Association of Calcium and Phosphate Levels with Incident Chronic Kidney Disease in Patients with Hypoparathyroidism: A Retrospective Case-Control Study

Figure 2

Selection of the study analysis cohorts. Ca: albumin-corrected serum calcium; Ca × P: calcium-phosphate product; CKD: chronic kidney disease; eGFR: estimated glomerular filtration rate; P: serum phosphate; rhPTH(1–84): recombinant human parathyroid hormone (1–84). Patients with CKD must have had a diagnosis of CKD after the index date to be eligible. Patients with a diagnosis of CKD before the index date were excluded. The first indicator of CKD after the index date was defined as the outcome date for patients who developed CKD, and a matched date was chosen for controls. ^†The exposure window for patients who developed CKD was the time from the index date to the first diagnosis of CKD (the first eGFR <60 mL/min/1.73 m² or the first CKD diagnosis code). The eligible window for patient controls was the time from the index date to the end of data availability or the day before CKD diagnosis, whichever occurred earlier. In risk-set sampling, patients who developed CKD were eligible to be chosen as potential controls during the time window before CKD diagnosis. ^‡Patients with CKD and controls analyzed for the exposures of P and Ca × P were those who had at least one set of measurements for Ca and P available on the same day. ^§Matched 1:1 on age ± 5years, sex, index date ± 1 year, and duration of exposure window.