low levels of the neurotransmitter low levels of the neurotransmitter serotonin low levels of thyroid hormone low levels of thyroid low levels of thyroxine low levels of thiamine low levels of testosterone in males low levels of thyroid stimulating hormone low levels of thyroid hormones hypothyroidism low levels of testosterone low levels of testosterone in women low levels of testosterone in men low levels of testosterone icd 10 low levels of testosterone in females alkaline phosphatase low levels meaning ferritin levels low hematocrit low levels meaning hemoglobin levels low ast low levels meaning bun low levels mean alt low levels meaning albumin levels low low levels of vitamin d low levels of serotonin low levels of potassium