A 73-year-old man comes to the office due to 3 months of progressive urinary urgency, hesitancy, nocturia, and weak urinary stream. He has no fever, abdominal pain, hematuria, malaise, or weight loss. His only medication is lisinopril for essential hypertension. The patient has no history of diabetes mellitus or ischemic heart disease. He does not use tobacco, alcohol, or illicit drugs. Digital rectal examination reveals a smooth, firm, and enlarged prostate without induration or asymmetry. Neurological examination is normal. Urinalysis shows no proteinuria or hematuria. The patient's serum creatinine is 2.1 mg/dL, which is higher than his baseline creatinine of 1.2 mg/dL 4 months ago. Prostate-specific antigen is normal. Which of the following is the most appropriate next step in evaluation of this patient's acute kidney injury?

Question

A 73-year-old man comes to the office due to 3 months of progressive urinary urgency, hesitancy, nocturia, and weak urinary stream.  He has no fever, abdominal pain, hematuria, malaise, or weight loss.  His only medication is lisinopril for essential hypertension.  The patient has no history of diabetes mellitus or ischemic heart disease.  He does not use tobacco, alcohol, or illicit drugs.  Digital rectal examination reveals a smooth, firm, and enlarged prostate without induration or asymmetry.  Neurological examination is normal.  Urinalysis shows no proteinuria or hematuria.  The patient's serum creatinine is 2.1 mg/dL, which is higher than his baseline creatinine of 1.2 mg/dL 4 months ago.  Prostate-specific antigen is normal.  Which of the following is the most appropriate next step in evaluation of this patient's acute kidney injury?

Quizplus · Accepted Answer

This patient has lower urinary tract symptoms (LUTS) (eg, urinary urgency, hesitancy, nocturia, weak urinary stream) with a smooth, enlarged prostate on examination consistent with benign prostatic hyperplasia (BPH). Initial evaluation of patients with LUTS should include a urinalysis (to exclude infection and hematuria) and serum prostate-specific antigen (PSA) to assess risk for prostate cancer. A serum creatinine test is not required in the routine evaluation of uncomplicated BPH. However, it is recommended by some expert panels, especially for patients with more significant symptoms or additional risk factors (eg, hypertension, diabetes) for chronic kidney disease. This patient has evidence of acute kidney injury, as indicated by an interval rise in serum creatinine. Creatinine is generally not elevated in unilateral urinary obstruction (eg, ureteral calculus) but can be elevated in bilateral obstruction, such as in patients with severe bladder outlet obstruction due to BPH. Patients with acutely elevated creatinine require imaging (preferably renal ultrasound) to assess for hydronephrosis and exclude other causes of obstruction. Placement of a urinary catheter in patients with hydronephrosis can provide quick relief of the obstruction. (Choices A and E) Cystoscopy in patients with BPH can reveal signs of chronic bladder obstruction, but it is nonspecific and usually reserved for those who have failed initial management. It is also used to visualize the lower urinary tract in patients with hematuria, usually in combination with imaging of the upper tract (eg, CT scan of the kidneys and ureters). Urine cytology is sometimes performed in place of cystoscopy for low-risk patients with hematuria. Cytology can also be done for patients with LUTS and additional risk factors for bladder cancer (eg, smoking). (Choice B) Kidney biopsy is used to diagnose intrinsic renal causes of acute kidney injury. This patient's presentation is more consistent with obstructive (post-renal) acute kidney injury. (Choice C) Prostate biopsy is indicated for patients with signs of prostate cancer, such as grossly asymmetric enlargement of the prostate, palpable nodules, or persistently elevated PSA levels >4 ng/dL. Educational objective: Patients with severe bladder outlet obstruction due to benign prostatic hyperplasia can develop acute kidney injury. A renal ultrasound is advised for assessment of hydronephrosis in those with worsening kidney function. References: Clinical utility of gray scale renal ultrasound in acute kidney injury. (http://www.ncbi.nlm.nih.gov/pubmed/24011084)

A 73-Year-Old Man Comes to the Office Due to 3