diff --git a/resources/home/dnanexus/generate_gcnv_bed/generate_gcnv_bed.py b/resources/home/dnanexus/generate_gcnv_bed/generate_gcnv_bed.py
index 81fe341..3e84eae 100644
--- a/resources/home/dnanexus/generate_gcnv_bed/generate_gcnv_bed.py
+++ b/resources/home/dnanexus/generate_gcnv_bed/generate_gcnv_bed.py
@@ -10,6 +10,7 @@
 
 import argparse
 from concurrent.futures import as_completed, ProcessPoolExecutor
+import numpy as np
 from os import cpu_count
 from pathlib import Path
 import subprocess
@@ -101,7 +102,12 @@ def read_single_copy_ratio_file(copy_ratio_file) -> Tuple[str, pd.DataFrame]:
             comment="@",
             header=0,
             names=["chr", "start", "end", sample_name],
-            dtype={"chr": str, "start": int, "end": int, sample_name: float},
+            dtype={
+                "chr": "category",
+                "start": np.uint32,
+                "end": np.uint32,
+                sample_name: float,
+            },
             float_precision="high",
         )
     except Exception as exc:
diff --git a/resources/home/dnanexus/generate_gcnv_bed/tests/test_generate_gcnv_bed.py b/resources/home/dnanexus/generate_gcnv_bed/tests/test_generate_gcnv_bed.py
index 35bec49..b4f7c39 100644
--- a/resources/home/dnanexus/generate_gcnv_bed/tests/test_generate_gcnv_bed.py
+++ b/resources/home/dnanexus/generate_gcnv_bed/tests/test_generate_gcnv_bed.py
@@ -6,6 +6,7 @@
 from glob import glob
 import gzip
 from math import sqrt
+import numpy as np
 import os
 from pathlib import Path
 from uuid import uuid4
@@ -89,6 +90,15 @@ def test_contents_correctly_parsed_into_dataframe(self):
             },
         )
 
+        expected_df = expected_df.astype(
+            {
+                "chr": "category",
+                "start": np.uint32,
+                "end": np.uint32,
+                "sample_1": float,
+            }
+        )
+
         _, parsed_df = read_single_copy_ratio_file(
             copy_ratio_file=self.sample_1_test_file
         )
@@ -181,6 +191,16 @@ def test_reading_all_files_to_dataframe_correct(self):
                 ],
             },
         )
+        expected_df = expected_df.astype(
+            {
+                "chr": "category",
+                "start": np.uint32,
+                "end": np.uint32,
+                "sample_1": float,
+                "sample_2": float,
+                "sample_3": float,
+            }
+        )
 
         self.assertTrue(copy_ratio_df.equals(expected_df))
 
@@ -383,9 +403,9 @@ def test_contents_correctly_written_to_file(self):
                 "mean_minus_std2",
             ],
             dtype={
-                "chr": str,
-                "start": int,
-                "end": int,
+                "chr": "category",
+                "start": np.uint32,
+                "end": np.uint32,
                 "sample_1": float,
                 "sample_2": float,
                 "sample_3": float,
@@ -482,9 +502,9 @@ def test_contents_correct_when_keep_all_samples_true(self):
                     "mean_minus_std2",
                 ],
                 dtype={
-                    "chr": str,
-                    "start": int,
-                    "end": int,
+                    "chr": "category",
+                    "start": np.uint32,
+                    "end": np.uint32,
                     "sample_1": float,
                     "sample_2": float,
                     "sample_3": float,
@@ -561,9 +581,9 @@ def test_contents_correct_when_keep_all_samples_false(self):
                     "sample_1",
                 ],
                 dtype={
-                    "chr": str,
-                    "start": int,
-                    "end": int,
+                    "chr": "category",
+                    "start": np.uint32,
+                    "end": np.uint32,
                     "sample_1": float,
                     "mean": float,
                     "mean_plus_std": float,