fix: align Trisomy 21 BMI upper bound

rcpchgrowth/tests/test_reference_vectors_and_boundaries.py

@@ -130,7 +130,14 @@ def test_every_reference_includes_its_lower_boundary_and_rejects_below_it(
         ),
         (CDC, 2, 1.9999, BMI, MALE, "BMI below 2 years"),
         (CDC, 3, 3.0001, HEAD_CIRCUMFERENCE, MALE, "head circumference above 3 years"),
-        (TRISOMY_21, 18.82, 18.8201, BMI, MALE, "BMI reference data"),
+        (
+            TRISOMY_21,
+            18.92,
+            math.nextafter(18.92, math.inf),
+            BMI,
+            MALE,
+            "BMI reference data",
+        ),
         (TRISOMY_21, 18, 18.0001, HEAD_CIRCUMFERENCE, MALE, "head circumference"),
         (TRISOMY_21_AAP, 0.083333333, 0.0829, HEIGHT, MALE, "below 1 month"),
         (TRISOMY_21_AAP, 2, 1.9999, BMI, MALE, "below 2 years"),

rcpchgrowth/tests/test_trisomy_21_reference_boundaries.py

@@ -0,0 +1,34 @@
+import math
+
+import pytest
+
+from rcpchgrowth.constants import BMI, FEMALE, MALE, TRISOMY_21
+from rcpchgrowth.global_functions import sds_for_measurement
+
+
+@pytest.mark.parametrize("sex", [MALE, FEMALE])
+@pytest.mark.parametrize("age", [18.83, 18.92])
+def test_trisomy_21_bmi_accepts_final_source_ages(sex, age):
+    result = sds_for_measurement(
+        reference=TRISOMY_21,
+        age=age,
+        measurement_method=BMI,
+        observation_value=25.0,
+        sex=sex,
+    )
+
+    assert math.isfinite(result)
+
+
+@pytest.mark.parametrize("sex", [MALE, FEMALE])
+def test_trisomy_21_bmi_rejects_age_after_last_source_age(sex):
+    with pytest.raises(
+        LookupError, match=r"Trisomy BMI reference data does not exist > 18\.92 y\."
+    ):
+        sds_for_measurement(
+            reference=TRISOMY_21,
+            age=math.nextafter(18.92, math.inf),
+            measurement_method=BMI,
+            observation_value=25.0,
+            sex=sex,
+        )

rcpchgrowth/trisomy_21.py

@@ -51,8 +51,8 @@ def reference_data_absent(
     if age > TWENTY_YEARS: # upper threshold of trisomy_21 data
         return True, "Trisomy 21 reference data does not exist over the age of 20y."
 
-    elif measurement_method == BMI and age > 18.82:
-        return True, f"Trisomy BMI reference data does not exist > 18.82 y."
+    elif measurement_method == BMI and age > 18.92:
+        return True, "Trisomy BMI reference data does not exist > 18.92 y."
 
     elif measurement_method == HEAD_CIRCUMFERENCE:
         if age > EIGHTEEN_YEARS:
@@ -80,4 +80,4 @@ def select_reference_data_for_trisomy_21(measurement_method:str, sex:str):
         return_value = trisomy_21_lms_array_for_measurement_and_sex(measurement_method=measurement_method, sex=sex, age=0.0)
     except:
         raise LookupError(f"No data for {measurement_method} in the {sex} Trisomy 21 dataset.")
-    return return_value
+    return return_value