diff --git a/backend/tests/fixtures/co_medicaid_837p.txt b/backend/tests/fixtures/co_medicaid_837p.txt
new file mode 100644
index 0000000..54def3f
--- /dev/null
+++ b/backend/tests/fixtures/co_medicaid_837p.txt
@@ -0,0 +1,60 @@
+ISA*00*          *00*          *ZZ*11525703       *ZZ*COMEDASSISTPROG*260617*1937*^*00501*991102984*1*P*:~
+GS*HC*11525703*COMEDASSISTPROG*20260617*193715*991102984*X*005010X222A1~
+ST*837*991102984*005010X222A1~
+BHT*0019*00*co-fixture-001*20260617*193715*CH~
+NM1*41*2*Dzinesco*****46*11525703~
+PER*IC*Tester*EM*tester@example.com~
+NM1*40*2*COLORADO MEDICAL ASSISTANCE PROGRAM*****46*COMEDASSISTPROG~
+HL*1**20*1~
+PRV*BI*PXC*251E00000X~
+NM1*85*2*TOC, Inc.*****XX*1881068062~
+N3*1100 East Main St*Suite A~
+N4*Montrose*CO*814014063~
+REF*EI*721587149~
+HL*2*1*22*0~
+SBR*P*18*******MC~
+NM1*IL*1*Balliache*Marianela****MI*P060946~
+N3*1811 PAVILION DR APT 303~
+N4*Montrose*CO*814016072~
+DMG*D8*19590223*F~
+NM1*PR*2*COHCPF*****PI*SKCO0~
+CLM*t991102984o1c1d*85.40***12:B:1*Y*A*Y*Y~
+REF*G1*3173~
+HI*ABK:R69~
+LX*1~
+SV1*HC:T1019:U2*42.70*UN*6.00***1~
+DTP*472*D8*20260602~
+REF*6R*t991102984v769804d~
+LX*2~
+SV1*HC:T1019:U2*42.70*UN*6.00***1~
+DTP*472*D8*20260603~
+REF*6R*t991102984v770058d~
+HL*3*1*22*0~
+SBR*P*18*******MC~
+NM1*IL*1*Barella*Victoria****MI*H582447~
+N3*1900 Kellie DR~
+N4*Montrose*CO*814019524~
+DMG*D8*19570727*F~
+NM1*PR*2*COHCPF*****PI*SKCO0~
+CLM*t991102984o1c2d*155.76***12:B:1*Y*A*Y*Y~
+REF*G1*3173~
+HI*ABK:R69~
+LX*1~
+SV1*HC:S5130:U2*38.94*UN*6.00***1~
+DTP*472*D8*20260602~
+REF*6R*t991102984v769805d~
+LX*2~
+SV1*HC:S5130:U2*38.94*UN*6.00***1~
+DTP*472*D8*20260603~
+REF*6R*t991102984v770059d~
+LX*3~
+SV1*HC:S5130:U2*38.94*UN*6.00***1~
+DTP*472*D8*20260604~
+REF*6R*t991102984v770308d~
+LX*4~
+SV1*HC:S5130:U2*38.94*UN*6.00***1~
+DTP*472*D8*20260605~
+REF*6R*t991102984v770668d~
+SE*44*991102984~
+GE*1*991102984~
+IEA*1*991102984~
\ No newline at end of file
diff --git a/backend/tests/test_co_medicaid_fixture.py b/backend/tests/test_co_medicaid_fixture.py
new file mode 100644
index 0000000..e15e49d
--- /dev/null
+++ b/backend/tests/test_co_medicaid_fixture.py
@@ -0,0 +1,40 @@
+from pathlib import Path
+
+from cyclone.parsers.parse_837 import parse
+from cyclone.parsers.payer import PayerConfig
+
+
+FIXTURE = Path(__file__).parent / "fixtures" / "co_medicaid_837p.txt"
+
+
+def test_co_fixture_two_claims_pass():
+    result = parse(FIXTURE.read_text(), PayerConfig.co_medicaid())
+    assert result.summary.total_claims == 2
+    assert result.summary.passed == 2
+    assert result.summary.failed == 0
+
+
+def test_first_claim_has_two_service_lines():
+    result = parse(FIXTURE.read_text(), PayerConfig.co_medicaid())
+    c1 = result.claims[0]
+    assert c1.claim_id == "t991102984o1c1d"
+    assert len(c1.service_lines) == 2
+    assert c1.service_lines[0].procedure.code == "T1019"
+    assert c1.service_lines[0].procedure.modifiers == ["U2"]
+    assert c1.service_lines[1].service_date is not None
+
+
+def test_second_claim_has_four_service_lines():
+    result = parse(FIXTURE.read_text(), PayerConfig.co_medicaid())
+    c2 = result.claims[1]
+    assert c2.claim_id == "t991102984o1c2d"
+    assert len(c2.service_lines) == 4
+
+
+def test_subscriber_payer_reused_across_claims():
+    """Both claims share the same billing provider; payers are recorded on each claim."""
+    result = parse(FIXTURE.read_text(), PayerConfig.co_medicaid())
+    assert result.claims[0].billing_provider.npi == "1881068062"
+    assert result.claims[1].billing_provider.npi == "1881068062"
+    assert result.claims[0].payer.id == "SKCO0"
+    assert result.claims[1].payer.id == "SKCO0"