AST AND ALT are both liver enzymes used to break down nutrients. These are called transaminases because they move the amino ring out of certain amino acids. These are the standard liver function tests. In cases of liver malfunction, excesses of these can end up in the blood.

Isolated excess in the blood of one or the other or specific combinations of enzymes can indicate other types of conditions.

Some meds can cause elevated levels of some of these (and other) liver enzymes. This needs to be taken into account when interpreting lab findings, but high levels must always be monitored, and any offending drugs might need to be removed or reduced.

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Thyroid stimulating hormone (TSH) is a hormone produced by the pituitary gland. T4 is produced by the thyroid.

Here is a very simplistic explanation of how TSH and T4 are related. TSH is the pituitary's messenger to the thyroid, to stimulate the thyroid to make more T4. The pituitary "sees" what circulating levels of T4 are. If they are too low, the pituitary says, "Hey Thyroid, wake up, work harder!". It says this by making more TSH. If there is too much T4, the pituitary will make less TSH, telling the thyroid to slow down.

With a normally functioning thyroid and pituitary gland, this chemical dialog between them maintains a perpetual equilibrium, where both TSH and T4 remain within "reasonable" levels (expected clinical range).

In the case of a thyroid that is underactive, it can't meet the pituitary's "request" (TSH). So you end up with high TSH, but low T4 (output by thyroid). High TSH + Low T4 = hypothyroidism.

In the case of an overactive thyroid, which puts out too much T4, the pituitary downregulates its own output of TSH. This is like saying to the thyroid, "Hey, you're overdoing it! Slow down!" But the thyroid is manic, can't slow down, and keeps on pumping out T4. So then you have the opposite situation: low TSH + High T4 = hyperthyroidism. -- edited to corrrect


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