How and When to Order Blood Tests

1
How and When to Order Blood Tests

• Tammy Pifer Than, MS, OD, FAAO
• Carl Vinson VAMC
• Dublin, GA
• tammy.than_at_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 lt 7.0
• ask patients!

7
Fasting Plasma Glucose

• fluctuating vision
• get stable reading before new SpRx
• retinopathy
• diplopia
• vascular occlusions
• optic neuropathy

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CASE EXAMPLES
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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

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Subconjunctival Hemorrhage

• History
• frequency
• medications
• activity
• Examination

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Subconjunctival Hemorrhage

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

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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

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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 (Patients PT in seconds)ISI
  
• Mean normal PT in seconds
• ISI international sensitivity index
• Coumadin therapy

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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
• lt 35 seconds

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CBC with differential

• routine part of health care
• inexpensive
• screening
• anemia
• leukemia
• infection
• inflammation

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WBC (Part of CBC)

• Total
• overall number
• first line of defense
• decreased in aplastic anemia
• elevated in infections, leukemia

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WBC (Part of CBC)

• Differential
• 100 white blood cells
• of each
• neutrophils
• lymphocytes
• monocytes
• eosinophils basophils

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CBC

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

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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

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Fundus Whats Your Diagnosis?

• papilledema
• R/O mass
• R/O infection
• placing your bets...
• Idiopathic Intracranial Hypertension

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Workup

• CT or MRI
• unremarkable
• LP
• normal CSF content
• elevated pressure

24
Management

• weight loss
• acetazolamide
• Diamox?
• steroids??
• ON sheath decompression
• LP shunt

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Before you prescribe Diamox

• baseline electrolytes
• CBC with differential
• R/O blood dyscrasias
• monitor every 6 months

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Electrolytes

• Na
• 135.0 145.0 mmol/L
• K
• 3.60 5.00 mmol/L
• Cl-
• 101.0 111.0 mmol/L

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CO2 total content blood

• 21.0 31.0 mmol/L
• Increased
• alcoholism
• airway obstruction
• pneumonia
• drugs (e.g. antacids)
• Decreased
• dehydration
• Diamox
• measures compliance - lt 20 mEq/L
• tetracyclines

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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

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SMA-7

• Carbon dioxide
• Chloride
• Creatinine
• Glucose
• Potassium
• Sodium
• Urea nitrogen

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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 (HDLTriglycerides)/2
• HDL
• triglycerides
• risk for CAD
• ratio total cholesterol / HDL

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Cholesterol

• over half of adults in US have cholesterol gt 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 lt 130 mg/dL
• high ? 190 mg/dL
• Ratio (Total / HDL)
• lt 51
• Female lt 4.4

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Triglycerides

• normal lt 200 mg/dL
• women probably lt 150
• borderline 200-400
• high 400-1000
• very high gt 1000

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Lipid Panel

• arcus
• young patients
• occlusive disease
• optic neuropathy
• xanthoma

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CASE 3
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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

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Initial Presentation

• OD unremarkable

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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 (age10)/2
• usually gt 60 mm/hr in GCA

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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

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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

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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

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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 1945-51
• 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
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Phone A Friend

• 40 YOBF
• CC Decrease vision for 3 weeks
• HPI OS worse than OD no pain acute
• MHx unremarkable
• Meds None
• NKMA

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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 _at_ 095
• OS 36.75 / 43.50 _at_ 095
• Cornea
• central corneal edema with haziness

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Whats Your Tentative Diagnosis?

• 1. Keratoconus
• 2. Keratoconus with Acute Corneal Hydrops
• 3. Corneal Ulcer
• 4. Corneal Dystrophy / Corneal Degeneration
• 5. Dry Eye Syndrome
• 6. Herpes Simplex Keratitis
• 7. Other

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What Was Actually Done

• Cycloplegic
• Muro 128 qid
• RTC 1 day

53
Interstitial Keratitis

• cellular infiltration of the corneal stroma
• no primary involvement of epi or endo
• characterized by
• acute
• dense, white stromal necrosis
• vascularization (salmon patch of Hutchinson)
• later
• scarring and thinning
• ghost vessels

54
Interstitial Keratitis

• Syphilis (Congenital or Acquired)
• TB
• Lyme
• Parasitic infection
• HSV
• Sarcoidosis
• Leprosy
• Misc.

55
Syphilis Ever Had It?

• FTA-ABS
• fluorescent treponemal antibody absorption test
• ordered more frequently
• positive even after treatment
• MHA-TP
• microhemagglutination treponemal pallidum test

56
Syphilis Do you have it now?

• RPR
• rapid plasma reagin test
• VDRL
• venereal disease research laboratory test
• Treat If
• () RPR and ()FTA-ABS
• What if
• ()RPR and (-)FTA-ABS

57
PPD

• purified protein derivative
• TB skin test
• inject under skin
• check in 48-72 hours
• positive is gt10 mm wheal
• Positive for active and inactive TB

58
Lyme titer

• In endemic areas...
• Normal negative

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ACE

• angiotensin converting enzyme
• Enzyme found primarily in lung epithelial cells
• Some in blood vessels and renal tissue
• Converts angiotensin I to angiotensin II, a
  vasopressor that also stimulates adrenal cortex
  to produce aldosterone
• best for patients gt 20 YO
• helps confirm dx of sarcoidosis
• ACE elevated in 60

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Interstitial Keratitis

• Active
• 70 of unilateral ? Herpes Simplex Virus
• 60 of bilateral ? Idiopathic
• Inactive
• 50 of bilateral ? Syphilis
• All cases
• 20 attributed to syphilis