From 0a58edc87a2615d3724c22a4571283de16d83151 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marc-Andr=C3=A9=20Bombeck?= <mbombeck@gmail.com>
Date: Sat, 26 Sep 2026 13:55:41 +0200
Subject: [PATCH] fix(fhir): code the mean glucose only when it is a
 continuous-stream mean

97507-8 is the mean of interstitial glucose in mass/volume. A spot-reading
mean is neither, so it now goes out text-only in the account's unit. A
continuous-stream mean keeps the code and is sent in mg/dL, the unit it is
computed in, whatever unit the account displays.
---
 .../glucose-clinical-observations.test.ts     | 49 +++++++++++++++++++
 src/lib/fhir/resources/glucose.ts             | 33 +++++++++----
 2 files changed, 72 insertions(+), 10 deletions(-)

diff --git a/src/lib/fhir/__tests__/glucose-clinical-observations.test.ts b/src/lib/fhir/__tests__/glucose-clinical-observations.test.ts
index 1274631e9..8562be554 100644
--- a/src/lib/fhir/__tests__/glucose-clinical-observations.test.ts
+++ b/src/lib/fhir/__tests__/glucose-clinical-observations.test.ts
@@ -131,6 +131,55 @@ describe("clinical glucose-panel FHIR Observations", () => {
     expect(tir!.valueQuantity?.value).toBeLessThanOrEqual(100);
   });
 
+  it("codes a continuous-stream mean as 97507-8 in mg/dL, even for a mmol/L account", () => {
+    const glucoseClinical = computeGlucoseClinicalMetrics(denseReadings(), {
+      now: FIXED_NOW,
+      windowDays: 90,
+    });
+    expect(glucoseClinical.isSpotEstimate).toBe(false);
+    const bundle = buildFhirDocumentBundle(
+      makeData({ glucoseClinical, glucoseUnit: "mmol/L" }),
+      { insuranceNumber: null },
+      FIXED_NOW,
+    );
+    const mean = observationsOf(bundle).find(
+      (o) => o.code.text === "Mean glucose",
+    );
+    expect(codeOf(mean!)).toBe(GLUCOSE_MEAN_LOINC);
+    expect(mean?.valueQuantity?.code).toBe("mg/dL");
+    expect(mean?.valueQuantity?.value).toBe(
+      Math.round(glucoseClinical.meanMgdl!),
+    );
+  });
+
+  it("sends a spot-reading mean text-only, in the account's unit", () => {
+    // Four readings a day: fingerstick cadence, not a continuous stream.
+    const sparse = Array.from({ length: 120 }, (_, i) => ({
+      measuredAt: new Date(FIXED_NOW.getTime() - i * 6 * 3_600_000),
+      mgdl: 100 + (i % 5) * 10,
+    }));
+    const glucoseClinical = computeGlucoseClinicalMetrics(sparse, {
+      now: FIXED_NOW,
+      windowDays: 90,
+    });
+    expect(glucoseClinical.isSpotEstimate).toBe(true);
+    expect(glucoseClinical.meanMgdl).not.toBeNull();
+    const bundle = buildFhirDocumentBundle(
+      makeData({ glucoseClinical, glucoseUnit: "mmol/L" }),
+      { insuranceNumber: null },
+      FIXED_NOW,
+    );
+    const mean = observationsOf(bundle).find(
+      (o) => o.code.text === "Mean glucose",
+    );
+    expect(mean).toBeDefined();
+    expect(mean?.code.coding).toBeUndefined();
+    expect(mean?.valueQuantity?.unit).toBe("mmol/L");
+    expect(observationsOf(bundle).map(codeOf)).not.toContain(
+      GLUCOSE_MEAN_LOINC,
+    );
+  });
+
   it("emits NO clinical glucose Observation when the panel has no readings (module off / no data)", () => {
     // Default makeData() has an empty (zero-reading) panel.
     const bundle = buildFhirDocumentBundle(
diff --git a/src/lib/fhir/resources/glucose.ts b/src/lib/fhir/resources/glucose.ts
index 0ec140729..5f5c3aaa2 100644
--- a/src/lib/fhir/resources/glucose.ts
+++ b/src/lib/fhir/resources/glucose.ts
@@ -143,16 +143,29 @@ export function glucoseClinicalObservations(
     });
   }
   if (clinical.meanMgdl !== null) {
-    push({
-      loinc: {
-        code: GLUCOSE_MEAN_LOINC,
-        display:
-          "Average glucose [Mass/volume] in Interstitial fluid during Reporting Period",
-      },
-      text: "Mean glucose",
-      value: convertGlucose(clinical.meanMgdl, glucoseUnit),
-      unit: glucoseUnit,
-    });
+    // 97507-8 is the mean of interstitial glucose in mass/volume. Only a
+    // continuous stream (not a spot estimate, by reading density) is
+    // interstitial, so only that mean carries the code, and it goes out in
+    // mg/dL: the canonical unit the mean is computed in, so no conversion is
+    // involved. A spot-reading mean stays text-only in the display unit.
+    if (clinical.isSpotEstimate) {
+      push({
+        text: "Mean glucose",
+        value: convertGlucose(clinical.meanMgdl, glucoseUnit),
+        unit: glucoseUnit,
+      });
+    } else {
+      push({
+        loinc: {
+          code: GLUCOSE_MEAN_LOINC,
+          display:
+            "Average glucose [Mass/volume] in Interstitial fluid during Reporting Period",
+        },
+        text: "Mean glucose",
+        value: convertGlucose(clinical.meanMgdl, "mg/dL"),
+        unit: "mg/dL",
+      });
+    }
   }
   if (clinical.gmi !== null) {
     push({