The CEAP classification was developed by the AVF in 1994 and later revised in 2004.

The classification is based on clinical signs of venous disease (C), etiology (E), anatomy (A), and the underlying pathophysiology (P).

• C - Clinical class includes the full spectrum of venous disorders, from no signs of visible venous disease (C₀) to telangiectasia or reticular veins (C₁), varicose veins (C₂), edema (C₃), skin changes, such as pigmentation or eczema (C_4a) or lipodermatosclerosis or atrophie blanche (C_4b), and healed (C₅) or active (C₆) ulcer. The presence or absence of symptoms is also recorded as S (symptomatic) or A (asymptomatic).
• E - Etiology can be congenital (E_c), primary (E_p), or secondary (E_s).
• A - The anatomic classification separates superficial venous disease (A_s) from involvement of the perforators (A_p) or deep veins (A_d). Failure to identify an anatomic location is also coded (A_n).
• P - Pathophysiology of the disease can be reflux (P_r), obstruction (P_o), or both. Failure to identify venous pathophysiology is also noted (P_n).

Table II includes the full CEAP classification, and Table III lists the venous segments that can be involved in the disease.

The basic CEAP classification is a simplified version, suitable and easy for office use, and does not have the details of the comprehensive CEAP classification, which functions more as a research tool. As discussed in more detail by Meissner et al, for a patient with primary, symptomatic varicose veins and full saphenous and perforator incompetence (anatomic segments 2, 3, and 18 in Table III) with a small healed venous ulcer and skin pigmentation, the comprehensive CEAP classification would be C_2,4a,5,SE_pA_s,p,P_r2,3,18. Using the basic CEAP, the same patient would be classified as C_5,SE_pA_s,pP_r. In the basic CEAP classification, only the highest score is used to denote the clinical class and only the main anatomic groups (s, p, and d) are noted.

The revised format of the classification includes two elements in addition to the C-E-A-P findings: the date of the examination and the level of the diagnostic evaluation:

• Level 1: History, physical examination, Doppler examination (handheld)
• Level 2: Noninvasive–duplex scan, plethysmography Level 3: Invasive or complex evaluation–contrast venography, venous pressure measurements, IVUS, CT venography, MR venography

The accuracy of the diagnosis increases with the addition of imaging and invasive testing. Recording the date and method used to confirm the clinical impression can be added in parentheses after the CEAP recording as follows:

• Full form: C_{2,4a,5, S} E_p A_{s, p} P_r2,3,18 (Level 2, Feb 8, 2010)
• Basic form: C_{5, S} E_pA_{s p}P_r (Level 2; Feb 8, 2010)

The main purpose of using the CEAP classification in patients with CVD is to distinguish primary venous disease from congenital varicosity and, most importantly, from secondary, postthrombotic venous insufficiency. Evaluation and treatment of the three conditions are distinctly different.