NLM classification scheme

QS Human anatomy
QT Physiology
QU Biochemistry
QV Pharmacology
QW Microbiology and immunology
QX Parasitology
QY Clinical pathology
QZ Pathology
W Medical profession (including education)
WA Public health and health administration
WB Medicine general
WC Infectious diseases, AIDS
WD Deficiency and metabolic diseases, allergy, aerospace medicine
WE Musculoskeletal system
WF Respiratory system
WG Cardiovascular system
WH Haemic and lymphatic systems
WI Gastrointestinal system
WJ Urogenital system
WK Endocrine system
WL Nervous system
WM Psychiatry
WN Radiology and medical imaging
WO Surgery
WP Gynaecology
WQ Obstetrics
WR Dermatology
WS Paediatrics
WT Geriatrics and chronic disease
WU Dentistry and oral surgery
WV Otorhinolaryngology
WW Ophthalmology
WX Hospitals and other health facilities
WY Nursing
WZ History of medicine