Final answer:
A decreased calculated glomerular filtration rate (GFR) indicates that the patient's CKD is getting worse.
Step-by-step explanation:
The serum laboratory value that indicates to the nurse that the patient's CKD is getting worse is a decreased calculated glomerular filtration rate (GFR). GFR measures the rate at which the kidneys are filtering waste from the blood, and a decrease in GFR indicates worsening kidney function. Other laboratory values, such as decreased BUN (blood urea nitrogen), sodium, and creatinine, may also be abnormal in CKD, but a decreased GFR is specifically associated with worsening kidney disease.