Introduction

No tests are necessary for most patients with acne. Tests may be requested to look for infection, to investigate the cause of the disease, or to monitor treatment.

Tests for micro-organisms

Although bacteria, especially Cutibacterium acnes (formerly known as Propionibacterium acnes), are involved in the development of acne, they are a normal part of the skin flora and can be detected in people with or without acne lesions.

Occasionally it is wise to obtain a swab and/or scraping from an acne spot, or acne-like pustule, for microbiological examination and culture. This is because acne can resemble infections, including:

• Pyogenic bacterial folliculitis due to Staphylococcus aureus
• Gram negative folliculitis
• Malassezia folliculitis
• Tinea faciei due to a dermatophyte fungus such as Trichophyton rubrum or Microsporum canis.

Hormone tests

Some women may be advised to have blood tests to measure hormone levels. The reasons include:

• Possibility of pregnancy, which would influence what treatment was appropriate
• Signs suggesting hyperandrogenism (high levels of male sex hormones), which could be due to conditions such as polycystic ovaries or congenital adrenal hyperplasia
• Signs suggesting excessive prolactin
• Signs suggesting Cushing syndrome.

These hormone tests are best taken between 8:00 and 10:00 am during the first half of the menstrual cycle. They may include:

• Testosterone
• Sex hormone binding globulin (SHBG)
• Free androgen index (FAI)
• Dehydroepiandrosterone sulfate (DHEAS)
• 17-hydroxyprogesterone
• Synacthen test of adrenal stimulation by adrenocorticotrophic hormone (ACTH)
• Luteinising hormone (LH) and follicular stimulating hormone (FSH)
• Prolactin
• Cortisol
• Dexamethasone suppression test.

Imaging

A pelvic ultrasound scan is usually very good at excluding ovarian cysts and tumours on the ovary and adrenal gland. X-rays, computed tomography (CT) scans or magnetic resonance imaging (MRI) may also be arranged if there is suspicion of tumour.

Tests to monitor treatment

Blood tests may be performed to monitor the safety of treatment:

• Full blood count (especially if the patient is unwell)
• Liver function in those on antibiotics or isotretinoin
• Fasting lipids (cholesterol and triglyceride) in those on isotretinoin
• Beta human chorionic gonadotrophin or HCG (pregnancy test) in those on isotretinoin.