The document reviews the genetics and pathophysiology of sickle cell anemia, detailing the distinction between normal adult hemoglobin (Hgb A) and sickle cell hemoglobin (Hgb S). It describes laboratory tests, including the sodium metabisulfite and dithionite tube tests, used to identify sickle cell traits and diseases, as well as the erythrocyte sedimentation rate (ESR) test's clinical relevance in inflammation assessment. Factors affecting ESR results are also discussed, such as the size and shape of red blood cells, highlighting the complexities of interpreting blood tests in sickle cell conditions.

1. Sickle Cell
1

2. Genetics Review
Chromosomes
Genes
Loci
Genotype
2

3. Normal Adult Hemoglobin (Hgb A)
 Heme molecule composed of iron in the
ferrous state (Fe++)
 Globin is the protein portion
 95-98% of adult Hgb is Hgb A
 Remaining amount is A2 and A3
3

4. Sickle Cell Hemoglobin (Hgb S)
 The amino acid glutamic acid is replaced by
amino acid valine
 Ability of RBCs oxygen carrying capability
is impaired
 Two possible genotype
– AS (sickle cell trait)
– SS (sickle cell disease)
4

5. Pathophysiology of Sickle Cell
 Sickle Cell trait
– Clinical manifestation
 Sickle Cell disease
– Clinical manifestation
5

6. Peripheral Blood Picture
 Varying number of sickled forms
 Marked anisocytosis, poikilocytosis,
and polychromasia
 Target cells, nucleated RBCs,
increased WBCs and platelets
 Reticulocyte count is elevated:
(5-25%)
6

7. Sodium metabisulfite
 Principle
– Cells containing Hgb S will “sickle”
when placed under a condition of
reduced oxygen tension
Sodium
Metabisulfate
15 minutes
&
30 minutes
7

8. Dithionite tube test
 Principle
– Hgb S is insoluble in a phosphate buffer
»Results in turbidity
– Hgb A is soluble
»Results in clear appearance
– Other abnormal hemoglobins
may result in turbidity
8

9. ESR Clinical Significance
• The ESR is a nonspecific test that
suggests the possibility of an inflammatory
process or tissue damage in the body
• The ESR is not diagnostic but is useful in
following the course of some diseases like
rheumatic fever, arthritis, and Lupus

10. Principle
 Based on principle of
sedimentation where solids settle
to the bottom of a liquid
 A known quantity of
anticoagulated blood is left
undisturbed, the RBCs separate
from the plasma and fall to the
bottom of the container

11. Procedure
 Anticoagulated blood is placed in a calibrated
tube of standard dimensions
 It is incubated in a vertical position and left
undisturbed for a designated period of time
(usually 1 hr)
 Distance RBCs fall within the given time is
measured in millimeters and reported
mm/hr

12. Types of ESR Methods
 Wintrobe – simplest and
mostcost effective
 Westergren – more sensitive
 Automated methods

13. Factors affecting ESR
Plasma factors
Abnormal plasma proteins
may lead to rouleaux
formation
(falsely increases ESR)
The single most important
factor in determining
ESR rate

14. RBC Factors
 Size
– Large erythrocytes settle faster than
smaller ones and will increase ESR
 Shape
– spherocytes settle rapidly while sickle cells
settle very slowly
 Number of RBCs
– In anemia there are less RBCs and more
plasma volume which increases ESR

15. Technical Factors
 Tilting
 Noise and vibration
 Temperature
 Test set up within 2hrs of blood collection
 ESR tube
 Well mixed sample
 Air bubbles
 Accurately timed