Global Journal of Transfusion Medicine

: 2020  |  Volume : 5  |  Issue : 2  |  Page : 212--214

White particulate matter – A mini review

Tanuja Pangtey, Roshan Chaudhary 
 Department of Blood Bank, Government Medical College, Haldwani, Uttarakhand, India

Correspondence Address:
Tanuja Pangtey
Department of Blood Bank, Government Medical College, Haldwani, Uttarakhand


White particulate matter has been an enigmatic entity inside blood bags. Frequent encounter with this uncommon phenomenon is described world over as a sporadic report or small series. Over the years, as its incidence keeps increasing so is the need to understand this strange entity that may provide valuable insights into the fascinating world of blood physiology and storage. An attempt to comprehend this strange phenomenon has been made in this brief review based on the literature available on this subject.

How to cite this article:
Pangtey T, Chaudhary R. White particulate matter – A mini review.Glob J Transfus Med 2020;5:212-214

How to cite this URL:
Pangtey T, Chaudhary R. White particulate matter – A mini review. Glob J Transfus Med [serial online] 2020 [cited 2021 Jun 25 ];5:212-214
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Full Text


White particulate matter (WPM) is a term given to microaggregates within blood units that are whitish and visible to the naked eye [Figure 1]. The number and size of these striking structures may vary.[1] The identification of WPM warrants careful observation of blood units and these may be missed when smaller in size. These are considered normal phenomena of blood storage and their formation is not believed to depend on donor characteristics.[2]

 Pathogenesis of White Particulate Matter

The actual pathogenesis of WPM is still unclear. WPM is believed to be composed of normal blood elements such as platelets, white blood cells (WBCs), cellular debris, and fibrin.[3] No external matter (like plastic particle) or organism has been associated with these formations.[3],[4] Cellular fragments and granules are also found in microscopic observation within the WPM.[4] Mostly, they are described to report in red cell units and not in whole blood units [Table 1].[5]{Figure 1}{Table 1}

Some of the factors described to be associated with their formation are as follows:

  1. Adhesiveness – Increased adhesiveness of platelet and WBCs compounded by increased stickiness on storage and cold temperature[3]
  2. High G forces – More frequent if higher “g” forces used in component preparation[3]
  3. Hard spin – WPM is commonly encountered in red cell units that undergo hard spin without platelet separation[4]
  4. Heavy centrifugation – WPM is more likely to form in component prepared by heavy centrifugation compared to the lighter method[5]
  5. Rate of flow – The rate of flow of blood unit with platelet is slower than platelet-poor red cell units. This favors microaggregation[6]
  6. High pressure – Stored whole blood undergoes high pressure through filters to increase storage time and might lead to compact aggregation due to increased platelet and WBC adhesiveness[7]
  7. Citrate-phosphate-dextrose-adenine (CPDA-1) in bag – Many reports of WPM have been found in units with CPDA-1. Random presence of WPM in whole blood units was found in 12 out of 356 units stored in a bag with citrate-phosphate-dextrose.[8] CPDA-1 is widely used in blood bags and impurity in this chemical compound may be a factor for macroaggregate formation.[9] The longer the blood is stored higher the concentration of acid phosphate in the blood, thus accelerating the formation of WPM when coupled with cellular breakdown products[10]
  8. Miscellaneous – Favorable factors in WPM formation are lipemia, increased platelet count, and hard spin during component preparation.[4],[10] High cholesterol was fund to associate with WPM, but triglyceride level had no apparent association.[5]


Buffy coat removal and leukofiltration may decrease the chances of their formation.[1] Removal of platelets and leukoreduction helps check the formation of WPM.[3],[4],[11]

Standard filters on normal use following proper instructions and microfilters usage for high-risk cases is advocated to be used as standard practice in this regard.[12]

 Further Investigations

Researchers advocate detailed investigation such as culture of contaminated blood unit and quarantine of the affected units.[12]

 What is to Be Done to Detect White Particulate Matter?

Every blood bank should have its own standard operating protocols regarding checking the blood before issuing the units. Many centers advocate and practice strict visualization of blood units before issuing apart from necessary paperwork. As per guidelines, the blood bag is kept with the labeled side down on a flat surface for 10 min undisturbed before visual inspection for any particles.[4],[12],[13] These may be small dots to big steaks that do not dissolve on shaking and may disintegrate on rubbing only to reappear again. WPM may also be found in tubings.[14]

 What Happens When This Blood Unit is Transfused?

Published articles believe that its inadvertent transfusion should not pose risk, but the issuance and transfusion should be avoided.[4],[12],[13] Potential adverse event (AE) and WPM association have not been conclusively given by authorities.[13] Quarantine of such units is advocated till compatibility and relevant investigation conclude suitability to transfuse these units.[12],[13],[14],[15] An observation by multiorganizational task force to assess increase AEs related to particulate matter and the effect of postleukofiltration on the particulate matter found no difference on AE in patients transfused with particulate matter laden blood. The authors, however, cautioned and concluded that results did not mean that there is no AE and the final evidence requires further research.[16]

 Types of White Particulate Matter

Enhanced visualization is advocated and the WPM has been divided into four types:[17]

  • Type 1 matter – consist of 20–5000 small WPM per unit
  • Type 2 matter – consist of 2–50 large WPM per unit
  • Type 3 matter – consist of atypical bubbles
  • Type 4 matter – consist of yellow/white oil slick.

 Is White Particulate Matter Found at Places Other Than Blood Bag?

A white thrombus type of matter, resembling as WPM with the composition of platelet and thrombin aggregation was noticed adhering in the lumen of dialysis blood tubings of many chronic dialysis patients. No previous report of WPM associated with hemodialysis treatment has been reported. Patient-specific and tubing-specific factors were supposed to cause this phenomenon warranting further studies.[18] One more case of recurrent white thrombi formation inside hemodialysis tubings of a young male with no pro-thrombotic risk factor is reported. The thrombus consisted of platelet aggregates and episodes improved on increased heparin dose.[19]

 Current Status and Future Trends

There are, however, no universal guidelines for issuing and transfusion of WPM containing units. Long-term studies to see the effect of WPM on recipient safety and AEs are required for better policy formation.


WPM is an uncommon but important phenomenon that is sporadically reported in the literature. Vigilant observation is crucial to report and record these unusual events. The knowledge of this phenomenon shall help to anticipate and identify these properly. While these particles are still enigmatic, collaborative studies are warranted to comprehend them fully.

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Conflicts of interest

There are no conflicts of interest.


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