Diagnosing Hair Loss - Laboratory tests

Laboratory tests

Additional tests may sometimes be necessary to confirm the diagnosis. These may include:

Blood tests. This may be done to detect iron deficiency, thyroid disease, excessive androgen production, syphilis and discoid lupus erythematosus.

Microscopy. This allows the doctor to identify structural defects and fungal infections.

Culture. This is used to detect fungal infections. However, the result takes six weeks to return, limiting its usefulness.

Anagen-telogen ratio. In this test, between 20 and 30 hairs are carefully plucked to include their roots and examined under a microscope.

Anagen and telogen hairs can be identified and their number and the ratio of anagen to telogen hairs (A:T ratio) determined. Doctors regard 20% as the maximum proportion of hairs in telogen. Using this figure, the normal A:T ratio should be at least 80:20 (80% anagen:20% telogen) or 4: 1. It is reduced in telogen effluvium and in areas affected by male pattern baldness.

Hair density. This is done by shaving a small area of the scalp about four centimeters above the ear. The area is then stamped with a biopsy punch, an instrument of eight millimeter in diameter, giving a circle of 0.5 square centimeter in area. The number of hairs (not the follicle openings) within the circle is counted with the aid of a magnifying glass, and the number of hairs per square centimeter calculated. The normal number is 150 per square centimeter.

Length of hair growth. An area of the scalp is shaved and the length of hair measured a month later. The norm is 11.2 centimeter per month. The same area of the scalp used for measuring hair density can also be used. This test is also useful for reassuring the patient that hair is growing.

Scalp biopsy. This involves removing a piece of scalp tissue and examining it under a microscope. The area to be biopsied is first anaesthetized to numb the pain. It is useful for the diagnosis of many scalp and hair disorders. The discomfort is minimal and there is no risk of injuring underlying structures such as the skull bones or the brain.

Apart from examining and conducting tests, the doctor is also there to answer any queries that you may have; so make the best use of your time with him or her. Hair loss is a distressing condition and may cause a variety of psychological problems. The doctor can counsel and provide psychological support if this is required.

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