Laboratory Studies
Laboratory studies are of little use in the diagnosis of telogen effluvium if there is clear history of an inciting event. Scalp biopsy is the most useful test to confirm the diagnosis, although this is seldom necessary if the history is characteristic and a gentle hair pull produces numerous telogen hairs. Telogen hairs are identified by a white bulb and the lack of a gelatinous hair sheath.
If a biopsy is performed, some authors advocate taking three 4-mm punch biopsy specimens, all imbedded horizontally. This method provides a generous sample for determining anagen-to-telogen and terminal-to-vellus ratios and leads to greater diagnostic accuracy. [28]
Chronic telogen effluvium may have a metabolic cause. Testing should be directed toward causes that are common and correctable. If any sign or symptom of hypothyroidism is present, a thyrotropin test is warranted. Iron deficiency is common in premenopausal women. Evaluation of CBC count, serum iron, iron saturation, and ferritin may be warranted. Note that CBC count results may be completely normal in women with mild iron deficiency and hair loss, particularly in women older than 40 years. Blood is more essential than hair, and the body will shed hair before red cell indices become microcytic. Also, note that ferritin behaves as an acute phase reactant. Inflammation can produce normal ferritin levels in an individual who is iron deficient. Although a low ferritin is proof of iron deficiency, a normal ferritin level does not exclude iron deficiency. Some experts in the field regard iron saturation as the most sensitive indicator of iron deficiency.
Occasionally, screening for renal and hepatic enzymes may detect a systemic cause of hair shedding. If syphilis is considered as a cause of hair loss, a rapid plasma reagin or Venereal Disease Research Laboratory test should be preformed.
Other Tests
If a patient is unwilling to undergo a scalp biopsy but would like confirmation of the diagnosis, serial hair collections may be obtained. This process can educate the patient in the normal hair cycle and can confirm the spontaneous resolution of the process.
The patient should be instructed to collect all hairs shed in a 24-hour period. The patient should not shampoo the hair during the day of collection. This process should be repeated every week or every other week, for a total of 3 or 4 collections.
Collections totaling 100 hairs or more in a given 24-hour period are indicative of ongoing telogen effluvium. If the collections are performed over several weeks while the telogen effluvium is resolving, the number of hairs collected each time should decrease. This finding can be very comforting to the patient.
An alternate method of hair collection has been proposed by Rebora et al. According to this method, the patient collects hair during shampooing and the physician both counts and measures the length of these hairs. This method has the advantage of being able to detect and differentiate between telogen effluvium and androgenetic alopecia, even when the 2 conditions occur in the same individual. [29] The disadvantage to this method is that it cannot be used in patients who have short hair (< 3 cm). Additionally, the counting and measuring procedure is very labor intensive, which limits its practicality in normal clinical practice.
Ross et al report on the successful use of videodermoscopy in the diagnosis of hair and scalp disorders. [30] The color-transition sign has been used to differentiate alopecia areata from telogen effluvium. [31]
Histologic Findings
Histologic findings in telogen effluvium are subtle and are most easily seen on transverse sections of a punch biopsy. The number and density of hair follicles is normal, but an increased percentage of the hair follicles are in telogen or catagen phase. If more than 25% of the follicles are in telogen phase, the diagnosis is confirmed. The percentage of telogen hairs generally should not be higher than 50%.
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Telogen effluvium secondary to hypothyroidism.
