Sputum Eosinophilia
In addition to blood, eosinophils are also present in sputum of a patient of asthma. Eosinophilia in sputum (>20% of cells) may exist even when blood eosinophilia is absent. It is occasionally associated with Charcot-Leyden crystals in the specimen (thin, colourless, pointed structures of 20-40 mm length). Sputum eosinophil is usually present in symptomic asthma, but in contrast to the blood count, the number of cells in sputum correlates poorly with asthma severity.

Serum IgE
IgE antibody is an antibody that one time protected primitive people against many worms and parasitic diseases. Through the process of evolution this IgE antibody has become a harmful antibody, as it now overreacts to everyday common substance in our environment. gE antibody is an antibody that one time protected primitive people against many worms and parasitic diseases. Through the process of evolution this IgE antibody has become a harmful antibody, as it now overreacts to everyday common substance in our environment. 

This is both bad and good news . Bad new for the asthmatics who have inherited the tendency to make a lot of IgE antibodies. These may develop an allergic condition such as asthma or hay fever or a food or drug reaction. IgE Blood test measures the amount of allergic or IgE antibody in a persons serum or body. The  high IgE level indicates that allergies may be playing important role in asthma. This test is very helpful in predicting if infants or young children with asthma will ever develop allergies, as the IgE level may be elevated years before child develops obvious sign of asthma or hay fever. The presence of asthma is very closely related to serum IgE or allergic antibody level.

Recent data from a longitudinal study by Dr. Malcolm Sears of health ad development of 562 children in New Zealand disclosed that boys have higher prevalence of asthma than girls, and the prevalence of diagnosed asthma was closely related to the serum IgE level. No asthma was found in children with IgE levels less than thirty two units, whereas  more than one third of those with elevated IgE levels had asthma, and 25 percent of asymptomatic childern were shown  to have hyper reactive airway diseases when challenged by inhaling with an asthma-stimulating chemical such as methacholine. In other words, The  higher the IgE level, the greater the likelihood the boys and girls in the study had asthma. Sears' study concluded that even wheeze free children with an elevated IgE level may have hyper responsive airway closely linked to allergic tendencies.
 
The serum IgE level is a rough measure of the degree and number of allergies, the highest levels being found in patients with both asthma, rhinitis and eczema. Serum IgE may be within normal limits if an asthma/rhinitis patient has not been exposed to his allergens for months, and it must be emphasized that a normal IgE level does not exclude allergy.

Chest X-ray
A chest X-ray should be obtained in every patient. Primarily to exclude diseases other than asthma. The radiological appearance of the lungs in asthma. The radiological appearance of the lungs in asthma is usually normal. When asthma symptoms are persistent and when there is a rapid and serious deterioration,  a chest X-ray is essential for the diagnosis of complications such as atelectasis, pheumothorax, mediastinal or subcutaneous emphysema.

Other Examinations
ECG is a routine in patients with chest symptoms. A sweat test and determination of alpha, antitrypsin are relevent when asthma is complicated by bronchitis/emphysema. Determination of serum potassium is important, as theophylline, neta agonists, corticosteriods and diuretics (often given for steroid side effects), all reduce the serum level.

When your medical history, physical examination and laboratory tests suggest that allergy is playing a significant role in your asthma, skin prick test is usually indicated. In skin prick test, aqueous extracts (liquid dose) of potential allergens are injected into the skin. After 10-15 minutes, a weal or swelling appears at the site of the prick. Positive allergens are those injections where the swelling is more in comparison to saline injections. Sometimes, an anomalous situation arises when the skin prick test is positive, but the patient does not have any problem with that allergen in real life. Therefore, an allergen is considered important in the induction of the disease, only when it causes both skin-positive reaction and induction of allergic disease. At present there are three types of skin tests as mentioned below:       

• Prick or puncture test.
• Scratch test.
• Intradermal test.

b) Blood Test
It is possible to detect allergies with blood test known as RAST, PRIST and FAST tests. In these tests sample of blood is processed through an analyzer to see if the blood contains allergic IgE antibodies to certain allergens. These tests are very helpful when a doctor cannot perform skin test because of a skin eruption or a patient's fear of needle or when there is a chance of inducing an allergic reaction with skin test. Allergy blood test has three major disadvantages:

• They are not quite accurate as skin test.
• They are very expensive.
• Results are not available until two or three weeks after the test.

Summary
In symptom-free individuals, a diagnosis of asthma can be confirmed by a positive exercise or metacholine inhalation test. In symptomatic patients, asthma can be differentiated from bronchitis by the presence of eosinophilia in blood (and sputum), by the response to bronchodilators and steroids, and by a marked diurnal symptom variation. The blood eosinophil level is a measure of asthma severity, and increased serum IgE is an indicator of allergy. 
 
All the skin and allergy blood tests should be properly interpreted by an allergy specialist and correlated with your clinical history, positive test may not mean that you have the symptoms in response to test substance at the time of testing, as the skin test may be positive years before symptom begin and remain positive long after allergy symptoms.