This test focuses on the cause of the bleeding disorder as a means of distinguishing it from the various types of oculocutaneous and ocular albinism.

Using an Electron Microscope (described below) it is possible to directly observe whether dense granules are present or absent in blood platelets.  In the case of HPS, dense granules are either completely absent or present in very low numbers.

The sample of platelets must be unstained, not preserved \ encapsulated, or coated in any way, and must not be cut.  This is known as the ‘whole mount’ procedure.

Unfortunately EM is not easily accessed in the UK for diagnostic purposes through the National Health Service (NHS) except through Comprehensive Care Centres in the larger teaching hospitals such as Great Ormond Street Children’s Hospital (GOSH).  

The following pictures (electron-micrographs) clearly show the difference between normal and HPS platelets.  On the left the normal platelets have black spots that are the dense granules.  On the right the HPS platelets have no black spots and lack dense granules.  Normal platelets resemble choc chip cookies but HPS platelets look like plain butter cookies.

What is a Electron Microscope (EM)

An electron microscope is an ‘imaging’ device that can magnify an object typically from 50 thousand up to one million times. There are a number of types and, with some types, it is even possible to produce an image depicting the individual atoms of a substance.  Whilst they are called ‘microscopes’ they are unlike a standard light microscope found in a school classroom.  Instead of light they use a high energy beam of electricity (electrons) to produce an image that can be seen on a computer monitor or a screen at the base of the machine.  Skill is needed to interpret some of the images.  The images shown on this page (above) clearly show the difference between platelets that do and do not have dense granules in them.  Pictures like these are called ‘electron micrographs'.

Picture of a Transmission Electron Microscope.

Electron micrograph of normal platelets with dense granules showing as black spots   Picture of choc chip cookie to illustrate dense granules in normal platelets.       Electron micrograph of HPS platelets with no dense granules so no black spots or choc chips.   Picture of a plain butter cookie with no choc chips like a HPS platelet lacking dense granules.

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 Electron Microscopy (EM) for Hermansky-Pudlak Syndrome