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Blood Products - Platelets

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Dosage of Platelets

  • One bag of platelets/m2, on average, produces an increment of 40 x 109/l.
  • The usual platelet dose is 10-15 ml/kg up to 1 bag. If a child is > 0.5 m2 then round up to avoid wastage.
  • If there are concerns about fluid volume, discuss volume reduction with Blood Bank.

Indications for Platelet Support

  • Bone marrow failure from leukaemia or chemotherapy/radiotherapy:
    • Patient is well - transfuse if < 10 x 109/l
    • Patient is unwell:
      - febrile (temp >38°C) transfuse if < 20 x 109/l
      - spontaneous bruising and petechiae transfuse if < 30 x 109/l
  • DIC: give BD platelets, transfusing if < 50 x 109/l.
  • Lumbar puncture2: keep count > 30 x 109/l except for diagnostic LP where platelets should be > 50 x 109/l to minimise the risk of a traumatic tap or if LP is known to have been technically difficult or not done under GA where platelets should be > 50 x 109/l.
  • Surgical procedures (the final decision rests with the surgeon) - keep count > 50 x 109/l:
    • epidural anaesthesia
    • insertion of central venous catheter
    • transbronchial biopsy
    • liver biopsy
    • dental extractions
    • laparotomy
  • Surgery at critical sites - keep platelets > 100 x 109/L during and for 48 hours after the procedure:
    • neurosurgery
    • eye surgery
  • It should not be assumed that the platelet count will rise just because a platelet transfusion is given - a preoperative platelet count should be done to ensure that the above thresholds are reached.
  • It is crucial to check the platelet count frequently after surgery to ensure the count is maintained.
  • For neurosurgery patients, ensure platelets > 30 x 109/L for 2 months after the procedure.
  • Retinoblastoma patients receiving chemotherapy and SALT (sequential aggressive local therapy e.g. cryotherapy) - keep platelets > 30 x 109/L.
  • Adolescent female with menorrhagia - keep platelets > 30 x 109/L.

Rhesus (D) Negative Recipients

Although platelets do not carry Rh antigens, the infusion may have small numbers of donor red blood cells that could sensitise Rh negative individuals. In immunocompromised patients the rate of Rh sensitisation is low. Rh (D) negative children should preferably receive Rh (D) negative platelets. If only Rh (D) positive platelets are available, then anti-D immunoglobulin should be given:

  • To both male and female children.
  • Give the IV anti-D Ig product.
  • Give immediately after the platelet infusion.
  • Repeat every 4 weeks if further Rh positive platelets are given. It may be necessary to repeat more frequently (3-weekly) if substantial Rh positive platelet transfusion is required.

Platelet Refractoriness

A poor platelet response is defined as a corrected count increment (CCI) of < 5000 microL.

CCI = Platelet increment (109/L) x BSA (m2)
-----------------------------------------------------
           1011 platelets transfused

A typical bag of platelets contains 2.4 x 1011 platelets.

Platelet refractoriness should only be diagnosed when poor increments occur after at least 2 ABO compatible, fresh (< 72 hours old) platelet transfusions.

Make sure the poor increments are not due to:

  • sepsis
  • active haemorrhage
  • splenomegaly
  • consumptive coagulopathy
  • post-BMT thrombotic thrombocytopenic purpura
  • hepatic veno-occlusive disease
  • ITP

Once all the above provisos are excluded, the most likely diagnosis is alloimmunisation.

90% of alloimmunised patients will have detectable HLA antibodies (the remainder have antibodies to ABO or membrane glycoproteins). Platelet cross-matching techniques can identify suitable donors. Alternatively patients with HLA antibodies can be managed with platelet transfusions that are HLA -A and B matched i.e., class I matched.

If the patient is severely lymphocytopenic so that HLA class cannot be detected, platelet cross-matching techniques can identify suitable donors. These techniques should also be employed for the 40% of patients who do not respond to class I HLA matched platelet transfusions. Alloimmune platelet refractoriness is not responsive to steroids, IVIG or splenectomy.

Ordering HLA Matched Platelets

  • Discuss with NZ Blood Service consultant.
  • It takes time to arrange HLA matched platelets. Therefore, try to detect early refractoriness by checking increments.
  • HLA matched platelets should be infused within 24 hours of collection. Irradiation is required.

References

  1. Guidelines on the use of platelet transfusions. British committee for standards in haematology. British Journal of Haematology, 2003, 122, 10-23
  2. Howard SC et al. Safety of lumbar puncture for children with acute lymphoblastic leukaemia and thrombocytopenia. JAMA 2000;284(17):2222-2224.
  3. NZBS transfusion medicine handbook, 2008

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Document Control

  • Date last published: 20 April 2016
  • Document type: Clinical Guideline
  • Services responsible: National Child Cancer Network
  • Owner: Siobhan Cross
  • Review frequency: 2 years