As Nikki said, those aren't the type of blood clots we worry about. Miserable and need to be treated and cause found, but not imminently fatal!
The blood clots we worry about are ones that build up in our veins or sometimes in arteries. The most common are a clot in the calf of the leg. When we begin to lose the ability to walk and especially as we rely on a wheelchair, blood flow in the legs is slowed and clots can form. A wheelchair ought to come with a recommendation to take at least a baby aspirin daily, but doctors have a bad habit of not considering this. Only after you have a blood clot do they get around to doing anything about prevention! A blood clot can break apart and send pieces floating through the blood only to stick in arteries supplying the brain or lungs. In brain they can cause a stroke, and in the lungs they are called a pulmonary embolus. A pulmonary embolism causes shortness of breath and possibly pain when breathing, making them very frightening. At least they make you go to the ER promptly. A clot in the leg (DVT, Deep Vein Thrombosis) is too often considered just swelling or a strained muscle, not a reason to get to a doctor or ER promptly. That gives the clot time to send a shower of pieces off into the blood stream and cause a stroke or pulmonary embolism.
So, your husband isn't in danger from blood clots in the bladder or urine but I have managed to give you other things to worry about in the future. Sorry about that! But clots are something every here needs to know about so I have blatantly hijacked your post!