diff --git a/pandas/_libs/missing.pxd b/pandas/_libs/missing.pxd
index e32518864db0a..854dcf2ec9775 100644
--- a/pandas/_libs/missing.pxd
+++ b/pandas/_libs/missing.pxd
@@ -7,7 +7,6 @@ from numpy cimport (
 cpdef bint is_matching_na(object left, object right, bint nan_matches_none=*)
 
 cpdef bint checknull(object val, bint inf_as_na=*)
-cpdef bint checknull_old(object val)
 cpdef ndarray[uint8_t] isnaobj(ndarray arr, bint inf_as_na=*)
 
 cdef bint is_null_datetime64(v)
diff --git a/pandas/_libs/missing.pyx b/pandas/_libs/missing.pyx
index 6146e8ea13f89..2d66a655ba075 100644
--- a/pandas/_libs/missing.pyx
+++ b/pandas/_libs/missing.pyx
@@ -135,10 +135,6 @@ cdef inline bint is_decimal_na(object val):
     return isinstance(val, cDecimal) and val != val
 
 
-cpdef bint checknull_old(object val):
-    return checknull(val, inf_as_na=True)
-
-
 @cython.wraparound(False)
 @cython.boundscheck(False)
 cpdef ndarray[uint8_t] isnaobj(ndarray arr, bint inf_as_na=False):
@@ -176,12 +172,6 @@ cpdef ndarray[uint8_t] isnaobj(ndarray arr, bint inf_as_na=False):
     return result.view(np.bool_)
 
 
-@cython.wraparound(False)
-@cython.boundscheck(False)
-def isnaobj_old(arr: ndarray) -> ndarray:
-    return isnaobj(arr, inf_as_na=True)
-
-
 @cython.wraparound(False)
 @cython.boundscheck(False)
 def isnaobj2d(arr: ndarray, inf_as_na: bool = False) -> ndarray:
@@ -221,12 +211,6 @@ def isnaobj2d(arr: ndarray, inf_as_na: bool = False) -> ndarray:
     return result.view(np.bool_)
 
 
-@cython.wraparound(False)
-@cython.boundscheck(False)
-def isnaobj2d_old(arr: ndarray) -> ndarray:
-    return isnaobj2d(arr, inf_as_na=True)
-
-
 def isposinf_scalar(val: object) -> bool:
     return util.is_float_object(val) and val == INF
 
diff --git a/pandas/core/dtypes/missing.py b/pandas/core/dtypes/missing.py
index 63b64dc504b52..d2733cddf8cee 100644
--- a/pandas/core/dtypes/missing.py
+++ b/pandas/core/dtypes/missing.py
@@ -158,10 +158,7 @@ def _isna(obj, inf_as_na: bool = False):
     boolean ndarray or boolean
     """
     if is_scalar(obj):
-        if inf_as_na:
-            return libmissing.checknull_old(obj)
-        else:
-            return libmissing.checknull(obj)
+        return libmissing.checknull(obj, inf_as_na=inf_as_na)
     elif isinstance(obj, ABCMultiIndex):
         raise NotImplementedError("isna is not defined for MultiIndex")
     elif isinstance(obj, type):
diff --git a/pandas/tests/dtypes/test_missing.py b/pandas/tests/dtypes/test_missing.py
index 55d0e5e73418e..e04df7e43838f 100644
--- a/pandas/tests/dtypes/test_missing.py
+++ b/pandas/tests/dtypes/test_missing.py
@@ -565,21 +565,19 @@ def test_na_value_for_dtype(dtype, na_value):
 
 
 class TestNAObj:
-
-    _1d_methods = ["isnaobj", "isnaobj_old"]
-    _2d_methods = ["isnaobj2d", "isnaobj2d_old"]
-
     def _check_behavior(self, arr, expected):
-        for method in TestNAObj._1d_methods:
-            result = getattr(libmissing, method)(arr)
-            tm.assert_numpy_array_equal(result, expected)
+        result = libmissing.isnaobj(arr)
+        tm.assert_numpy_array_equal(result, expected)
+        result = libmissing.isnaobj(arr, inf_as_na=True)
+        tm.assert_numpy_array_equal(result, expected)
 
         arr = np.atleast_2d(arr)
         expected = np.atleast_2d(expected)
 
-        for method in TestNAObj._2d_methods:
-            result = getattr(libmissing, method)(arr)
-            tm.assert_numpy_array_equal(result, expected)
+        result = libmissing.isnaobj2d(arr)
+        tm.assert_numpy_array_equal(result, expected)
+        result = libmissing.isnaobj2d(arr, inf_as_na=True)
+        tm.assert_numpy_array_equal(result, expected)
 
     def test_basic(self):
         arr = np.array([1, None, "foo", -5.1, NaT, np.nan])
@@ -676,16 +674,16 @@ def test_checknull(self, func):
 
     def test_checknull_old(self):
         for value in na_vals + sometimes_na_vals:
-            assert libmissing.checknull_old(value)
+            assert libmissing.checknull(value, inf_as_na=True)
 
         for value in inf_vals:
-            assert libmissing.checknull_old(value)
+            assert libmissing.checknull(value, inf_as_na=True)
 
         for value in int_na_vals:
-            assert not libmissing.checknull_old(value)
+            assert not libmissing.checknull(value, inf_as_na=True)
 
         for value in never_na_vals:
-            assert not libmissing.checknull_old(value)
+            assert not libmissing.checknull(value, inf_as_na=True)
 
     def test_is_null_datetimelike(self):
         for value in na_vals: