platelets |

PLATELETS

Shubham Yadav

Post graduate resident, department of medicine, LHMC

Introduction

Platelets are produced in bone marrow from megakaryocytes. Megakaryocytes are the large polyploidal, nucleated cell. Whereas platelets are – small in size, aneucleated, average number ~ 2 lakhs/microL. Half life is around 10 days. Approximately 100 billion platelets are produced each day and production can be increased upto > 10 times.

COLLECTION PROCESS

Platelet Concentrates can be collected from

WHOLE BLOOD – RDP

Whole blood is centrifuged ( soft spin ) to separate into RBC and PRP (satellite bag). PRP centrifuged at higher rates to sediment platelets. Plasma is removed into another satellite bag. Platelet pellets are resuspended in – 50mL residual plasma which is known as platelet concentrates.

Anticoagulants used can be CPD or CPDA.

Whole blood needs to be stored @ room temperature and has to be processed within 8 hrs.

APHERESIS – SDP

Produced with help of continuous flow devices. Centrifugal forces are applied to separate compartments as – PRP – Buffy coat(WBCs) and RBC. Desired fraction to be removed is pumped into bag and remaining reinfused back continuously.

Upto 3 therapeutic platelet doses obtained ( 6 times more than whole blood). Also there are fewer WBCs ( leukoreduced <10^6 )

300mL SDP should contain around – 3 x 10^11 platelets by AABB standards. ( vs 5 x 10^10 in Platelet Concentrates unit which is produced from wholw blood).

STORAGE

Platelets are stored @ room temp ( 20 – 24 C).

At 4 C – platelets undergo shape changes and lose their viability.

They are buffered by HCO3 which is present in plasma in which they are suspended.

PVC bags are impermeable to gases and have shelf life of 3 days.

New Plastic bags are more permeable and have shelf life of 7 days. However approved storage is of 5 days.

Platelets are gently agitated, stored in sufficient plasma to maintain pH above 6.2.

ADMINISTRATION

Platelets should be administered within 4 hrs after puncturing the bag using leukoreduction platelet filter. Dose – 1 unit/10kg. Assesment of recovery is done after 10min to 1 hr post transfusion. Maximal ideal recovery should be as – 1 apheresis PC : 40 x 10^9 platelets. However in practice only 50% recovery is seen. Acceptable recovery is around : 30% (12k-13K) or more.

CCI (CORRECTED COUNT INCREMENT)

Recovery varies with patient’s size and doses transfused

CCI = (posttransfusion count – pretransfusion count) × body surface area (m2) /number of platelets administered

The maximum achievable CCI is 25 × 10^9/L. Typically 12.5 10^9/L CCI is achieved in practice. Acceptable limit of CCI is : 7.5 x 10^9/L.

INDICATIONS

Indications of platelet transfusion are:

Actively Bleeding Patient

50k/microL in most bleeding situation incuding DIC

100k/microL if CNS bleed

also address – Fever, surgical defect, infection,

inflammation, coagulopathy

Prophylactic

threshold of 10k/microL – prevent spontaneous bleed.

febrile/septic – 20k-30k/microL

APL (have coexisting coagulopathy)- 30k-50k/microL

previous levels at which patient had episode of bleeding.

Preparation For Invasive Procedure

Most major surgery – 50k/microL

Neurosurgery – 100k/microL

Endoscopy: Therapeutic 50k/microL

Diagnostic (with low risk) 20k/microL

Bronchoscopy – 20k-30k/microL

CVC insertion – 20k/microL

Lumbar Puncture – 20k/microL: pt with hematological malignancy.

50k/microL: without

BMA or biopsy: 20k/microL.

COMPLICATIONS

Infectious – bacterial contamination or septic platelet transfusion reaction (SPTR) is more common as compared to the other components.

Transfusion reaction –

FNHTR (WBCs or by cytokines)

Anaphylactic – common, Ig E Ab to donor plasma proteins

TRALI: Antibodies against Neutrophils

TACO: rare

Post Transfusion Purpura (PTP)

Bibliography

1.Wintrobe’s Clinical Hematology, 14e John P. Greer, George M. Rodgers, Bertil Glader, Daniel A. Arber, Robert T. Means, Jr.; Alan F. List, Frederick R. Appelbaum, Angela Dispenzieri, Todd A. Fehnige