cytosine at position c.482.
Clinical Sensitivity: Unknown.
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. Specificity may be compromised by mutations in primer sites.
Informed consent: Recommended; forms are available at www.aruplab.com.

This test is performed pursuant to an agreement with Roche Molecular Systems, Inc.



Counseling and informed consent are recommended for genetic testing. Consent forms are available online at www.aruplab.com.

See Compliance Statement C: www.aruplab.com/CS
CPT Code(s): 81400