fix(mimic-iv): filter MCHC to g/dL rows in complete_blood_count

Itemid 51249 is sometimes recorded with valueuom '%' in labevents.
Keep only g/dL values when building the derived MCHC column.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: Chessing234

mimic-iv/concepts/measurement/complete_blood_count.sql

@@ -8,7 +8,11 @@ SELECT
     , MAX(CASE WHEN itemid = 51221 THEN valuenum ELSE NULL END) AS hematocrit
     , MAX(CASE WHEN itemid = 51222 THEN valuenum ELSE NULL END) AS hemoglobin
     , MAX(CASE WHEN itemid = 51248 THEN valuenum ELSE NULL END) AS mch
-    , MAX(CASE WHEN itemid = 51249 THEN valuenum ELSE NULL END) AS mchc
+    , MAX(
+        CASE
+            WHEN itemid = 51249 AND valueuom = 'g/dL' THEN valuenum ELSE NULL
+        END
+    ) AS mchc
     , MAX(CASE WHEN itemid = 51250 THEN valuenum ELSE NULL END) AS mcv
     , MAX(CASE WHEN itemid = 51265 THEN valuenum ELSE NULL END) AS platelet
     , MAX(CASE WHEN itemid = 51279 THEN valuenum ELSE NULL END) AS rbc
@@ -30,6 +34,8 @@ WHERE le.itemid IN
         , 51301  -- WBC
     )
     AND valuenum IS NOT NULL
+    -- MCHC (51249) is sometimes recorded with valueuom '%' in error; keep g/dL only
+    AND (itemid != 51249 OR valueuom = 'g/dL')
     -- lab values cannot be 0 and cannot be negative
     AND valuenum > 0
 GROUP BY le.specimen_id