Platelet Antigen 4 Genotyping (HPA-4)
0051490
Ordering Recommendation
Assess risk for fetal and neonatal alloimmune thrombocytopenia (FNAIT). Test may be ordered for parental or fetal genotyping.
Mnemonic
HPA4
Methodology
Polymerase Chain Reaction/Fluorescence Monitoring
Performed
Mon, Thu
Reported
2-7 days
New York DOH Approval Status
This test is New York DOH approved.
Submit With Order
ARUP Consult®
Disease Topics
Specimen Required
- Patient Preparation
- 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. - Unacceptable Conditions
- 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
- 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 4 Genotyping (HPA-4):
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 IIIa (GPIIIa) c.506G>A; p.R169Q; the common "a" allele is represented by glutamine at position c.506.
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. Diagnostic errors can occur due to rare sequence variations.
Informed consent: Recommended; forms are available at www.aruplab.com.
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 IIIa (GPIIIa) c.506G>A; p.R169Q; the common "a" allele is represented by glutamine at position c.506.
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. Diagnostic errors can occur due to rare sequence variations.
Informed consent: Recommended; forms are available at www.aruplab.com.
Compliance Statement C: For human genetic inheritable conditions and mutations. This test was developed and its performance characteristics determined by ARUP Laboratories. The U. S. Food and Drug Administration has not approved or cleared this test; however, FDA clearance or approval is not currently required for clinical use. The results are not intended to be used as the sole means for clinical diagnosis or patient management decisions.
Counseling and informed consent are recommended for genetic testing. Consent forms are available online.
Counseling and informed consent are recommended for genetic testing. Consent forms are available online.
Components
| Component Test Code* | Component Chart Name | LOINC |
|---|---|---|
| 0051489 | Platelet Antigen 4 Genotyping | |
| 0051491 | Platelet Antigen 4 Interpretation | |
| 2001323 | Platelet Antigen 4 Specimen |
Aliases
- HPA 4 genotyping