Low vitamin D level (19), High phosphorus level (4.5), High PTH level (70). What could be the cause of this? Serum Calcium level is normal.

Treat low vit D. I would get the low vitamin D treated and then recheck the labs. The 25OH vit D should be above 30. This will likely correct any of the other mild reported lab abnormalities.
Vitamin D deficient. Deficiency of vitamin D will elevated the parathyroid hormone level. The phosphorus elevation is minimal. You need to address why you are vitamin D defricient, consider supplementing more than you are doing already, or if you're on a good oral dose, consider whether your "irritable bowel" might be lipid malabsorption. Get yourself a healthy amount of sunlight. Best wishes.

Related Questions

What causes you to have a borderline high calcium level but very very low Vitamin D Level for months now? Any diseases or disorders associated with this? PTH is normal, Albumin is normal and Phos norm

This is often seen. in fair complected people and may be a pre-cursor to Vit D Deficiency....you need NUTRITIONAL COUNSELING! Hope this helps! Dr Z. Read more...
Low vit D. If your calcium is borderline hight with a low vitamin d, fix the vitamin D deficiency. This will likely raise the calcium more. This should be done under doctor supervision with frequent lab monitoring. I would reassess you for hyperparathyroidism after your vitamin D is normalized. I suspect you have borderline (early) hyperparathyroidism. . Read more...