What is the most appropriate next step in management?

A 56-year-old man attended routine follow-up for treatment of hypogonadism of late onset. His only medication was testosterone undecanoate (1 g intramuscular injection, every 12 weeks). He had started this treatment 12 months previously and last received the injection 1 week before review.

Digital rectal examination was normal.

Investigations (baseline):

haemoglobin145 g/L (130C180)

haematocrit0.46 (0.40C0.52)

serum prostate-specific antigen0.6 µg/L (<4)

Investigations (12 months after treatment):

haemoglobin153 g/L (130C180)

haematocrit0.51 (0.40C0.52)

serum prostate-specific antigen5.1 µg/L (<4)

What is the most appropriate next step in management?
A . check serum testosterone
B . decrease testosterone injection frequency to 14 weeks
C . reassure and repeat blood tests in 12 months
D . refer for urological assessment
E . stop testosterone therapy