What is the first step to determining a patient's weight-for-age percentile?

To determine a patient's weight-for-age percentile, the first step involves plotting the age of the patient on the x-axis of a growth chart. This process is essential because growth charts are designed to provide a comparative analysis based on specific age intervals. The age serves as the baseline for understanding where the patient's weight falls within the context of the typical growth patterns for their age group.

By plotting the age first, healthcare providers can accurately assess the relationship between the patient's age and weight, which is vital for determining whether they are within a healthy range, underweight, overweight, or obese. This enables practitioners to provide appropriate interventions and advice.

Other options, such as measuring height or plotting weight, are subsequent steps. While consulting a growth chart is crucial, it is not a distinct step in the plotting process but rather a resource that uses the age data to interpret weight in context. Therefore, establishing the patient's age as the initial reference point is essential for accurately determining their weight-for-age percentile.