Final answer:
c) Amount of drug injected
In medical records, the 'Amount of drug injected' typically allows for only three digits, reflecting the standard measurement units and usual dosage sizes.
Step-by-step explanation:
The element that typically has room for only three digits in medical records is c) Amount of drug injected. Medical records often use standardized fields with a limited number of characters, and the field for the amount of drug injected is commonly restricted to three digits. This is because dosages for medications are often measured in standard units such as milligrams or milliliters, and for most medications, it is rare to exceed a three-digit amount.