dark viscous phelgm

Does dark phlegm always indicate a sinus infection?  Does it mean something different if it's the color of dried blood, as opposed to a green color?

[National Jewish]

The best way to identify a sinus infection is with a sinus CT scan, although sinus x-rays are a decent alternative.  A sinus CT scan will also identify if any of the openings that drain your sinuses are blocked.

Sinusitis is an inflammation of the mucous membranes that line the sinus cavities.  Inflammation of the sinuses could be due to an allergy, an infection, or ongoing exposure to an irritant, such as pollution or smoke.  The most common cause of sinusitis is an infection, especially when the phlegm is green.  Sinus infections can be difficult to treat since they respond slowly.  When any of the openings that drain your sinuses are blocked it will take longer to clear a sinus infection.  If a viral infection is the cause it