diff --git a/CHANGELOG.md b/CHANGELOG.md
index 88109be85..66418c187 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,12 @@
 # Changelog
 
+## [1.37.22] — 2026-08-15
+
+### Fixed
+
+- The doctor-report export refuses a selection that includes nothing instead of rendering an empty document. The selection panel already disabled its own button in that state, so this only ever reached the server through a hand-built request, and it spent an export slot on a file with no content in it.
+- A lab value in the FHIR export no longer names UCUM as its unit system when it carries no UCUM code. That combination told a receiving system the unit was coded when it was not, which is worse than saying nothing: the unit still travels as a display string, and the coded form appears only when the analyte and unit actually resolve to one.
+
 ## [1.37.21] — 2026-08-14
 
 ### Fixed
diff --git a/docs/api/openapi.yaml b/docs/api/openapi.yaml
index 33df1201c..a1f24e691 100644
--- a/docs/api/openapi.yaml
+++ b/docs/api/openapi.yaml
@@ -1,7 +1,7 @@
 openapi: 3.1.0
 info:
   title: HealthLog API
-  version: 1.37.21
+  version: 1.37.22
   description: >-
     Self-hosted personal-health-tracking PWA — public API surface for the iOS native client and external ingest.
 
diff --git a/package.json b/package.json
index d7cff0ed2..3a19812db 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "healthlog",
-  "version": "1.37.21",
+  "version": "1.37.22",
   "description": "Self-hosted personal-health-tracking PWA with Withings integration, AI insights, and doctor-report PDF export.",
   "license": "PolyForm-Noncommercial-1.0.0",
   "homepage": "https://healthlog.dev",
diff --git a/public/sw.js b/public/sw.js
index 82e5879f3..be5aaff9e 100644
--- a/public/sw.js
+++ b/public/sw.js
@@ -36,7 +36,7 @@ try {
 // v1.4.38.4 → v1.4.42. Do not hand-edit; bump `package.json` and rebuild.
 const CACHE_VERSION =
   (typeof self !== "undefined" && self.__APP_VERSION__) ||
-  /* @sw-version-fallback */ "v1.37.21";
+  /* @sw-version-fallback */ "v1.37.22";
 const STATIC_CACHE = `healthlog-static-${CACHE_VERSION}`;
 const PAGE_CACHE = `healthlog-pages-${CACHE_VERSION}`;
 // v1.18.6 — read-only data cache for a curated allowlist of safe GET `/api/*`
diff --git a/src/app/api/export/health-record/__tests__/route.test.ts b/src/app/api/export/health-record/__tests__/route.test.ts
index 3e7b5185b..9a761419c 100644
--- a/src/app/api/export/health-record/__tests__/route.test.ts
+++ b/src/app/api/export/health-record/__tests__/route.test.ts
@@ -205,6 +205,18 @@ describe("POST /api/export/health-record — validation", () => {
     expect(res.status).toBe(422);
   });
 
+  it("rejects a selection that admits nothing with 422", async () => {
+    // The panel disables its own submit in that state, so only a hand-built
+    // request gets here. Rendering an empty report and spending a rate-limit
+    // slot on it would be the wrong answer; this route has no documents-only
+    // mode that would make an empty leaf list a legitimate scope.
+    const { POST } = await import("../route");
+    const res = await POST(mkReq({ format: "pdf", selection: sel() }));
+    expect(res.status).toBe(422);
+    const body = (await res.json()) as { meta?: { errorCode?: string } };
+    expect(body.meta?.errorCode).toBe("export.selection.empty");
+  });
+
   it("rejects a userId smuggled into the body with 422", async () => {
     const { POST } = await import("../route");
     const res = await POST(
@@ -540,15 +552,11 @@ describe("POST /api/export/health-record — the selection reaches every format"
     // leaves: the totals must stay in the database.
     expect(await observationCodes(sel("LAB_RESULTS"))).toEqual([]);
     // And an empty selection — the "I said nothing" case, which used to mean
-    // "give me everything".
+    // "give me everything" and is now refused outright, so the totals cannot
+    // ride out on a scope nobody chose.
     const { POST } = await import("../route");
     const res = await POST(mkReq({ format: "fhir", selection: sel() }));
-    const bundle = (await res.json()) as {
-      entry: { resource: { resourceType: string } }[];
-    };
-    expect(
-      bundle.entry.filter((e) => e.resource.resourceType === "Observation"),
-    ).toEqual([]);
+    expect(res.status).toBe(422);
 
     // Asked for by name, they are emitted — the data is withheld, not lost.
     const asked = await observationCodes(sel("PHQ9_SCORE", "GAD7_SCORE"));
diff --git a/src/app/api/export/health-record/route.ts b/src/app/api/export/health-record/route.ts
index a9b7bfb14..758fc31e4 100644
--- a/src/app/api/export/health-record/route.ts
+++ b/src/app/api/export/health-record/route.ts
@@ -129,6 +129,17 @@ export const POST = apiHandler(async (request: NextRequest) => {
     );
   }
   const selection = minted.selection;
+  // A selection that admits nothing would render an empty report and still
+  // spend a rate-limit slot on it. The panel disables its own submit button
+  // in that state; a hand-built request has to be refused here, because this
+  // route has no documents-only mode that would make an empty leaf list a
+  // legitimate scope (the share-link route, which does, mints EMPTY itself).
+  if (selection.leaves.length === 0) {
+    annotate({ meta: { empty_selection: true } });
+    return apiError("Select at least one section to export", 422, {
+      errorCode: "export.selection.empty",
+    });
+  }
 
   const range = normaliseDateRange(input.range ?? undefined);
   const practiceName = sanitisePracticeName(input.practiceName);
diff --git a/src/lib/fhir/__tests__/lab-observations.test.ts b/src/lib/fhir/__tests__/lab-observations.test.ts
index 9c2c4080b..0feb2cc46 100644
--- a/src/lib/fhir/__tests__/lab-observations.test.ts
+++ b/src/lib/fhir/__tests__/lab-observations.test.ts
@@ -181,7 +181,12 @@ describe("lab-result FHIR Observations", () => {
 });
 
 describe("lab-result LOINC + canonical UCUM coding (v1.18.8)", () => {
-  function labOf(type: string, unit: string, value = 5.4) {
+  function labOf(
+    type: string,
+    unit: string,
+    value = 5.4,
+    bounds?: { low: number; high: number },
+  ) {
     const bundle = buildFhirDocumentBundle(
       makeData({
         labResults: [
@@ -191,8 +196,8 @@ describe("lab-result LOINC + canonical UCUM coding (v1.18.8)", () => {
             value,
             valueText: null,
             unit,
-            referenceLow: null,
-            referenceHigh: null,
+            referenceLow: bounds?.low ?? null,
+            referenceHigh: bounds?.high ?? null,
             catalogReferenceLow: null,
             catalogReferenceHigh: null,
             sourceReferenceText: null,
@@ -250,13 +255,15 @@ describe("lab-result LOINC + canonical UCUM coding (v1.18.8)", () => {
     expect(tsh?.valueQuantity?.code).toBe("m[IU]/L");
   });
 
-  it("omits the UCUM code when the unit does not match the mapped canonical", () => {
+  it("omits the UCUM code AND its system when the unit does not match the mapped canonical", () => {
     // HbA1c mapped (LOINC present) but recorded in an mmol/mol unit we don't
     // canonicalise → keep the LOINC coding, drop the UCUM code, keep display.
+    // The system goes with the code: a valueQuantity naming UCUM without a
+    // code claims a coding the bundle does not carry.
     const o = labOf("HbA1c", "mmol/mol", 36);
     expect(o?.code.coding?.[0].code).toBe("4548-4");
-    expect(o?.valueQuantity?.system).toBe("http://unitsofmeasure.org");
     expect(o?.valueQuantity?.code).toBeUndefined();
+    expect(o?.valueQuantity?.system).toBeUndefined();
     expect(o?.valueQuantity?.unit).toBe("mmol/mol");
   });
 
@@ -264,10 +271,25 @@ describe("lab-result LOINC + canonical UCUM coding (v1.18.8)", () => {
     const o = labOf("Selenium", "ug/L", 95);
     expect(o?.code.text).toBe("Selenium");
     expect(o?.code.coding).toBeUndefined();
-    // Display unit stays; no coerced UCUM code is invented.
+    // Display unit stays; no coerced UCUM code is invented, and no code
+    // system is named for a code that is not there.
     expect(o?.valueQuantity?.unit).toBe("ug/L");
     expect(o?.valueQuantity?.code).toBeUndefined();
-    expect(o?.valueQuantity?.system).toBe("http://unitsofmeasure.org");
+    expect(o?.valueQuantity?.system).toBeUndefined();
+  });
+
+  it("keeps system and code together on the reference range bounds too", () => {
+    // The bounds are stated in the SAME unit as the value, so an uncoded
+    // unit must leave them uncoded as well, on both halves.
+    const uncoded = labOf("HbA1c", "mmol/mol", 36, { low: 20, high: 42 });
+    expect(uncoded?.referenceRange?.[0].low?.system).toBeUndefined();
+    expect(uncoded?.referenceRange?.[0].low?.code).toBeUndefined();
+    expect(uncoded?.referenceRange?.[0].high?.system).toBeUndefined();
+    const coded = labOf("HDL", "mg/dL", 55, { low: 40, high: 60 });
+    expect(coded?.referenceRange?.[0].low?.system).toBe(
+      "http://unitsofmeasure.org",
+    );
+    expect(coded?.referenceRange?.[0].low?.code).toBe("mg/dL");
   });
 });
 
diff --git a/src/lib/fhir/resources/labs.ts b/src/lib/fhir/resources/labs.ts
index 43509310a..60b70d019 100644
--- a/src/lib/fhir/resources/labs.ts
+++ b/src/lib/fhir/resources/labs.ts
@@ -80,11 +80,14 @@ export function labObservations(
     // A lab quantity: the recorded `unit` is always the display string, and
     // the canonical UCUM `code` is stamped only when the analyte map resolved
     // one for exactly that unit (no coerced symbol).
+    // The `system` rides along WITH the code and never alone: naming UCUM as
+    // the code system while withholding the code claims a coding the bundle
+    // does not carry, and leaves a receiver unable to machine-compare the
+    // value it is attached to.
     const quantity = (value: number) => ({
       value,
       unit: lab.unit,
-      system: UCUM_SYSTEM,
-      ...(coding?.ucum ? { code: coding.ucum } : {}),
+      ...(coding?.ucum ? { system: UCUM_SYSTEM, code: coding.ucum } : {}),
     });
     // The bounds are stated in the SAME unit as the value, so they carry the
     // SAME coding — a bare unit beside a coded value leaves a receiver unable