Brief Answer: Thyroid ; diabetes Detailed Answer: Inadequately treated hypothyroidism can cause worsening of glucose intolerance. In those predisposed to it from various other causes such as PCOS for example, can potentially decompensate into diabetes. However, before formally starting diabetes treatment, it is worthwhile optimally dosing thyroid medication to target a TSH of 0.4 to 2. After achieving stable thyroid replacement, it is helpful to check the glucose tolerance again to see if the diabetes has reversed to pre-diabetes or normal range. There is an exception, of course to not treating diabetes. If the sugars are really high , for instance close to 200 then formal treatment may need to begin simultaneously. Further, the TSH targets also depend on the individual circumstance. Those who have had thyroid cancer followed by thyroid removal surgery within previous 5 years typically are given higher than normal thyroid doses to keep the TSH suppressed to below 0.1. Furthermore, those with severe (especially untreated) osteoporosis, chest pain from heart disease or irregular heart rhythm problems are generally prescribed lower than usual doses.

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