What Is McCoy’s 5A Medium? A Clear Guide

McCoy’s 5A is a versatile, nutrient-rich medium that supports an unusually wide range of primary cells and established cell lines. Originally developed by Thomas McCoy, its modified form (McCoy’s 5A Modified Medium) is a standard choice for many cancer cell lines and demanding primary cultures. This guide explains what McCoy’s 5A is, what is in it, and which cells it suits.

What is McCoy’s 5A?

McCoy’s 5A is a chemically balanced basal medium known for its broad support of different cell types. It was developed for the culture of primary explants and later modified to improve its performance, giving the widely used McCoy’s 5A Modified Medium. Like other basal media, it supplies salts, amino acids, vitamins, and glucose, and it is completed with serum and glutamine before use.

What is in McCoy’s 5A?

A typical McCoy’s 5A formulation contains a broad set of inorganic salts, essential and non-essential amino acids, a rich vitamin profile, glucose, and a bicarbonate buffer with phenol red as a pH indicator. Because it uses a bicarbonate buffer, McCoy’s 5A needs a CO2 incubator (usually 5%) to hold the correct pH.

What is McCoy’s 5A used for?

McCoy’s 5A suits a wide variety of cells, including:

• Colon cancer lines such as HT-29 and HCT-116, for which it is a commonly recommended medium
• Primary cultures, including some difficult explants
• Lymphocytes and a range of other established lines

Its flexibility makes it a useful default when a protocol calls for it or when a cell line grows well across several media.

How to supplement and use McCoy’s 5A

Before use, McCoy’s 5A is completed with serum (commonly 10% FBS) and L-glutamine or a stable glutamine dipeptide. Keep it in a CO2 incubator, store it refrigerated and protected from light, warm it gently before use, and keep the same lot across an experiment for consistency.