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How and When to Order Blood Tests

How and When to Order Blood Tests

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How and When to Order Blood Tests

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  1. How and When to Order Blood Tests Tammy Pifer Than, MS, OD, FAAO Carl Vinson VAMC Dublin, GA tammy.than@va.gov

  2. Getting the Job Done... • PCP • External laboratory • In-office sampling • is it ok?

  3. Before You Order Tests... • good case hx • narrow ddx • avoid “shot gun” approach • comprehensive ocular exam

  4. If You Order Tests... • interpret • Laboratory Tests and Diagnostic Procedures • 4th edition - 2004 • Chernecky and Berger • includes Herbal interactions • ISBN 0721603882 • $41.95 • communicate • treat • refer

  5. Random Blood Glucose • note when patient ate last • e.g. 220 mg/dL pp 3 hours • pp = post-prandial • diabetic if: •  200 mg/dL with symptoms • can do in-office • encourage patients to do this!

  6. Glycosylated Hemoglobin • HbA1c • checks long-term control • glycosylated HgB stays with RBC for its entire life • not diagnostic test? • normal = 4.3-6.1% • diabetic goal < 7.0% • ask patients!

  7. Fasting Plasma Glucose • fluctuating vision • get stable reading before new SpRx • retinopathy • diplopia • vascular occlusions • optic neuropathy

  8. CASE EXAMPLES

  9. Case #1. This is an easy one! • 17 year old male • CC: eyes look “real bad” • Symptoms: no pain • Pertinent Hx: county fair last night

  10. Subconjunctival Hemorrhage • History • frequency • medications • activity • Examination

  11. Subconjunctival Hemorrhage • Blood pressure • CBC with differential • PT (prothrombin time) • PTT (partial thromboplastin time) • or APTT (activated PTT) • INR (international normalized ratio)

  12. Prothrombin Time (PT) • prothrombin: • vitamin-K dependent glycoprotein produced by liver • needed for firm fibrin clot formation • PT – measures time for clot formation • reagent tissue thromboplastin and calcium are added to citrate plasma • avoid coffee and alcohol for 24 hours before test

  13. Prothrombin Time (PT) • each lab has normal value • normal range is  2 secs • Adult 10-15 sec • International Normalized Ratio (INR) • standardizes PT results • INR = (Patient’s PT in seconds)ISI Mean normal PT in seconds • ISI = international sensitivity index • Coumadin therapy

  14. Partial Thromboplastin Time (PTT) • evaluates how well coagulation sequence is functioning • time for recalcified, citrate plasma takes to clot after partial thromboplastin is added • Activated PTT • commercial activating materials used to standardize the test • current method of the test • Standardized times reported by each lab • < 35 seconds

  15. CBC with differential • routine part of health care • inexpensive • screening: • anemia • leukemia • infection • inflammation

  16. WBC (Part of CBC) • Total • overall number • first line of defense • decreased in aplastic anemia • elevated in infections, leukemia

  17. WBC (Part of CBC) • Differential • 100 white blood cells • % of each • neutrophils • lymphocytes • monocytes • eosinophils & basophils

  18. CBC • RBC count • hemoglobin • morphology • hematocrit • volume of RBC in 100 mL • 3 x Hgb • platelets

  19. Coagulation Studies • recurrent subconjunctival hemorrhages • non-traumatic hyphema • artery or vein occlusion • pre-op cataract surgery?

  20. Case #2. To Treat or not to Treat. • 34 YOWF • CC: HAs, double vision, dizzy • OHx: no trauma, LEE in 1999 - normal • MHx: Voltaren, Zantac

  21. Exam Findings • 20/20 OD; 20/20 OS • PERRL / (-)APD • partial 6th nerve palsy (OS) • visual field defects • superior nasal step OD • increased blind spot OS

  22. Fundus: What’s Your Diagnosis? • papilledema • R/O mass • R/O infection • placing your bets... • Idiopathic Intracranial Hypertension

  23. Workup • CT or MRI • unremarkable • LP • normal CSF content • elevated pressure

  24. Management • weight loss • acetazolamide • Diamox • steroids?? • ON sheath decompression • LP shunt

  25. Before you prescribe Diamox • baseline electrolytes • CBC with differential • R/O blood dyscrasias • monitor every 6 months

  26. Electrolytes • Na+ • 135.0 – 145.0 mmol/L • K+ • 3.60 – 5.00 mmol/L • Cl- • 101.0 – 111.0 mmol/L

  27. CO2 total content blood • 21.0 – 31.0 mmol/L • Increased • alcoholism • airway obstruction • pneumonia • drugs (e.g. antacids) • Decreased • dehydration • Diamox • measures compliance - < 20 mEq/L • tetracyclines

  28. SMA-6 • Sequential multiple analyzer (SMA) • automated system that analyzes multiple blood values from one tube of blood • SMA-6 • Carbon dioxide • Chloride • Creatinine • Potassium • Sodium • Urea nitrogen

  29. SMA-7 • Carbon dioxide • Chloride • Creatinine • Glucose • Potassium • Sodium • Urea nitrogen

  30. SMA-12 • Albumin • Alkaline phosphatase • Aspartate aminotransferase • Bilirubin • Calcium • Cholesterol • Glucose • Lactate dehydrogenase • Phosphorus • Protein • Urea nitrogen • Uric acid • Also SMA-20

  31. Eyelid Xanthoma • dermis infiltrated with xanthoma cells • yellow bilateral plaque • medial aspect UL • management: • cautery • laser • anything else?

  32. Lipid Panel/Profile • 12 hour fasting • total cholesterol • LDL • Usually calculated • LDL = cholesterol X (HDL+Triglycerides)/2 • HDL • triglycerides • risk for CAD • ratio total cholesterol / HDL

  33. Cholesterol • over half of adults in US have cholesterol > 200 mg/dL • desirable: 160-200 mg/dL • borderline: 200-239 mg/dL • high  240 mg/dL • Outside US • cholesterol x 0.0259 mmoles/L (international units) • 200 mg/dL = 5.18 mmol/L

  34. More Numbers… • HDL • good  35 mg/dL • women probably  45 mg/dL •  1 mg/mL risk of CHD  2-3% • Helsinki Heart Study (gemfibrizol in men ) • LDL • good < 130 mg/dL • high  190 mg/dL • Ratio (Total / HDL) • < 5:1 • Female < 4.4

  35. Triglycerides • normal < 200 mg/dL • women probably < 150 • borderline 200-400 • high 400-1000 • very high > 1000

  36. Lipid Panel • arcus • young patients • occlusive disease • optic neuropathy • xanthoma

  37. CASE #3

  38. Case #3 • 52 YOWM • CC: “inferior vision OS is dim” • MHx: diabetic x 20 years; poor control • VAs: OD 20/20 OS 20/20-2 • LEE: 6 month prior • two dot hemorrhages OD

  39. Initial Presentation • OD – unremarkable

  40. What is your tentative diagnosis? • 1. Anterior ischemic optic neuropathy • 2. Retrobulbar mass • 3. Papilledema • 4. Diabetic papillopathy • 5. Optic Neuritis • 6. Papillitis • 7. Other?

  41. What Should You Do?

  42. ESR • erythrocyte sedimentation rate • nonspecific test for inflammation • mm/hr • M: age/2 • F: (age+10)/2 • usually > 60 mm/hr in GCA

  43. C-Reactive Protein (CRP) • abnormal serum glycoprotein produced by liver during acute inflammation • disappears rapidly once inflammation subsides • 4 hour fast from food/fluids • alternative to ESR • more informative • ESR high in most elderly • no cross interference • normal: no CRP

  44. Causes of Optic Nerve Edema • Arteritic Ischemic Optic Neuropathy • Nonarteritic Ischemic Optic Neuropathy • Central Retinal Vein Occlusion • Compressive Optic Nerve Head Tumor • Diabetic Papillopathy • Infiltration of Optic Nerve Head • Malignant Hypertension • Papilledema • Papillitis • Papillophlebitis • Thyroid Ophthalmopathy

  45. Diabetic Papillopathy • 0.4 – 2% of diabetics • characteristics • sectoral or total ON edema • ± peripapillary hemorrhages • ± nerve fiber layer infarcts • ± macular edema • unilateral or bilateral • asymmetric

  46. Diabetic Papillopathy • retinopathy does not need to be present • small optic nerve cupping •  0.3/0.3 • usually associated with Type 1 DM? • prognosis: • signficant or complete recovery in several months • may have residual pallor and VF defect • pathophysiology is unclear

  47. Diabetic Papillopathy • Eye 2005 19:45-51 • 6 eyes • Betamethasone – Subtenons’ injection • duration decreased from 5 months to 3 weeks • Am J Ophth 2004 137(6) 1151-3 • 1 case – intravitreal triamcinolone • significant improvement in visual acuity

  48. CASE #4

  49. “Phone A Friend” • 40 YOBF • CC: “Decrease vision for 3 weeks” • HPI: OS worse than OD; no pain; acute • MHx: unremarkable • Meds: None • NKMA

  50. “Phone A Friend” • Entering Acuities • OD 20/60 PH 20/30 • OS 20/50 PH 20/30 • Refraction • OD • -2.00 –1.75 x 135 20/25 • -2.00 –5.00 x 167 20/50 • K readings… • OD 39.75 / 44.12 @ 095 • OS 36.75 / 43.50 @ 095 • Cornea • central corneal edema with “haziness”