Refer to figure.
An ILS approcach is a 3D instrument approach since it provides both horizontal and vertical guidance. The minimum altitude at which a missed approach must be initiated if the required visual reference to continue the approach has not been established is the definition of Decision Altitude (DA) for a 3D instrument approach.

For ILSz approach RWY 03:

• DA = 273 ft
• DH = 200 ft

The missed approach point is located at 0.7 DME from NT (NT is the ILS with DME the procedure is based on, named Nantes) and it will be reached at a DA of 273 ft.

ICAO Doc 8168
Chapter 1 DEFINITIONS

Decision altitude (DA) or decision height (DH). A specified altitude or height in a 3D instrument approach operation at which a missed approach must be initiated if the required visual reference to continue the approach has not been established.

Note 1.— Decision altitude (DA) is referenced to mean sea level and decision height (DH) is referenced to the threshold elevation.

Question 103050 is similar but asks about the minimum height instead of the minimum altitude.