A 30-Year-Old Woman Comes to the Office Due to Tingling

A 30-year-old woman comes to the office due to tingling and numbness in both of her distal lower extremities for the last 3 months.  Her symptoms are gradually worsening.  She also has had intense fatigue.  She has not had any weight change, constipation, skin dryness, headaches, or visual changes.  The patient was diagnosed with primary hypothyroidism secondary to Hashimoto thyroiditis when she was 10 years old.  She is currently on 100 mcg per day of levothyroxine orally.  Her mother also has hypothyroidism.  The patient does not use tobacco, alcohol, or recreational drugs.  Her menstrual cycles have been irregular for the last 6 months.  Her last menstrual period was 2 months ago.  She is sexually active with one partner.  Blood pressure is 114/78 mm Hg and pulse is 72/min.  She weighs 69 kg (152 lbs) and is 163 cm (5'4") tall.  Her thyroid is nonpalpable.  Her mucous membranes are moist and pale.  Her tongue appears to be bald.  She does not have any scleral icterus.  Vibration and proprioception are decreased in both of her lower extremities distally.  Pain and temperature sensations appear normal.  Her ankle jerks are absent, but other reflexes are brisk.  Babinski is present, and Romberg signs is positive.  The rest of the physical examination is unremarkable.  Stool obtained from the rectal examination is negative for occult blood.  Laboratory results reveal a hemoglobin of 8 g/dL and hematocrit of 24%.  Her total leukocyte count is 3,200/mm³.  Her platelet count is 300,000/mm³.  Basic serum chemistries are within normal limits.  Her total T4 level is 8.2 mcg/dL (normal 4-12 mcg/dL) and TSH level is 2.4 micro IU/mL. Which of the following is most crucial to monitor during the first few days of treatment in the above patient?

A) TSH level
B) Hemoglobin level
C) Serum potassium level
D) Platelet count
E) White blood cell count