LABELLED WHITE BLOOD CELL SCANS and GALLIUM

There are three types:

1. WBC's labelled with Tc and HMPAO. This is preferred because the dose to the patient is 3mSv.

The way this is done is to take whole blood, spin it down, take off the white blood cells and baste them with Tc HMPAO. This takes 3 hours to do!

You will normally just see hot liver and spleen and faintly hot marrow, because this is where white cells hang out in the body. Images are typically taken once an hour, so the patient is sitting around the department for another 3 hours!
This is a problem if you are trying to see if there is a splenic or hepatic abscess. Then you need to look for cold spots.

However, after 3 hours of imaging, the actual Tc-HMPAO (not the white blood cells) is pooed out and so you see hot bowel.

You try to minimize this as a problem by having the patient fast the day before and take Golytely the night before. This means that there is no poo for the HMPAO to tack on to.

A classic situation to be aware of is when you have a bone scan that is hot but a white cell scan is cold. In this case, the likely situation is treated cellulitis. The differential is treated osteomyelitis. You can differentite the two by how hot the bone is. If it's hot, then it was OM because bone images take weeks to improve. Whereas, if it was cellulitis, then the bone will only be warm, and that's because the cellulitis will have led to increase blood flow to the entire area, and so more MDP will have been available to be taken up by the bone - therefore that bone will appear hotter.

2. Indium-labelled white blood cells. This is used for abdominal imaging because Indium is not pooed out.
The drawback is that you get 3x the radiation dose (3 x 3mSv is the mnemonic).

3. Leukoscan, which is a monoclonal antibody that is removed from protesting mice, having been developed in those mice by injecting them with human WBC's.

The alternative is GALLIUM.
The advantage is mainly for patients who might have an infected prosthesis. This is because the prosthesis will squish marrow and therefore you will have a hot WBC scan around the prosthesis. Therefore, you need to do a sulfur colloid marrow study to see if there is a similar appearance of hotness.
Whereas, gallium will not be hot unless there is an infection.
The disadvantage is that it gives a high radiation dose and one needs to wait several days after giving it before you can take pictures (and therefore are unsure for those days whether you have an infection or not)