Reagent composition and kit

A reagent composition for use as a first reagent composition in a method of quantifying a small dense LDL cholesterol (sdLDL-C) in a sample, the method including

• causing the first reagent composition to react to the sample, and
• after the causing the first reagent composition to react to the sample, causing a second reagent composition for quantifying the sdL DL-C to react to the sample thereby quantifying cholesterol in a remaining lipoprotein,
• the reagent composition comprising a nonionic surfactant and having cholesterol esterase activity, cholesterol oxidase activity, and sphingomyelinase activity, wherein:
• a contact angle between the reagent composition and a polyethylene terephthalate (PET) base material, which is measured by the following method 1, is equal to or more than 63.0° and equal to or less than 67.0°,
• (method 1)
• (1) the PET base material:
• PET (amorphous polyester) resin plate, transparent, thickness of2 mm,
• (2) a pre-treatment:
• a surface of an unused PET base material is wiped with a 70% ethanol aqueous solution, and a measurement is performed within 5 minutes after the wiping,
• (3) a measurement method and conditions:
• a liquid droplet method, a θ/2 method, a temperature:
• 15° C. to 25° C., a syringe:
• Teflon-coated 18G, a dropwise addition method, a dropwise addition amount:
• 2 μL, a measurement 1 second after the dropwise addition, and
• (4) a calculation of the contact angle:
• the measurement is performed 5 times, and an average value of the 5 times is obtained.