Brief Answer:
further evaluation needed...

Detailed Answer:
Hello and Welcome to 'Ask A Doctor' service...
I've gone through your query in details...
I can understand your concerns...

Well, first of all, it's important to know the colour of that semen.

Could you kindly recall?
Was it bright red or brownish-black/dark colour?

If it's brownish/blackish colour, then that single isolated episode could be due to a brief period of abstinence and is a part of stagnation of ejaculates (normal physiological phenomena). In that case, as things get regularize, it tends to come back to its usual colour. Which actually explains why there was no repetition of this during subsequent ejaculations.

Sometimes, excessive tobacco, alcohol, caffeine consumption (if at all do), in turn, can cause such discolouration. Dehydration itself is another cause, so if you feel any of these above, just act accordingly and it should be rectified within a matter of time only. Drink plenty of water, and observe for the time being...

However, if it was bright red, or there's any further recurrence then there's further evaluation needed...

Considering your age, to conclude the diagnosis, a thorough evaluation by your Physician/Urologist along with a few relevant investigations are necessary (namely serum PSA, Urine as well as prostatic secretion routine microscopy, culture sensitivity assay, Ultrasound KUB and prostate) to look into it further...management can be done based on the findings...

Since your physical is coming up, please discuss this with your doctor and proceed further...

Meanwhile, please drink plenty of water (around10 cups per day at least)...Avoid irritant foods like too much coffee, tea and carbonated drinks, some acidic fruits i.e. oranges, grapefruits, limes, spicy foods for the time being.

Let me know if I can assist you further.

Take Care
Kind Regards

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