Zig,
First, way to tough it out! Since you are able to go hard, and have completed a 1/2IM your real-world and laboratory testing seems to indicate you've managed this challenge well. If you were able to "race" the 1/2 it would seem that if you were to have a problem with dehydration and kidney functioning it would have shown up. Where you might want to raise questions is how to manage volume depletion, rehydration, and electrolyte replacement for the IM distance. The upside to IM is that you will not be going at your 1/2IM pace (tip!) so mangement of this can be easier. The race, however, is longer and so more opportunity to get in trouble. I would think knowing your sweat-rate would help. Calculating fluid and electrolyrte replacement from that along with comparing those numbers to your 1/2IM intake of same should give you ballpark what you will need. The one thing you could do, just thinking out loud here, if you needed the peace of mind and with your Dr's support of course, is to do a longish brick at IM race pace, hydrate and replenish according to the plan, and ask the Dr to run the appropriate panels to test kidney, electrolyes, or whatever else might be a concern. It would seem to me that if there were issues you would know. Lastly, I would ask the doc what are the signs/symptoms that would indicate I'm headed for trouble and what to do about them.
First, way to tough it out! Since you are able to go hard, and have completed a 1/2IM your real-world and laboratory testing seems to indicate you've managed this challenge well. If you were able to "race" the 1/2 it would seem that if you were to have a problem with dehydration and kidney functioning it would have shown up. Where you might want to raise questions is how to manage volume depletion, rehydration, and electrolyte replacement for the IM distance. The upside to IM is that you will not be going at your 1/2IM pace (tip!) so mangement of this can be easier. The race, however, is longer and so more opportunity to get in trouble. I would think knowing your sweat-rate would help. Calculating fluid and electrolyrte replacement from that along with comparing those numbers to your 1/2IM intake of same should give you ballpark what you will need. The one thing you could do, just thinking out loud here, if you needed the peace of mind and with your Dr's support of course, is to do a longish brick at IM race pace, hydrate and replenish according to the plan, and ask the Dr to run the appropriate panels to test kidney, electrolyes, or whatever else might be a concern. It would seem to me that if there were issues you would know. Lastly, I would ask the doc what are the signs/symptoms that would indicate I'm headed for trouble and what to do about them.