When should 'Plt' (platelet count) versus 'Plt F' (flagged platelet count) be reported to the healthcare provider in Sysmex hematology results?

Reporting Platelet Counts on Sysmex Hematology Analyzers

Report PLT-F (fluorescence channel) to providers when available, as it provides superior accuracy compared to standard PLT-I (impedance channel), particularly in thrombocytopenic and abnormal samples where clinical decisions about transfusion thresholds are critical.

Understanding the Two Measurement Methods

PLT-I (Impedance Method)

• Uses electrical impedance to count particles based on size 1, 2
• Cost-effective and standard on most analyzers 3
• Susceptible to interference from small red blood cells, red cell fragments (schistocytes), white blood cell fragments, and other non-platelet particles 1, 3, 2
• Can produce falsely elevated counts in anemic and thrombocytopenic samples 3, 4

PLT-F (Fluorescence Method)

• Uses fluorescent dye that specifically stains intraplatelet organelles (particularly those labeled with anti-Grp75) while only faintly staining cell membranes 1
• Clearly distinguishes platelets from fragmented erythrocytes through specific staining properties 1
• All strongly stained cells are confirmed to be platelet-specific (CD41+ and CD61+) 1
• Provides superior accuracy in abnormal samples including those from burn injury, acute leukemia, and severe aplastic anemia 5, 2

When PLT-F is Essential

Critical clinical scenarios where PLT-F should be reported:

• Thrombocytopenic samples (PLT <50 × 10⁹/L): PLT-F reduces falsely elevated results by nearly fivefold compared to PLT-I 3
• Anemic patients: PLT-F shows excellent correlation (0.991-0.999) with reference methods across all types of anemia 3
• Patients with hemolysis: Ghost cells and spiny cells from hemolysis interfere with PLT-I but not PLT-F 5
• Hematologic malignancies: White blood cell fragments in acute leukemia samples interfere with PLT-I 2
• Burn injury patients: Red cell fragments cause spurious PLT-I elevations 2

Clinical Decision Thresholds

Understanding when platelet counts matter for bleeding risk:

• 50 × 10⁹/L threshold: Significant for immediate post-procedural bleeding risk (OR = 6.6 for procedures like polypectomy; OR = 8.79 for percutaneous ablation) 6
• Transfusion decisions: Generally recommended to maintain >50 × 10⁹/L in ongoing bleeding 7
• Higher-risk procedures: Target >100 × 10⁹/L for traumatic brain injury or critical conditions 7

Practical Reporting Algorithm

Follow this decision tree:

1. If PLT-F is available on your analyzer → Report PLT-F as the primary platelet count 1, 3, 2

2. If only PLT-I is available:

   • Report PLT-I for normal samples (no flags, normal histogram)
   • Flag for manual review if: thrombocytopenia, anemia, hemolysis, hematologic malignancy, or any PLT flags present 5, 2
   • Perform microscopic platelet estimation using platelet-to-RBC ratio in flagged samples 5

3. If PLT-I and PLT-F are discordant:

   • Prioritize PLT-F as the accurate count 3, 2, 4
   • PLT-I typically overestimates in these cases 3, 4

Common Pitfalls to Avoid

• Do not assume normal histograms guarantee accuracy: Spurious high platelet counts can occur without PLT flags or abnormal histograms in special hematologic patients 5
• Do not rely solely on PLT-I in thrombocytopenic samples: At counts ≤2.0 × 10⁹/L, PLT-F shows better reproducibility than PLT-I 4
• Do not ignore discordant results at transfusion thresholds: In 41 discordant samples near transfusion cutoffs, PLT-I (optical equivalent) showed higher counts than PLT-F in all but one case, potentially delaying necessary transfusions 4

Reproducibility Considerations

• PLT-F exceeds desirable precision criteria (7.6%) in 60% of severely thrombocytopenic samples (≤2.0 × 10⁹/L) 4
• PLT-I optical methods exceed precision criteria in only 10% of the same samples 4
• For critical decisions in severe thrombocytopenia, consider repeat testing or manual verification 5, 4