In medical and clinical research, **follow-up** refers to:

> **The ongoing observation and assessment of a patient or study participant over some time after an initial treatment, diagnosis, or intervention.**

---

### 🔍 **Purposes of Follow-Up**
- **Monitor disease progression or recurrence**  
  (e.g., tumor recurrence after surgery)
- **Evaluate treatment outcomes**  
  (e.g., functional recovery, complications)
- **Detect late-onset side effects**
- **Ensure adherence to therapy or rehabilitation**
- **Collect long-term data** for research or registries

---

### 📅 **Types of Follow-Up**
- **Short-term follow-up**: days to weeks  
  (e.g., postoperative wound healing)
- **Long-term follow-up**: months to years  
  (e.g., survival, relapse rates in cancer)

---

### 🧪 **In Research Studies**
Follow-up is crucial to:
- Assess **primary and secondary endpoints**
- Calculate **outcome measures** like survival rate, recurrence, or treatment efficacy
- Reduce **loss to follow-up**, which can introduce bias

---

### 🧾 Example in a Study
> "All patients were followed up every 6 months with MRI and endocrine tests for at least 5 years."

This means researchers kept evaluating the patients' status regularly to track outcomes and complications.