Lungs

Aspergillosis precipitin is a laboratory test to detect antibodies in the blood resulting from exposure to the fungus nullAspergillus.

Aspergillus immunodiffusion test; Test for precipitating antibodies

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

The sample is sent to a laboratory where it is examined for precipitin bands that form when Aspergillus antibodies are present.

There is no special preparation.

When the needle is inserted to draw blood, you may feel moderate pain, or only a prick or stinging sensation. Afterward, there may be some throbbing.

Your doctor may order this test if blood work revealed that you have signs of a fungal infection.

See:

• Aspergillosis
• Allergic bronchopulmonary aspergillosis
• Invasive pulmonary aspergillosis

The normal test result is negative for Aspergillusantibodies.

A positive result means antibodies to the fungus have been detected. This usually means you have been exposed to the fungus at some point.

However, false-positive results are possible. For example, invasive aspergillosis often does not produce a positive result, even though Aspergillus is present.

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

Stevens DA. Aspergillosis. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier;2007:chap 360.

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Surfactant reduces surface tension, so that the alveoli in the lungs are able to expand. It is essentially a biological detergent.

Surfactant reduces surface tension. Without surfactant, the wet surfaces of the alveoli in your lungs would stick together and your lungs would not be able to expand - so, you would not be able to breath. The alveoli are the tiny sacs in your lungs where oxygen is captured from inhaled air and absorbed into your bloodstream. They are very small and are have moist surfaces. Wet surfaces stick together due to surface tension, which is caused by the attraction that water has for itself. To demonstrate how strong surface tension is, take two small glass panes, wet them slightly and press them together until there is no air between them. Now try to pull them apart. It's extremely difficult (you usually have to slide them apart because they will not separate otherwise). However, if you mix dish detergent in the water first, it will be much easier to pull them apart, because the detergent is a surfactant - a substance which combines with water and by doing so reduces the surface tension of the water.

About three to four weeks before birth, you lungs begin to produce surfactant. When you are born and take your first breath, you have to open the fluid-filled alveoli to allow air in. Without surfactant, this would be nearly impossible, which is which very premature infants have so much difficulty breathing. These very early preemies are given surfactant (either artificial or derived from calf lungs) down a tube going to their lungs, to help their alveoli open and allow air entry.

Some medical conditions cause loss of surfactant. In pulmonary edema, fluid from the blood invades and floods the alveoli. Among other problems, this causes dilution and washout of the surfactant, so that alveoli are more likely to collapse. Inflammation of the lungs also causes reduced surfactant production, so again the alveoli collapse due to increased surfaced tension. In cystic fibrosis, excess mucus production displaces the surfactant (and mucus has an even higher surface tension than water). Patients with CF are given extra surfactant to make up for this loss and to provide enough surfactant that it can act on the mucus as well as the normal alveolar fluid.