Diagnostic Blood Tests

1
Diagnostic Blood Tests

• And their meaning

January 14th, 2009 Annie Yeung, Ivy Woo, Jia-Wei
Yuen, Sylvie Lam
2
Why tests are ordered?

• TWO major reasons why physicians order tests
• For diagnosis of disease or condition
• For management of illness or health

3
Purposes

• Diagnostic Testing
• To confirm a condition that there is some
  evidence for
• To exclude a disease that is possible but not
  likely
• To screen for disease without symptoms
• To determine risk factors for disease

4
Purposes

• Management Testing
• To monitor the treatment of a disease
• To follow the course of the disease
• To predict what is likely to happen to the
  patient (prognosis)

5
Other reasons for testing

• For curiosity
• To be seen to be doing something
• To practice scientific medicine
• To follow tradition
• To avoid litigation
• To make money

6
Factors to consider with each test

• Pre-analytical
• Analytical
• Post-analytical

7
Pre-analytical factors

• That are of greatest concern to the patients
• ALL health care providers should know them in
  order to advise the patient and the laboratory
  staff if
• the patient is not prepared according to
  instructions OR
• has a condition that may affect testing
• Examples
• Diet
• Drugs
• Sex

8
Analytical factors

• Responsibility of laboratory professionals
• Example
• Sodium
• Flame photometry or colorimetrically
• The results are not the same on all specimens
• Measure sodium concentration or ion activity
• Uncertainty of lab tests
• NOT the best methods but are CHEAP!!!
• Give the results quickly and on small samples

9
Post-analytical factors

• Responsibility of physicians and other health
  care providers including pharmacists
• Help you to differentiate between healthy or sick
  population
• Assess if the patient is getting worse or better
• Clinical sensitivity the ability of a test to
  detect a disease when the disease is present
• Clinical specificity the ability to detect the
  absence of disease when no disease is present

10
Blood Test Topics

• Complete Cell Count (CBC)
• Red Blood Cell (RBC)
• Hemoglobin (Hb)
• Hematocrit (Hct)
• Red Blood Cell Indexes
• White Blood Cells (WBC)
• Platelet Count
• Pregnancy Test

11
Complete Blood Count

• A screening test performed on peripheral blood
• Most commonly performed test as part of a
  general check up
• Samples are inserted into automated analyzer

12
Red Blood Cells (RBC)

• A number count of circulating RBC in 1mm3 of
  peripheral blood
• Normal 106/µl or 1012/L
• Adults/ Elderly
• Male 4.7 6.1
• Female 4.2-5.4
• Children
• Newborn 4.8-7.1
• 6-18 years 4.0-5.5

13
What does it mean?
14
White Blood Cells (WBC)

• 2 components Total WBC and Differential Count
• Normal Values
• Total WBC
• Adult/ child gt2 years 5000-10000/mm3
• Child lt or 2 years 6200 17000/mm3
• Newborn 9000-30000/mm3
• Differential Count
• Neutrophils 55-70
• Lymphocytes 20-40
• Monocytes 2-8
• Eosinophils 1-4
• Basophils 0.5-1

15
WBC continued

• DRUGS that increase WBC allopurinol, aspirin,
  chloroform, epinephrine, heparin, quinine,
  steroids triamterene
• DRUGS that decrease WBC AB, anticonvulsants,
  antihistamines, antimetabolites, antithyroid
  drugs, arsenicals, barbiturates, chemotherapeutic
  agents, diuretics and sulfonamides

16
Pregnancy Test

• Human Chorionic Gonadotropin (hCG) is produced by
  syncytiotrophoblast that surrounds the blastocyte
• hCG appears in blood and urine as early as 10
  days after conception
• Methods employing use of antibodies target the
  beta subunit (specific to hCG)
• Immunologic Urine test
• Radioimmunologic Serum sample, highly sensitive

17
Why is a Blood Test recommended if pregnancy is
suspected?

• Commercially available urine tests may give
  inaccurate results due to
• dilute urine (false-negative)
• hematuria / proteinuria (false-positive)
• Urine test results may be affected by certain
  drugs
• Diuretics (false-negative)
• Anticonvulsants, antiparkinsonian drugs
  (false-positive)
• Lack of quantitative values to help identify
  potential ectopic pregnancy, hydatidiform mole of
  uterus, choriocarcinoma

18
Pregnancy Test continued

• Normal Values
• Males and Non-pregnant females lt5
• On the other hand

19
www.mercksource.com
20
Summary

• There are a wide variety of blood tests available
  to help Physicians diagnose and monitor a
  patients condition
• Pre-analytical, analytical, post-analytical
  factors must be considered to ensure a test
  performed is suitable, effective, and the results
  meaningful.
• Complete Blood Count (CBC) is commonly ordered
  during a physical check-up.
• CBC provides a baseline profile for a healthy
  individual. Abnormal values may suggest the need
  for intervention. For example, CBC is helpful for
  the diagnosis of anemia.
• Take home urine tests for pregnancy is less
  informative than the blood test. Due to the need
  for medical attention, refer patient to the
  Doctor.
• Blood pregnancy tests provide valuable
  quantitative information that allow early
  recognition of conception/abnormal states .
• Ensures prompt and proper care of the patient
• Allows time for decision making

21
References

• http//www.cartoonstock.com/default.asp
• http//www.labtestsonline.org/understanding/analyt
  es/cbc/test.html
• http//www.mdsdx.com/Lifelabs_ON/Patients/TestInfo
  /LabTestGlobal.asp
• http//www.merck.com/mmhe/appendixes/ap2/ap2b.html
  
• http//www.mercksource.com/pp/us/cns/cns_hl_dorlan
  ds_split.jsp?pg/ppdocs/us/common/dorlands/dorland
  /seven/000086098.htm
• http//www.nlm.nih.gov/medlineplus/laboratorytests
  .html
• Fu, Lei, and Kavsak, Pete. "Why laboratory tests
  are ordered." Series
• Introduction to Biochemistry of Human Disease.
  University of Toronto. Toronto, 2006.
• Ganong, William F. (2005). Review of Medical
  Physiology (22nd ed.) The McGraw-Hill Companies,
  Inc.
• Pagana, Katheleen D. and Timothy J. Pagana.
  (2007). Mosbys Diagnostic and Laboratory Test
  Reference (8th ed.). Elsevier Inc.