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Test Code HIPABU or LAB3528 Heparin PF4 Platelet Antibody - Unfractionated Heparin

Important Note

The Heparin PF4 Platelet Antibody assay is performed on patients being administered Unfractionated Heparin (UFH) or Low Molecular Weight Heparin (LMWH. The confirmatory test, Serotonin Release Assay, is also non-specific to the anticoagulant being administered.

Profile Information

Test ID

Reporting Name

Available Separately?

Always Performed?

HIPABU

Heparin PF4 Platelet Antibody, UFH

N

Y

SRAU

Serotonin Release Assay

N

N

Specimen Requirements

Specimen Type:

Whole Blood

Container Type:

Blue top: 2.7 mL or 1.8 mL

Optimal Collection Volume:
  • 2.7 mL in solid blue top tube or 1.8 mL in clear blue top tube.  The correct fill volume is indicated by the etched line on the tube.
  • Click here to view the specimen collection guide for blue top (citrate) tubes.

Collection Instructions:
  1. Gently invert 5 to 10 times to mix blood.
  2. If collected through a blood collection set (butterfly), a discard tube must first be drawn to eliminate dead space from tubing.  

Specimen Transport Temperature:
  • Room temperature for up to 4 hours. If testing is delayed, separate plasma and freeze (see outpatient collection instructions below).
  • Specimens cannot be refrigerated

Processing Instructions:
  1. Centrifuge sample within 4 hours of collection. Platelet-poor plasma must be obtained per laboratory procedure.
  2. If testing will be delayed >4 hours from collection, aliquot plasma into a separate vial and freeze immediately.

Outpatient collections

  1. Spin down the sample, remove plasma, and spin plasma again to obtain platelet-poor plasma.
  2. Separate the platelet-poor plasma into a screw-top vial.
  3. Freeze plasma immediately.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Specimen Stability

Specimen Type

Temperature

Time

Whole blood

Room Temperature

4 hours

Platelet Poor Plasma

Room Temperature

4 hours

Platelet Poor Plasma

Frozen at - 20 C

18 months

Specimen Rejection Criteria

  • Tube underfilled
  • Refrigerated specimen
  • Clotted specimen
  • Specimen not processed within four hours of collection

Useful For

Evaluation of possible immune-mediated type II heparin-induced thrombocytopenia (HIT-II), which should be suspected for the following patients:

  • Patients not previously exposed to heparin the development of absolute thrombocytopenia or a decrease in platelet count of ≥50% from baseline or postoperative peak with the onset of thrombocytopenia beginning approximately 5 to 10 days after initiation of heparin. This may or may not be associated with new or progressive thrombosis in patients treated with heparin.
  • In addition to the above findings, patients previously exposed to heparin (especially within the preceding 100 days), the onset of thrombocytopenia could occur within 24 to 48 hours after re-exposure to heparin.
  • In patients with prior suspected or documented heparin-induced thrombocytopenia (HIT), with or without thrombosis, assay for the presence of human platelet factor 4 (H/PF4) antibody may be useful in the assessment of the risk of recurrence of HIT with additional exposure to heparin; however, prospective data are limited.

Methodology

The HIT-Ab (PF4) assay is a qualitative, fully automated, latex-enhanced immunoassay for detecting anti-platelet factor 4/heparin (PF4/H) antibodies performed on the ACL Top 500 coagulation analyzer.

Reference Ranges

Negative

 

Note on positive results - A reflex order will be placed to send a new sample to our reference lab for the coagulant-appropriate serotonin release assay.

Interpretive

A positive result for anti-Platelet Factor 4/heparin (PF4/H) antibodies suggests the presence of antibodies implicated in the pathogenesis of immune-mediated heparin induced thrombocytopenia (HIT).   This assay is intended only as a qualitative screening test.

When a result is positive in a screening test, it DOES NOT CONFIRM the diagnosis of HIT. Some patients may have naturally occurring antibodies to PF4.  To form a diagnosis, this screening test result should be used in conjunction with clinical context, and resources including the 4T score and the 2013 American Society of Hematology guidelines.

 

Positive screening results should also be confirmed with a functional assay.

 

4T Score for the Probability of Heparin-Induced Thrombocytopenia

Category

2 points

1 point

0 points

Thrombocytopenia

Platelet count fall > 50% AND nadir ≥ 20 x 109 L-1

Platelet count fall between 30-50% AND nadir 10-19 x 109 L-1

Platelet count fall < 30% OR nadir < 10 x 109 L-1

Timing of platelet count fall from heparin initiation

Clear onset between days 5-10 of first exposure OR within one day of re-exposure after prior heparin use within 30 days

Consistent with days 5-10 fall, but not clear (e.g., missing data, platelets rise and fall) OR onset after day 10 OR within one day of re-exposure after prior heparin use within 30-100 days

Platelet count fall < 4 days AND no heparin exposure last 100 days

Thrombosis or other sequelae

New confirmed thrombosis OR necrosis at heparin injection site OR acute systemic reaction after IV heparin bolus

Progressive or recurrent thrombosis OR non-necrotizing (erythematous) skin lesions or suspected thrombosis (not proven)

None

Other causes for Thrombocytopenia 1,2

None apparent

Possible

Definite

1. Chronic thrombocytopenia; infection; DIC; intra-arterial device (e.g., IABP, VAD, ECMO); Cardiopulmonary bypass within 4 days

2. New non-heparin medication. PCNs, cephs, sulfonamides, GPIIb/IIIa Inhibitors, linezolid, SMX-TMP, vancomycin, VPA, phenytoin, digoxin have highest incidence. Mean onset 7-14d, often nadir < 20 x 109 L-1. Recovery begins within 1-2d after discontinuation.

 

Day(s) Performed

Monday through Friday - 24/7

Expected TAT

Same day to 3 days

Performing Laboratory

Bronson Laboratory, Coagulation - Kalamazoo

Sample Retention Time

24 hours

CPT Code

86022

LOINC Code

34701-3

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