Laboratory Studies
A few select laboratory studies may be performed, as indicated by features of the history or physical findings. Serologic tests may include the following:
- Iron studies
- Thyroid function tests[11]
- Rapid plasma reagin (RPR) and Venereal Disease Research Laboratory (VDRL) tests
- Antinuclear antibody (ANA) tests
Serum and urine amino acid levels may be determined.
If tinea capitis is a concern in the differential diagnosis, microscopic examination for fungal elements and culture for fungi may be performed.[12]
Other Tests
Phototrichography, trichoscanning, trichoscopy, and reflectance confocal microscopy may be used to evaluate hair loss from anagen effluvium.[13]
Procedures
Anagen effluvium can be distinguished from telogen effluvium by means of the pull test. To perform this test, firmly grasping 40 hairs between the thumb and forefinger and slowly pull on them to remove them, causing only mild discomfort to the patient. Then, a trichogram is used to quantify the ratio of terminal anagen hairs to telogen hairs. Anagen and telogen hairs can often be identified with the naked eye, but any doubts can be resolved by means of light microscopy. Anagen hairs have long indented roots covered with intact inner and outer root sheaths, and they are fully pigmented. Telogen hairs have short, club-shaped roots. They lack root sheaths and show depigmentation of the proximal part of the shaft. Fewer than 4-6 telogen hairs are typically present. A greater number of telogen hairs indicates a shift toward the telogen phase and suggests a probable diagnosis of telogen effluvium.
An alternative to is perform a gentle pull test or examine hairs removed by combing. The presence of tapered fractures is diagnostic of anagen effluvium.
Anagen effluvium can be distinguished from other forms of alopecia on the basis of the histologic changes on horizontal sections. A 4-mm punch biopsy sample of the scalp contains 25-50 follicles for inspection. Less than 15% of the follicles are normally in the telogen phase. A normal anagen-to-telogen ratio in a patient with hair loss is characteristic of anagen effluvium. A finding of greater than 15% of follicles in the telogen phase indicates a significant shift toward telogen in most individuals. This finding suggests telogen effluvium. The follicles should show no signs of inflammation, dystrophic changes of the inner sheath, or traction. These features permit the distinction of anagen effluvium from alopecia areata, androgenetic alopecia, and traction alopecia.
Histologic Findings
Anagen hairs have long, indented roots covered with intact inner and outer root sheaths. These hairs are fully pigmented. Telogen hairs have short, club-shaped roots. These hairs lack root sheaths and show depigmentation of the proximal parts of the shaft.
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van Beek N, Bodo E, Kromminga A, et al. Thyroid hormones directly alter human hair follicle functions: anagen prolongation and stimulation of both hair matrix keratinocyte proliferation and hair pigmentation. J Clin Endocrinol Metab. Nov 2008;93(11):4381-8. [Medline].
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