How and When to Order Blood Tests

Tammy Pifer Than, MS, OD, FAAOCarl Vinson VAMC

Dublin, GA

tammy.than@va.gov

Getting the Job Done...

• PCP

• External laboratory

• In-office sampling is it ok?

Before You Order Tests...

• good case hx

• narrow ddx

• avoid “shot gun” approach

• comprehensive ocular exam

If You Order Tests...

• interpret Laboratory Tests and Diagnostic Procedures

4th edition - 2004 Chernecky and Berger

– includes Herbal interactionsincludes Herbal interactions ISBN 0721603882 $41.95

• communicate• treat• refer

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!

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!

Fasting Plasma Glucose

• fluctuating vision get stable reading before new SpRx

• retinopathy

• diplopia

• vascular occlusions

• optic neuropathy

CASE EXAMPLES

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

Subconjunctival Hemorrhage

• History frequency medications activity

• Examination

Subconjunctival Hemorrhage

• Blood pressure

• CBC with differential

• PT (prothrombin time)

• PTT (partial thromboplastin time) or APTT (activated PTT)

• INR (international normalized ratio)

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

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

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

CBC with differential

• routine part of health care

• inexpensive

• screening: anemia leukemia infection inflammation

WBC (Part of CBC)

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

WBC (Part of CBC)

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

CBC

• RBC count• hemoglobin• morphology• hematocrit

volume of RBC in 100 mL 3 x Hgb

• platelets

Coagulation Studies

• recurrent subconjunctival hemorrhages

• non-traumatic hyphema

• artery or vein occlusion

• pre-op cataract surgery?

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

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

Fundus: What’s Your Diagnosis?

• papilledema

• R/O mass

• R/O infection

• placing your bets... Idiopathic Intracranial Hypertension

Workup

• CT or MRI unremarkable

• LP normal CSF content elevated pressure

Management

• weight loss

• acetazolamide Diamox

• steroids??

• ON sheath decompression

• LP shunt

Before you prescribe Diamox

• baseline electrolytes

• CBC with differential R/O blood dyscrasias

• monitor every 6 months

Electrolytes• Na+

135.0 – 145.0 mmol/L

• K+

3.60 – 5.00 mmol/L

• Cl-

101.0 – 111.0 mmol/L

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

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

SMA-7

Carbon dioxide Chloride Creatinine Glucose Potassium Sodium Urea nitrogen

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

• Also SMA-20

Eyelid Xanthoma• dermis infiltrated with xanthoma cells

• yellow bilateral plaque

• medial aspect UL

• management: cautery laser anything else?

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

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

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

Triglycerides

• normal < 200 mg/dL women probably < 150

• borderline 200-400

• high 400-1000

• very high > 1000

Lipid Panel• arcus

young patients

• occlusive disease

• optic neuropathy

• xanthoma

CASE #3

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

Initial Presentation• OD – unremarkable

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?

What Should You Do?

ESR

• erythrocyte sedimentation rate

• nonspecific test for inflammation

• mm/hr

• M: age/2

• F: (age+10)/2

• usually > 60 mm/hr in GCA

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

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

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

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

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

CASE #4

“Phone A Friend”

• 40 YOBF

• CC: “Decrease vision for 3 weeks”

• HPI: OS worse than OD; no pain; acute

• MHx: unremarkable

• Meds: None

• NKMA

“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”

What’s 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

What Was Actually Done…

• Cycloplegic

• Muro 128 qid

• RTC 1 day

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

Interstitial Keratitis

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

Syphilis: Ever Had It?

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

• MHA-TP microhemagglutination treponemal pallidum test

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

PPD

• purified protein derivative

• TB skin test

• inject under skin

• check in 48-72 hours

• positive is >10 mm wheal

• Positive for active and inactive TB

Lyme titer

• In endemic areas...

• Normal: negative

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 > 20 YO• helps confirm dx of sarcoidosis

ACE elevated in 60%

Interstitial Keratitis

• Active 70% of unilateral Herpes Simplex Virus 60% of bilateral Idiopathic

• Inactive 50% of bilateral Syphilis

• All cases 20% attributed to syphilis