Step-by-step diagnostic approach
Characteristic history and examination findings are usually sufficient to diagnose acne vulgaris.
Acne vulgaris classically begins as puberty commences, but the clinical course is highly variable. Women may note a fluctuating course centred on their menstrual cycles. Acne fulminans is a rare acne subtype that presents with variable systemic manifestations, including fever, arthralgias, myalgias, hepatosplenomegaly, and osteolytic bone lesions.
Certain drugs may induce acne, and a thorough drug history should be elicited.
Non-inflammatory acne manifests as whiteheads (closed comedones) and blackheads (open comedones). Inflammatory lesions begin as microcomedones but may develop into papules, pustules, nodules, or cysts. Both types of lesions are found in areas of dense sebaceous glands. View imageView image Acne may affect only the face, but the chest, back, and upper arms are often involved. Moderate-to-severe acne lesions may leave post-inflammatory hyperpigmentation and/or atrophic scars. View image Other individuals may form more hypertrophic scars at areas of prior involvement.  Severe nodulocystic acne View image presenting with fever, arthralgia, myalgia, hepatosplenomegaly, and osteolytic bone lesions suggests acne fulminans.
Routine endocrinological testing is not indicated for the majority of patients with acne. In patients with acne and evidence of hyperandrogenism, hormonal evaluation for free testosterone, dehydroepiandrostenedione sulphate (DHEA-S), luteinising hormone (LH), follicle stimulating hormone (FSH) is done. 
Routine microbiological testing is unnecessary in the evaluation and management of patients with acne. If lesions centred in the peri-oral and nasal areas are unresponsive to conventional acne treatments, bacterial culture and sensitivities to evaluate for gram-negative folliculitis are considered.