diff --git a/fhir_utils/fhir/merge.py b/fhir_utils/fhir/merge.py
index 1206142..5f05547 100644
--- a/fhir_utils/fhir/merge.py
+++ b/fhir_utils/fhir/merge.py
@@ -17,10 +17,10 @@ def compare_resources(old_resource, new_resource):
     else:
         raise TypeError("Resource must be a dataclass or an instance of one")
 
-def merge_element(old_element, new_element, mode = "coalesce", coalesce_priority = "old"):
+def merge_element(old_element, new_element, mode = "coalesce", coalesce_priority = "old", unique_check = False, unique_key ="" ):
     """
     Merge two elements based on the specified mode.
-
+    
     Args:
         old_element (any): The original element to be merged.
         new_element (any): The new element to merge with the original.
@@ -28,7 +28,9 @@ def merge_element(old_element, new_element, mode = "coalesce", coalesce_priority
             Possible values: "replace", "union", "coalesce".
         coalesce_priority (str, optional): The priority for coalesce mode.
             Defaults to "old". Possible values: "old", "new".
-
+        unique_check (bool, optional): Flag to indicate whether to perform unique check in union mode. Defaults to False.
+        unique_key (str, optional): The key to use for unique check in union mode. Defaults to "".
+    
     Returns:
         any: The merged element based on the specified mode.
     """
@@ -36,7 +38,22 @@ def merge_element(old_element, new_element, mode = "coalesce", coalesce_priority
         case "replace":
             return new_element
         case "union":
-            return [old_element, new_element]
+            if unique_check == False:
+                return sum([old_element, new_element],[]) # flatten nested list
+            elif unique_check == True:
+                flat_list = sum([old_element, new_element],[])
+                unique_list = []
+                unique_keys = []
+                for e in flat_list:
+                    if type(e) is dict:
+                        if not e[unique_key] in unique_keys:
+                            unique_keys.append(e[unique_key])
+                            unique_list.append(e)
+                    else:
+                        raise TypeError("Old and New element both must be a list of dictionaries")
+                return unique_list     
+            else:
+                raise ValueError("Unique_check value must be boolean")      
         case "coalesce":
             if coalesce_priority == "old":
                 return old_element if old_element != "" else new_element