diff --git a/sru/onbsru.py b/sru/onbsru.py
index 335b38bdbfe43366ee90f56f413d2c59fb9d7325..8ec7bf5f17dd34c18fd1c18857f2f216bfb65097 100644
--- a/sru/onbsru.py
+++ b/sru/onbsru.py
@@ -14,37 +14,42 @@ class OnbRecordRetriever(almasru.RecordRetriever):
                  xml_format: str = 'marcxml'):
         super().__init__(subdomain, inst_code, xml_format)
 
+        self.namespaces = {
+            'srw': 'http://www.loc.gov/zing/srw/',
+            'marc': 'http://www.loc.gov/MARC21/slim'
+        }
+
     # Create alias for querying AC-numbers
     def by_ac_num(self, ac_num: str):
         return self.by_marc_009(ac_num)
 
-    def get_pids_for_ac(self, ac_num: str) -> list:
+    def get_pids(self, xml: Element) -> list:
         """
         Extract all PIDs from XML based on MARC 856 4 2.
         PIDs are identifiers migrated from a legacy system.
 
-        :param ac_num: ID used in Austrian Library Network
+        :param xml: MARC xml as xml.etree.ElementTree Element
         :return: List of identifiers.
         """
 
-        namespaces = {
-            'srw': 'http://www.loc.gov/zing/srw/',
-            'marc': 'http://www.loc.gov/MARC21/slim'
-        }
-
-        marc_xml = self.by_ac_num(ac_num)
-        datafields = marc_xml.findall("marc:datafield", namespaces)
+        datafields = xml.findall("marc:datafield", self.namespaces)
 
         pids = []
 
         for datafield in datafields:
             if datafield.attrib == {'tag': '856', 'ind1': '4', 'ind2': '2'}:
-                marc_856_u = datafield.find("marc:subfield[@code='u']", namespaces)
+
+                marc_856_u = self._get_subfield(datafield, 'u')
                 marc_856_url = marc_856_u.text
-                marc_856_x = datafield.find("marc:subfield[@code='x']", namespaces)
+
+                marc_856_x = self._get_subfield(datafield, 'x')
                 marc_856_note = marc_856_x.text
+
                 if 'ONB-DTL' in marc_856_note:
                     pids.append(self.pid_re.findall(marc_856_url)[0])
-                marc_856_url = None
 
         return pids
+
+    def _get_subfield(self, element, subfield):
+        xpath = "marc:subfield[@code='"+subfield+"']"
+        return element.find(xpath, self.namespaces)
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