What is a hit lab panel called?

HIT Laboratory Panel Testing

The laboratory panel for diagnosing heparin-induced thrombocytopenia (HIT) consists of an immunoassay followed by a functional assay when the immunoassay is positive. 1

Diagnostic Algorithm for HIT

Step 1: Clinical Probability Assessment

• Calculate the 4Ts score to determine pre-test probability of HIT 1
• The 4Ts score evaluates:
  • Thrombocytopenia (degree of platelet count fall)
  • Timing of platelet count fall
  • Thrombosis or other sequelae
  • Other causes of thrombocytopenia 1

Step 2: Laboratory Testing Based on 4Ts Score

• For low-probability 4Ts score (≤3):

  • Laboratory testing for HIT is generally not recommended 1
  • HIT is unlikely and heparin can be continued 1

• For intermediate/high-probability 4Ts score (>4):

  • Discontinue heparin and start non-heparin anticoagulant 1
  • Obtain immunoassay as first-line laboratory test 1

Step 3: Immunoassay Testing

• Immunoassay detects antibodies against PF4/heparin complexes 1
• Common immunoassay types:
  • Enzyme-linked immunoassay (ELISA) - preferred with low threshold 1
  • Other commercially available antigen assays 1

Step 4: Functional Assay (if immunoassay positive)

• Functional assays detect the platelet-activating properties of HIT antibodies 1
• Types of functional assays:
  • Serotonin release assay (SRA)
  • Heparin-induced platelet activation (HIPA)
  • Other washed platelet assays 1
• Functional assays should use washed platelets for increased reliability 1

Interpretation of Results

• HIT is confirmed when both:

  • Immunoassay is positive
  • Functional assay is positive 1

• For high-probability 4Ts score with strongly positive immunoassay (e.g., ELISA >2.0 OD units):

  • Functional assay may not be necessary 1

• For positive functional assay results:

  • Procoagulant platelet formation should be observed with low-dose heparin
  • This effect should be markedly reduced or abolished with high-dose heparin 1

Phases of HIT and Laboratory Findings

• Suspected HIT: Clinical suspicion but pending laboratory confirmation 1
• Acute HIT: Decreased platelet count with positive immunoassay and functional assay 1
• Subacute HIT A: Normal platelet count, positive functional assay, positive immunoassay 1
• Subacute HIT B: Normal platelet count, negative functional assay, positive immunoassay 1
• Remote HIT: Normal platelet count, negative functional assay, negative immunoassay 1

Important Considerations

• Immunoassays are widely available with relatively rapid turnaround time 1
• Functional assays may need to be sent to reference laboratories, increasing cost and wait time 1
• False positives can occur with immunoassays detecting clinically insignificant antibodies 1
• In some centers, functional assays may be performed in tandem with immunoassays for quality assurance 1