high levels of parathyroid hormone (PTH) can indicate a vitamin D deficiency. The "normal level" of 25(OH) D is 80 ng/ml (200 nmol/L). That is the level our body sets as it's normal limit when we don't limit sunshine.  For some people like me it takes 10,000 IU a day to maintain that.  Lack of enough sun and malabsorption of vitamin D orally.  

No, all this is related to calcium. Why would I then have a low ionized calcium level and a high PTH (hormone that controls the balance of blood calcium)? Your thiamine story doesn't hold up.

Welcome to the forum, @Allias, For the growth and maintenance of bones, more vitamins and minerals are needed than those you are taking.   Bones need calcium, as well as magnesium and iron, but also trace elements like zinc, copper, selenium, manganese, and boron.   Bones need vitamins like Vitamin D and Folate (not synthetic Folic Acid which the body doesn't utilize well), but bones also need Vitamin A,  Vitamin K, Cobalamine B12, Pyridoxine B6, Riboflavin B2, Choline B4, and Thiamine B1.   High PTH and high alkaline phosphatase (ALP) levels may indicate a deficiency in Thiamine B1.  The enzyme Alkaline phosphatase combines with Thiamine to make Adenosine Triphosphotase (ATP), the "energy coinage" used in the body which is required to build bones or perform any body function.  Increased levels of ALP and PTH are produced when there's not sufficient Thiamine to meet the demands.  Bones, the liver, the thyroid and the gastrointestinal tract can all make ALP when there's a shortage of Thiamine in each of those organs.  The gastrointestinal tract makes ALP when increased thiamine absorption is required.  Thiamine is needed to attach to calcium so it can be absorbed.   Thiamine deficiency disorders include muscle spasms in muscles like the neck muscles, and neuropathy.   What is your Vitamin D level? Do talk to your doctor and nutritionist about supplementing with essential nutrients while recovering.   References: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7914453/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7352179/   https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6459027/ https://pubmed.ncbi.nlm.nih.gov/4003329/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10568373/ https://pubmed.ncbi.nlm.nih.gov/36428888/ https://pubmed.ncbi.nlm.nih.gov/1156856/ https://pubmed.ncbi.nlm.nih.gov/38034619/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10398819/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8451766/

With the range and units it does not make any sense for that test to be for Tissue transglutaminase IgA.  That normal range would be very logical for total IgA.  Please ask your GP when you see him/her.

Just repeating what my gastroenterologist was saying. Sorry - not a helpful post of mine, as I wasn't even sure what he meant!