Urinary Tract Infection (UTI): Given the patient's age, underlying conditions (dialysis or diabetic nephropathy), and symptoms of dysuria and difficulty passing urine, a UTI is the most plausible diagnosis. The compromised renal function and potential for urinary stasis increase the risk of infection.

Urinary Retention: This could be due to various factors including benign prostatic hyperplasia (BPH), neurogenic bladder, or even medication side effects. The difficulty in passing urine is a key symptom.
Kidney Stone: Although less common in patients with end-stage renal disease, kidney stones can still occur and cause severe pain and difficulty urinating.
Catheter-Associated UTI: If the patient has a urinary catheter, there's an increased risk of developing a catheter-associated UTI, which could explain the acute onset of symptoms.

Sepsis: Although less likely as an initial diagnosis, sepsis can quickly develop from a UTI, especially in immunocompromised patients or those with chronic conditions. It's crucial to identify and treat promptly to avoid high mortality rates.
Obstruction of the Urinary Tract: This could be due to stones, blood clots, or other causes. In a patient with one kidney or significant renal impairment, obstruction can lead to rapid deterioration of renal function.
Prostate Cancer: While not immediately life-threatening like sepsis, prostate cancer can cause urinary retention and should be considered, especially in older males with symptoms of urinary obstruction.

Fungal Infection: In patients with significant immunocompromise or on long-term antibiotics, fungal infections of the urinary tract can occur, though they are less common.
Tuberculosis of the Urinary Tract: This is a rare condition in many parts of the world but should be considered in patients with exposure history or risk factors.
Malignancy of the Urinary Tract: Cancers of the bladder, ureters, or kidneys can cause similar symptoms but are less common than other diagnoses listed here.