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).