The "Positive" Pull Test: What does it mean?

A Positive Pull Test: Many Diagnoses

A "pull test" is a test for excessive shedding. To perform the pull test, the clinician gently wraps his or her thumb and index finger around approximately 60 hairs and pulls gently upwards. If more than 3 hairs are removed, one should consider it a positive pull test. (the old cut off used to be 6 hairs but recent studies have suggested that number is not appropriate for most).

Does a positive pull test mean telogen effluvium?

It's a common error to assume that a positive pull test equates to a telogen effluvium. While the pull test is often used to give the clinician some sense if whether a telogen effluvium might be present this is not the only hair loss condition that gives a telogen effluvium.  The reality is that many conditions give a positive pull test including androgenetic alopecia, alopecia areata and scarring alopecia. In other words a positive pull test is not definitive for any given diagnosis but certainly indicates that something is not quite right with how the patient is losing hair.

Let's take a closer look at these conditions 

1. Telogen Effluvium

Telogen effluvium (TE) is the prototypical hair shedding condition. Hair shedding in a TE occurs all over the scalp which means that the pull test is positive all over the scalp. Not everyone with a TE has a positive pull test as a variety of factors can influence this, including when the patient last washed their hair.  Typical causes of TE include stress, low iron, thyroid problems, medications, diets, and illness inside the body (systemic illness).

2. Androgenetic alopecia

Contrary to what many patients and clinicians think, increased hair shedding does occur in the early stages of androgenetic alopecia (male and female balding). Sometimes a pull test can be weakly positive in these areas. Performing a pull test is a bit trickier int these conditions simply because the findings are subtle. But if one performs a pull test in areas of androgenetic alopecia and compares the findings to areas where there is no androgenetic alopecia, one can appreciate that a few more hairs are frequently extracted from the are of androgenetic alopecia. 

3. Alopecia areata

Alopecia areata is an autoimmune condition that affects about 2 % of the world's population. It causes inflammation to accumulate deep under the scalp around hair follicles. This inflammation can trigger shedding. In the earliest stages, alopecia areata can closely mimic a telogen effluvium and not surprisingly a pull test is frequently positive. The hairs that are extracted in alopecia areata are a bit different than a true TE and include a mix of telogen hairs, broken hairs and so called 'dystrophic anagen hairs."

4. Scarring alopecia

Patients with scarring alopecia may also have a positive pull test. Lichen planopilaris, Idiopathic Pseudopelade of Brocq, Discoid Lupus Erythematosus can all trigger increased shedding. The pull test in these situations may reveal telogen hairs as in a telogen effluvium, but may frequently also reveal anagen hairs. In fact, the extraction of normal appearing anagen hairs is a pathognomic sign of a scarring alopecia. 

Reference

McDonald et al. Hair pull test: Evidence-based update and revision of guidelines. Journal of the American Academy of Dermatology 2017; 76: 472