Lab Test Stuff.txt

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Lab Test Stuff.txt
2012-01-06 00:57:03
Lab Test Stuff Family medicine

Laboratory tests - CBC
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  1. Lab Exam - CBC
  2. Adult with Hb 106 and MCV 72 - what kind of anemia?
    Microcytic anemia
  3. Differential diagnosis of microcytic anemia? (10)
    #1 Iron deficiency,thalassemias, chronic disease (rare, late stage), sideroblastic, lead, EtOH, drugs, Copper def, zinc poisoning, congenital
  4. #1 worldwide cause of iron deficiency anemia?
    Hook worm
  5. Causes of macrocytic anemia?
    Alcohol #1, B12 or folate, drugs (HIV anti-retrovirals, chemo/MTX, anti-epileptics), Myelodysplastic syndromes MDS, AML/ALL, liver disease, reticulocytosis (hemolysis, bleed, iron therapy), hyperlipidemia, congenital, thyroid, myeloma
  6. Clues about macrocytic anemia from the CBC?
    RDW - Increased (B12, folate, AIHA, drugs) vs Normal (sick bone marrow - MDS, myeloma)
  7. Ancillary tests for work-up of macrocytic anemia
    • #1 smear & retics - to r/o hemolysis and metabolic dz
    • B12 level, RBC folate (or plasma folate), methylemalonate (confirmatory for B12 def), homocysteine level
  8. More ancillary tests for macrocytic anemia - rare
    SPEP, UPEP, liver enzymes, TSH, coombs, haptoglobin, BM biopsy
  9. Normocytic anemia DDx
    Chronic disease, Chronic kidney disease (Epo def), iron deficiency (early), endocrine causes, BM suppression (cancer, aplastic)
  10. Clues on CBC for normocytic anemia w/u
    • RDW - Normal (Chronic disease)
    • WBC/plts - if both low then pancytopenia (aplastic anemia)
  11. 2 best ancillary tests for Normocytic anemia w/u
    Start with smear and retics
  12. If smear and retics not helpful in normocytic workup, what next?
    Do Cr to rule out CKD, but otherwise consult heme if going further
  13. Clues on CBC for Microcytic anemia
    • RDW - increased (Fe def), Normal (thalassemia, chronic disease)
    • Count - Increased (Thalass), Decreased (Fe def)
  14. Single best ancillary test for microcytic anemia
    Ferritin! But increased in inflammatory process (more common with inpatients)
  15. How to interpret ferritin results?
    • <10 - Dx for Fe deficiency, <30-40 (LR 11) very sense and spec for iron deficiency. If >100 then not Fe def (LR 0.1).
    • So if between 40 and 100 then can't tell.
  16. If Ferritin is equivocal for microcytic anemia work-up?
    • TIBC, Transferrin sat, Fe level (if ferritin between 40-100)
    • Hb electrophoresis if suspect thalassemia, hemoglobinopathy
  17. When to be more hasty with tests in microcytic anemia?
    If pregnant, want to Dx thalassemia or genetic Hb-opathy sooner than later, so do hb electrophoresis (SPEP) sooner.
  18. AAFP's approach to macrocytic anemia - 1st 3 tests to order?
    If MCV > 100, order a smear, retic count and B12 (interpret in that order)
  19. Interpret smear in macrocytic anemia workup?
    • If smear normal (not megaloblastic) - consider EtOh, drugs, thyroid, liver dz --> consider LFTs and TSH
    • If smear ban (megaloblastic) - then move onto retic count
  20. Interpret retic count in macrocytic anemia with megaloblastic on smear?
    • Retics > 2% = hemolysis (do hemolytic workup)
    • Retics < 2% = Look at B12 level
  21. Interpret B12 level in macrocytic, megaloblastic anemia with N retic count?
    • Vit B12 < 100 pg/ml --> B12 deficiency - treat
    • Vit B12 100-400pg/ml (74 - 294 pM/L) - indeterminate
    • Vit B12 >400 pg/ml (>294 pmol/L) - not B12 def… order RBC folate
  22. If indeterminate B12 level in megaloblastic anemia with N retics?
    B/w 100-400 pg/ml - check MMA and homocysteine
  23. Clues to MMA and homocysteine interpretation?
    • MMA HIGH (regardless of homocys)- Vit B12 def
    • MMA N + N homocysteine - BM Biopsy
    • MMA N + high homocysteine - Folate deficiency
  24. If smear megaloblastic, retics N, B12 > 400 pg/ml, what next?
    RBC Folate level (if low treat), if normal - BM Bx?
  25. Which results suggest iron def anemia?
    Increased RDW, low RBC count, low ferritin, low Fe, TIBC increased, transferrin sat decreased (only do last 3 if ferritin N)
  26. Which results suggest chronic disease anemia in microcytic workup?
    Low Fe, TIBC low, Transferrin sat decreased with high ferritin
  27. If patient has mild normocytic anemia with N RDW, WBC/plts N, no abN cells on smear, no Sx and known chronic disease? If not?
    Presumptive Dx of Anemia of CHronic Disease (ACD), if not - then repeat CBC and get corrected retic index (CRI)
  28. If normocytic anemia without obvious ACD and N or low CRI?
    • Either BM cause, Fe def or ACD.
    • Consider BM biopsy (if any of CRI<0.1%,low plts/WBC or leukoerythroblastic cells) or Ferritin.
  29. Thrombocytopenia workup - DDx
    clumping, pregnancy, iron def (severe), hypersplenism (if drinker), ITP, malignancy, TTP/HUS, drugs, infection (HIV, malaria), HIT, HELLP
  30. CBC clues of thrombocytopenia
    • MPV (mean platelet volume) - high with clumping, low with BM failure
    • Other cell lines - ? pancytopenia
  31. Ancillary tests for thrombocytopenia
    • Smear - fragments vs clumping vs other AbN cells
    • if unsure after this… heme consult
  32. What is platelet clumping due to and how to prevent it?
    2º to EDTA in medium. Repeat and order Non-EDTA on requisition.