Alopecia, or hair loss, is a widespread concern. While conditions like pattern baldness have clear visual signs, sudden or excessive hair shedding often stems from systemic problems. The hair growth cycle is closely tied to the body’s overall internal environment. To accurately diagnose and create an effective treatment plan, medical professionals must look beyond the scalp and use objective measurements. Blood tests are a fundamental diagnostic tool, helping to uncover the physiological causes of hair changes.
Why Blood Tests are Essential for Diagnosis
Blood work provides a window into internal biochemistry that a visual examination cannot offer. Hair loss is often a late-stage symptom, developing internally for months before noticeable thinning or shedding occurs. Testing helps determine if hair changes manifest an underlying medical condition, such as an autoimmune disorder or chronic inflammation. This data distinguishes hair loss caused by genetic factors from that caused by a treatable systemic imbalance. Identifying a specific deficiency or hormonal issue allows treatment to be precisely targeted at the root cause.
Key Nutritional and Systemic Markers
Nutritional deficiencies are a common driver of hair shedding that blood tests can identify. Iron is needed to produce hemoglobin, which delivers oxygen to hair follicle cells to support growth. A serum ferritin test measures the body’s stored iron reserves. Levels below 40 to 50 micrograms per liter are often associated with increased shedding, even if full anemia is not present. Vitamin D (25-hydroxy vitamin D level) is also linked to hair follicle function, playing a role in initiating the anagen (growth) phase. Low levels are frequently observed in individuals experiencing telogen effluvium, a temporary form of diffuse hair loss.
A Complete Blood Count (CBC) provides a general health overview by measuring components like red blood cells, white blood cells, and platelets. The CBC helps identify anemia, which is often caused by iron deficiency and contributes to hair loss. Changes in white blood cell counts can also point toward an infection or an underlying inflammatory process impacting hair health.
Hormonal Imbalances and Related Testing
Hormone function is central to regulating the hair growth cycle. A comprehensive thyroid panel is routinely ordered, including Thyroid-Stimulating Hormone (TSH), free T3, and free T4. Both hypothyroidism (underactive thyroid) and hyperthyroidism (overactive thyroid) can disrupt the cycle, leading to diffuse hair thinning.
Androgen testing focuses on hormones that cause pattern baldness (androgenetic alopecia) in both sexes. These tests typically measure total and free testosterone, as well as Dehydroepiandrosterone Sulfate (DHEA-S). Elevated levels of these androgens, particularly in women, can lead to the miniaturization of hair follicles, resulting in finer, shorter hairs.
In women, a sex hormone imbalance can signal conditions like Polycystic Ovary Syndrome (PCOS), a common cause of hair thinning. Other related tests may include Prolactin or Sex Hormone Binding Globulin (SHBG), which affects hormone availability in the bloodstream. Identifying these specific hormonal patterns helps determine appropriate treatments, such as anti-androgen medications.
Preparation and The Testing Process
Accurate results require proper preparation before the blood draw. For certain hormone and metabolic panels, a healthcare provider may request eight to twelve hours of fasting. This requirement is due to the effect food intake can have on glucose, cholesterol, and other markers.
Patients must inform the provider about all medications and supplements being taken. Biotin supplements, in particular, can interfere with lab assays, potentially leading to falsely high or low results for hormones and thyroid markers. Patients are often advised to stop taking biotin for at least 72 hours before the sample is collected.
For premenopausal women, the timing of the blood draw may be specified to a certain point in the menstrual cycle, such as days two to five, to capture relevant hormone levels. After the blood is drawn, the sample is sent to a lab, and results are typically available within a few days to a week. The healthcare provider then uses these results to develop a targeted intervention plan.