Discussion
CBC is the most commonly ordered test in hospitalized patients. Modern
automated blood cell counters produce a detailed report on the red
cells, white cells and platelet, with differential white blood cell
counts. A drop of the remaining blood could then be smeared and stained
(4). Microscopic examination of this smear under expert eye yields
useful information and further details regarding all formed elements of
the blood (5). “More information can be gained from examining the blood
smear than from any other single hematologic procedure”, Jandl in 1987
said (6). This shows the value of PBS review in the medical management.
Initiation of a PBS review depends on the laboratory policy. It could be
a clinical request by the attending clinician on the account of a
clinical suspicion or initiated by the laboratory due to clinical
information, numerical deviations in the automated counts, flags raised
by the analyzers or based on a designed protocol in the laboratory(based
on workload of the laboratory) (4, 7). For certain disorders, for
instance hematologic malignancies or parasitic infestations, examination
of the PBS can be diagnostic. For others such as our case, the PBS
provides important clues in the clinical management and determines which
diagnostic tests are indicated (2).
Among all useful data obtained from the blood smear, there is valuable
information about the red blood cell size, shape, staining (color) and
intracellular inclusions. Red cell inclusions often result from
defective maturation of the erythrocytes, oxidant injury to the cells or
infections and are almost always indicative of some sort of pathology.
Basophilic stipplings (punctuate basophilia) are well-known red cell
inclusions. In fact they are denatured RNA fragments dispersed within
the cytoplasm (7). They are present as irregular basophilic granules
which stain deep blue with Wright’s stain. They vary from fine to
coarse. Fine stippling is commonly seen with increased production of the
red cells. Coarse stippling may be seen in haemoglobinopathies
(thalassemias), sideroblastic anemia, megaloblastic anemia, and a rare
inherited condition, pyrimidine 5’ nucleotidase deficiency.
Sideroblastic anemia is characterized by accumulation of iron in the
mitochondria, which appears as ring distribution around the nucleus of
the erythroid precursors on iron stain. Sideroblastic anemia occurs as
primary or secondary (5,7).
Lead poisoning is an important cause of secondary sideroblastic anemia
because environmental exposure to lead is usually unrecognized and needs
to be detected (5). Lead exposure usually occurs through contaminated
air and food. Excess lead affects almost every organ in the body. The
major anatomic targets are the blood (bone marrow), nervous system,
gastrointestinal tract, and kidneys. Lead has a high affinity for
sulfhydryl groups and interferes with the enzymes involved in heme
synthesis. Iron incorporation into heme is impaired, leading to
microcytic hypochromic anemia with distinctive punctate basophilic
stippling of the red cells. Lead also inhibits sodium- and
potassium-dependent ATPases in the cell membranes, an effect that may
increase the fragility of red cells, causing hemolytic anemia (8).
The classic form of lead neuropathy consists of weakness that primarily
involves the wrist and finger extensor (wristdrop and footdrop). Excess
lead could induce “lead lines” formation in epiphyses of the bone and
gum. The gastrointestinal tract is also a locus for major clinical
manifestations. Lead ”colic” is characterized by extremely severe,
poorly localized abdominal pain and finally since the excretion of lead
occurs through the kidneys, exposures may cause damage to the proximal
tubules, interstitial fibrosis and possibly renal failure(8).
Since lead poisoning is a condition with potential multiorgan damage, it
can be traced in the human body with variable laboratory tests. The
half-life of lead in the blood and bone is 35 days and 32 years,
respectively, so the blood lead level just reflects the current and
recent exposure (5, 9). Table 2 shows different laboratory tests, their
properties and changes in cases of lead poisoning. Elevated blood lead
(> 10 µ/dL) and red cell free protoporphyrin levels
(> 50 µg/ dL) or, alternatively, zinc-protoporphyrin
levels, are required for definitive diagnosis (5).