ERM2 - Endocrine Tests

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ERM2 - Endocrine Tests
2012-11-20 00:25:44
Endocrine Reproductive Pathology

Endocrine and Reproductive Pathology
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  1. 24 Hour Urine Collection
    -quantify metabolites with episodic or circadian fluctuations or quantify dietary intake

    • -empty bladder at time 0 and discard urine
    • -collect urine until 24 hrs and store at 4C

    • -sample needs to be acidified with HCl to keep Ca soluble
    • -certain bacterial infections produce urease --> alkaline urine and stones
  2. 24 Hour Urine Collection: Over or under collection
    • Urine volume should be btwn 1-2L
    • - <500cc --> undercollection

    • Urine Creatinine should be ~20mg/24hr/kgBW
    • -(1-2g creatinine in 24 hours)
  3. Creatine and Creatinine
    • -energy from ATP is stored in phosphcreatine in muscle
    • -fixed percent of Phosphocreatine spontaneous decomposes to creatnine which is excreted in urine
  4. Free vs Total T4/T3
    • -total T3/T4 is almost entirely bound to proteins
    •      -TBG
    •      -albumin
    •      -pre-albumin (transthyretin)
    • -free T3/T4 is biologically active
  5. T4 analog assay
    • -T4 analog doesn't bind TBG (always free) but is recognized by anti-T4 ab
    • -patient's free T4 competes with the analog for binding to the ab

    • -elevated free T4 --> decreased analog binding
    • MAJOR EXCEPTION: unreliable during pregnancy when TBG is high due to estrogen and albumin is low due to volume dilution
  6. T3 Resin Uptake
    • -mix patient plasma with resin and a radioactive T3 tracer
    • -normally empty sites on TBG capture most of the tracer and only some binds resin (~30%)

    Increase resin uptake in normal total T4: excess T4

    • Decreased resin uptake in normal total T4: decreased T4
  7. T3 resin uptake equation
    free T4 levels = (total T4) x (T3 resin uptake)
  8. T3 resin uptake in pregnancy
    -increased TBG leads to increased total T4 (lower resin uptake)

    -elevated total T4 with decreased T3 resin uptake --> euthyroid

  9. Forms of Calcium in the blood

    • Total Ca: mg/dL
    • Ionized Ca: mM or mEq/L
  10. Normal Ionized Ca in hypocalcemia
    • -in illness albumin is often less than normal
    • -less Ca is protein bound
    • -more Ca is ionized
  11. Albumin Corrected Ca Level
    • -rough correction
    • -when albumin drops by 1gm/dL total Ca should drop by 0.8mg/dL
  12. Acidity and Plasma Ca Levels
    • -acidity prevents Ca from binding to albumin
    • -also prevents Ca from precipitating

    • Acidemia --> increased ionized Ca
    • Alkalemia --> decreased ionized Ca

  13. Room Air contamination and Ca Levels
    • -when blood is exposed to room air CO2 is lost --> artificial alkalosis
    • -this gives a falsely low ionized Ca
    • -hyperventilation lowers ionized Ca
  14. Band Keratopathy
    • -in hyperparathyroidism iCa is elevated
    • -Ca precipitates in horizontal bands where the eyelids meet (increased pH due to exposure to air)
  15. GI effects of pH on Ca
    • -gastric acid helps dissolve CaCO3 tablets
    • -CaCO3 should be taken with meals (increased acid)
    • -PPI, mucosal atrophy --> poor absorption of CaCO3
  16. Trabecular bone
    • -cancellous
    • -increased surface area
    • -prone to rapid resorption (bone loss)
  17. Cortical bone
    • -compact
    • -increased density (stronger)
  18. Osteoporosis
    -systemic disease characterized by low bone mass with microarchitecture deterioration

    -increased susceptibility to fracture

    -bone density peaks at 30yrs
  19. Bone Strength
    • 1. Bone Mineral Density
    • 2. Bone Quality
  20. Ways to measure BMD
    • 1. QCT (volume)
    • 2. DXA (area)
  21. Hounsfield unit
    • -radio opacity
    • -converted to BMD by comparing to 5 element calibration phantom with known Ca concentration
  22. DXA
    • -dual energy xray absroptiometry
    • -differential attenuation of xrays by bone and soft tissue
    • -use xrays of 2 different energy levels
    • -larger bone appears more dense because it's thicker
  23. T score
    -compares with young adults of the same gender
  24. Z score
    • -compares with age-matched cohort
    • -same weight, gender and ethnicity

    -more accurate in older patients
  25. Osteopenia
    t score -1 to -2.49
  26. Osteoporosis
    t score < -2.5


    fragility fracture regardless of t score
  27. Least Significant Change (LSC) on DXA
    • -the smallest difference between two measurements that is indicative of a real change
    • -depends on instrumentation and techniques
    • -obese patients have a higher LSC

    • lean pts: 0.02
    • obese pts: 0.03