Hypothyroxemia Guidelines - Thyroxine Deficiency

1. Thyroid Screening
   
   
   1. Pregnancy
      
      
      1. TSH (Thyroid Stimulating Hormone)
         
         1. TSH <2.0 MIU (<20weeks)
         2. TSH <2.5 MIU (>20weeks)
         3. increases from 10-20weeks, HCG depression
            
            
      2. FT4 (Free Thyroxine, FreeT4)
         
         1. FT4 >20%ile (<20 weeks) [ie, .8 for 0.6-1.6 ng/ml]
         2. FT4 >10%ile (>20 weeks) [ie, .7 for 0.6-1.6 ng/ml]
         3. higher in early pregnancy than non-pregnant, falls with GA but still in normal range, HCG stimulates, Estradiol decreases
            
            
      3. Repeat q4-6 weeks (non-pregnant and first trimester), q8weeks 2nd and thrid trimester, as close to next dose as possible, late afternoon (diurnal, low at midnite)
         
         
      4. Other Labs to consider
         
         1. Antithyroid Antibodies: TPO-microsomal, ATG (antithyroglobin) [if FreeT4 <10%ile]
            1. Fetal effects
         2. Iodine Deficiency
            1. Urinary 24 hour iodide: should be >100mcg/24hr (normal 100-500)
            2. FreeT3: FT3/FT4 molar ratio >2.5 if Iodine deficient or subclinical
            3. TSH: increases from 20-40 weeks if Iodine deficient
            4. Thyroglobin (TG): elevation correlates with degree of Iodine Deficiency
               
               
   2. Non-Pregnancy
      
      
      1. TSH <2.5 (Consider AACE recommendations)
      2. FreeT4 in normal range
         
         
2. Treatment
   
   
   1. L-thyroxine Full Replacement Dosing***
      Estimate 1.7mcg/kg/day qhs
      1. Pregnancy may require ~25% increase, more with increased GA
      2. 1hour after any food, dose depends on brand
      3. FreeT4 maintain upper normal vs clinical improvement?
      4. TSH can be low in 10-20%
      5. Iron supplements inhibits absorption
         
         
   2. L-thyroxine Sub-normal/Subclinical Dosing***
      These require much lower dosing and individualization, highly variable
      
      
   3. Iodide, 200mcg/day if deficient
      
      
3. Symptoms
   
   
   1. Low Thyroid (Hypothyroid)
      
      1. Fatigue/Somnolence
      2. Cold intolerance
      3. Dry skin, dry hair
      4. Constipation
      5. Depression
      6. Weight Gain
      7. Memory Loss
      8. Anemia
      9. Hypertension/Preeclampsia
      10. Diabetes Mellitus/ Glucose Intolerance
      11. Placental Abruption
      12. Arrythmias
      13. Failure to progress
      14. Large birthweight (mild), Low birthweight (severe)
      15. Hydramnios
          
          
   2. High Thyroid (Hyperthyroid)
      
      1. Insomnia
      2. Diarrhea
      3. Feeling hot and sweaty
      4. Weight loss
      5. Tachycardia/Palpitation
      6. Hypertension
      7. Seizures
      8. Irritability
         
         
4. Mean Values in Pregnancy (Resnik and Creasy p985)
   
   
   
5. Problems to consider
   
   
   1. FreeT4 assays are not standardized for pregnancy
   2. Levels non-normal distribution
   3. Labs vary with pregnancy and gestational age
   
   

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