Drugs and Eosinophilia

Drugs, prescription and non-prescription,  and nutritional supplements are a common cause of eosinophilia across the world. In regions with a low prevalence of parasitic infestations drugs are the leading cause of eosinophilia.

Clinical Spectrum of Drug Induced Eosinophilia

The spectrum of drug induced eosinophilia extends from an asymptomatic eosinophilia discovered on a routine haemogram to a a serious disorder like drug induced drug reaction with eosinophilia and systemic syndromes (DRESS). Eosinophilia associated with specific organ complications includes

  1. Eosinophilic pulmonary infiltrates associated with the use of sulfadsalazine, nitrofurantoin and non-steroidal anti-inflammatory drugs (NSAID)
  2. Acute interstitial nephritis with eosinophilia  associated with the use of semisynthetic penicillins, cephalosporins, NSAID, sulphonamides, phenytoin, cimetidine and allopurinol
  3. Eosinophilia-myalgia syndrome (EMS) presents with increased eosinophil counts associated with  severe myalgia, neuropathy, skin rash and multi-system complications. The cause of EMS is not known but L-tryptophan has been implemented.
  4. Drug reaction with eosinophilia and systemic symptoms /Drug induced hypersensitivity syndrome (DRESS/DIHS): The syndrome is a form of delayed drug hypersensitivity the presents with fever lymphadenopathy and end organ damage. The spectrum of end-organ damage includes hepetitis, interstitial nephritis, pneumonitis and carditis. The drugs implicated in DRESS/DIHS include
    1. Anti-infective
      1. Antibiotics: Cephalosporins, doxycycline, fluoroquinolone, linezolid, metronidazole, nitrofurantoin, penicillins, tetracycline
      2. Sulfomaides: Sulfasalazine trimethoprim-sulfamethoxozole
      3. Sulfones: Dapsone
      4. Antiviral: Abacavir, Nevirapine
    2. Anti-epileptic: Carbamazepine, lamotrigine, phenobarbital, phenytoin, , valproate
    3. Anti-depressants: Amitriptyline, desimipramine, fluoxetine
    4. Anti-inflammatory: Diclofenac, ibuprofen, naproxen, piroxicam
    5. Antihypertensives: ACE inhibitors, β-blockers, hydrochlorthiazide
    6. Others:  Allopurinol, cyclosporine, ranitidine


The incriminating drug should be withdrawn in symptomatic patients. Asymptomatic eosinophilia does not necessitate discontinuation of therapy. If equally effective therapy is available it is preferable to stop therapy. If this is not the case the drug may be continued with careful monitoring for symptoms.

Hydroxyurea – Drug Information

Hydroxyurea was synthesised in Germany in 1860 and was found inhibit granulocyte production. It was only a hundred years after this that its potential as an anticancer drug was realized.

Hydroxyurea Mechanism of Action

Mechanism of Action of Hydroxyurea

Hydroxyurea enters the cell by passive diffusion. It inhibits of ribonucleotide reductase (RR). RR converts ribonucleotide diphosphates to deoxyribonucleotide diphosphates. Deoxyribonucleotide diphosphates are converted to deoxyribonucleotide triphosphates  and incorporated into DNA. Depletion of deoxyribonucleotide triphosphates results in impaired DNA synthesis. RR has two subunits M-1 and M2.  The M-2 subunit is the catalytic subunit and contains iron. Hydroxyurea inhibits RR by chelating iron. Hydroxyurea is an S phase specific drug. The cells exposed to hydroxyurea progress normally through the cell cycle, have a normal G1-S transition but accumulate in the S phase because of an inability to synthesise DNA. They then undergo apoptosis by p53 dependent and independent mechanisms.  Hydroxyurea may be transformed to nitric oxide. Nitric oxide is also an inhibitor of RR and may be responsible for drugs ability to induce foetal haemoglobin. This is important for treatment of sickle cell anaemia. Resistance to HU develops by elevated cellular activity of RR.

Pharmacokinetics of Hydroxyurea

Oral bioavailability of hydroxyurea is 80-100%. Parenteral formulation has no advantage over oral formulation. The drug is well distributed. It enters breast milk, cerebrospinal fluid and third space collections. The ratio of plasma to CSF levels is 4-9:1 and plasma to ascites levels is 2-7.5:1. The elimination half-life is 3.5-4.5 hours. Renal elimination is the main pathway of elimination. Sixty to eighty per cent of the dose eliminated by kidney unchanged. Patients with creatinine clearance of 10-50ml/hr should receive 50% and those with creatinine clearance of less than 10ml/hr should receive 20% of the planned dose. Hydroxyurea is metabolized but the metabolic pathways are not known.


  1. Myeloproliferative diseases
    1. Chronic myeloid leukaemia
    2. Essential thrombocytosis
    3. Polycythaemia Vera
  2. Acute leukaemia to control counts
  3. Sickle cell anaemia


Myelosuppression is the dose limiting effect of hydroxyurea. The dose of hydroxyurea needs to be titrated to the leucocyte and platelet counts. The acceptable lower limits of these counts will depend on the indication but generally speaking a leukocyte count less than 2.5X109/L or a platelet count less than 100X109/L is an indication for discontinuing therapy. With the abovementioned provisions in mind the dose of hydroxyurea for different indications are as follows:

  1. Myeloproliferative diseases: The usual dose is 20-30mg/kg/day.
  2. Acute leukaemia: 50-100mg/kg per day
  3. Sickle cell anaemia: 15-20mg/kg/day

Drug interactions

  1. HU inhibits formation of deoxynucleotides and enhanced the effect of agents damaging the DNA, as no nucleotides are available for repair. The effects of purine and pyrimidine analogues. When hydroxyurea is combined with any of these agents it should be done as a part of a protocol whose toxicity has been evaluated. This will prevent unacceptable toxicity.
  2. It has been shown to be synergistic with agents damaging the DNA like cisplatin, alkylating agents and topoisomerase II inhibitors.
  3. It has been used as a radiosensitizing agent in the treatment of head and neck and cervical cancer. It depletes the deoxynucleotide pool needed for DNA repair after radiation-induced damage.
  4. Enhanced anti HIV activity of azidothymidine, dideocytidine and dideoxyinosine


  1. Myelosuppression: The dose limiting toxicity of hydroxyurea is myelosuppression. Hydroxyurea causes rapid fall in leucocyte counts. When used in non-haematological malignancies the fall in leucocyte counts is evident by days 2-5. When used in patients with leukaemia the fall is evident faster, sometimes within a day. This property of hydroxyurea is useful in myeloid leukaemia with very high leucocyte count. Hydroxyurea is the treatment of choice for patients with chronic myeloid leukaemia presenting with very high counts. Though used in acute myeloid leukaemia with hyperleucocytosis, benefit from its use has not been proven in clinical trials.
  2. Gastrointestinal: Oral ulceration and gastrointestinal tract effects may be seen in some patients. They are particularly common in patients who receive chemoradiation with hydroxyurea.
  3. Skin: Dermatological changes may be seen with prolonged use. These include
    1. Skin Pigmentation and rash: Hyperpigmentation, erythema of the face and hands, diffuse maculopapular rash and dry skin. Severe reactions may resemble lichen planus.
    2. Nail Changes: The nails may show atrophy and formation of multiple pigmented bands.
    3. Leg Ulcers: Leg ulcerations may be seen in patients with prolonged therapy with hydroxyurea.
    4. Alopecia: Alopecia may occasionally be seen with the use of hydroxyurea
    5. Radiation Recall: Erythema or pigmentation of previously radiated skin may be seen in some patients.
  4. Mutagenicity and Teratogenicity: Hydroxyurea is a proven teratogen and contraindicated in women are pregnant or are planning a pregnancy. Women in the reproductive age group must be advised about contraception. The carcinogenic potential of hydroxyurea is uncertain. In view of the mechanism of action it is prudent not to use hydroxyurea for non-malignant disease.

Hyperleucocytosis and Leukostasis

Leukostasis is a oncological emergency seen in patients with leukaemia who present with pronounced leucocytosis. It is seen in about 5-30% of adult acute leukaemia cases. It results from slugging of microcirculation by leucocytes.  It is associated with a mortality of 20-40%.

Pathogenesis of Leukostasis

Manifestations of leukostasis result from impaired circulation in the affected vascular bed. Leukocytosis impairs circulation because of

  1. Increased viscosity
  2. Formation of intravascular leukocyte aggregates (white bland thrombi)
  3. Increased adhesion of blasts to the endothelium

Cells increase the viscosity of blood hampering flow through microcirculation. Pliability of blood cells is important for maintaining blood flow in microvasculature. The biconcave shape of the erythrocytes provides them with deformability allowing smooth passage through the microvasculature. Leukocytes are less pliable than erythrocytes.  Normally the number of leucocytes is a small fraction of the number of erythrocytes. The contribution of leucocytes to blood viscosity in minimal.

Blood viscosity increases with leucocytosis. The increase is related to the leucocyte count, size of the leukocytes and the deformability of the leucocytes. Blasts are less deformable than mature cells. Myeloblasts are larger and less deformable than lymphoblasts. Cells of the monoblastic series are the least deformable. Lymphocytes are the smallest and have the least impact on the viscosity amongst all leucocytes.

Blasts secrete cytokines like IL-1β  and TNF-β. These lead to up regulation of adhesion molecules like ICAM-1, VCAM-1 and E-selectin that increases the adhesion of blasts to the endothelium. Adhesions of blasts to microvasculature further diminish blood flow.

The vascular beds most commonly affected are the lung, CNS and the eye. Tissue hypoxia resulting from impaired circulation is believed to contribute to elevated LDH seen in acute leukaemias. 

Clinical Features

About 5-13% of acute myeloid leukaemia and 10-30% of acute lymphoblastic leukaemia have hyperleukocytosis. The symptoms of leukostasis are related to the ischaemia in the affected circulatory bed. The commonest vascular beds affected and the symptoms attributable to these beds are listed below.

Organ Manifestation
Brain Stupor
Eyes Blurring of vision
Lungs Dyspnoea
Kidney Azoaemia
Heart Arrhythmia
Penis Priapsim

Examination of the fundus shows papilledema, blurred disc margins, dilated blood vessels, and retinal haemorrhages.

The leukocyte count  at which symptoms develop depends on the type of leukaemia. Symptoms develop at the lowest counts in acute myeloid leukaemia. Patients of chronic lymphocytic leukaemia may not have symptoms of hyperleukocytosis at leucocyte counts as high as 400X109/L. Leukostasis is associated with increased morbidity and mortality.


Leukostasis is clinical diagnosis of exclusion. It should be considered in any patients with lung or CNS symptoms who has hyperleukocyosis. Hyperleukocytosis has been variably defined as a count of 50X109/L or 100X109/L. Symptoms are likely to occur at lower counts in patients with acute myeloblastic leukaemia particularly when there is a monocytoid component. Patients with chronic lymphoblastic leukaemia tolerate counts as high as 400X109/L without symptoms. The conditions that can mimic leukostasis include

  1. Pulmonary infection
  2. Pulmonary embolism
  3. Pulmonary oedema
  4. Pulmonary haemorrhage
  5. Transfusion-related acute lung injury  is blood products have been transfused
  6. CNS infections – meningitis and encephalitis
  7. Conditions causing acute mental status change

The x-ray findings include diffuse interstitial or alveolar infiltrates. It can be normal in early stages. Examination of the fundus is important.


Leukostasis is associated with a mortality of 20-40%. The treatment of leukostatsis is to rapidly reduce the leukocyte count. Three methods of rapidly reducing leucocyte counts are induction chemotherapy, leukocytopheresis or low dose chemotherapy. Each of these methods are supported by theoretical arguments. Induction chemotherapy is the definitive therapy for leukaemia. Whether leukocytopheresis or hydroxyurea add to the benefit of induction chemotherapy is not clear. The use of hydroxyurea and leukocytopheresis is dictated by the experience of the treating centre. The procedures are usually resorted to with the belief that induction therapy with a very high leucocyte count may increase the risk of tumour lysis. 

Leukocytopheresis: Leukocytopheresis is used because it rapidly brings down the leucocyte count without causing lysis of blasts. It has the theoretical advantage of reducing the risk of tumour lysis and reducing mortality. This has never been proven in clinical trials. Two procedures needed about 12-24 hour apart. Leukocytopheresis is indicated in

  1. Symptomatic patients with AML with leucocyte counts more than 50X109/L and ALL with counts more than 150X109/L.
  2. Asymptomatic patients with AML and leucocyte  counts >100 X 109/L
  3. Asymptomatic patients with ALL with leucocyte counts >300 X 109/L
  4. CML patients who are symptomatic with leucocyte counts greater than 150X109/L,
  5. CLL patients who are symptomatic with leucocyte counts greater than 500X109/L. 
  6. It should not be performed in patients with acute promyelocytic leukaemia symptomatic or asymtomatic

The procedure involves insertion of a catheter. This may be associated with an increased risk of bleeding as these patients have thrombocytopenia.

Low Dose Chemotherapy: Like leukocytopheresis the value of low dose chemotherapy has not been proven. The following interventions may be used (with leukocytopheresis)

  1. Acute myeloid leukaemia should be treated with hydroxyurea in a dose of 50-100mg/Kg. It may be administered as a single or multiple doses.
  2. Acute lymphoblastic leukaemia may be treated with steroids with or without vincristine. 

Induction chemotherapy: Induction chemotherapy is the definitive therapy for acute leukaemia. High counts are associated with a higher risk of tumour lysis resulting in an apprehensions of starting chemotherapy in patients with very high leucocyte counts.

Other measures: Cranial irradiation and dexamethasone has been used in patients with CNS symptoms. Blood transfusions can increase viscosity and may worsen symptoms of leukostasis. One needs to be conservative about red cell transfusions till the leukocyte counts become normal. Transfusions in patients with symptoms attributable to anaemia should not be held back. 


Leukaemia – The Peripheral Smear

Differentiating Acute and Chronic Leukaemia

Leucocytosis with anaemia is a feature of acute and chronic leukaemia. It is possible to differentiate acute and chronic leukaemia by looking at the peripheral smear. Patients with acute leukaemia often have thrombocytopenia. Patients with chronic lymphocytic leukaemia may have normal or low platelet counts. Patients with chronic myeloid leukaemia have normal or high platelet counts.

Haemoglobin Platelets Peripheral Smear
Acute Leukaemia Low Low Immature forms other than blasts not seen
Chronic Lymphocytic Leukaemia Low or Normal Low or Normal Normal looking lymphocytes
Chronic Myeloid Leukaemia Low or Normal Normal or High Immature leucocytes, all phases of leucocyte maturation seen

The phases of maturation of myeloid cells (from the least to the msot mature) are blasts, promyelocytes, myelocytes, metamyelocytes, band form and mature granulocyte (see Myeloid Precursors Morphlogy). The peripheral smear from patients with acute leukaemia shows blasts (or promyelocytes) and mature neutrophils. Very few cells, if any, with maturity between the two stages that occupy two ends of the spectrum are seen. Patients with with chronic myeloid leukaemia have cells with all stages of maturity between blasts and mature granulocytes. The peripheral smear in patients with acute leukaemia shows mature lymphocytes.

The explanation for the different peripheral smear findings in acute leukaemia and chronic myeloid leukaemia is in the pathogenesis of the two diseases. Chronic myeloid is a myeloprolferative disease. It is a clonal disease. The stem cells of patients with chronic myeloid leukaemia carry the BCR-ABL mutation. This mutation results in clonal expansion. All blood cells in a patient arise from one clone. The release of cells from the bone marrow of patients with CML is not limited to mature granulocytes. Some cells leave the marrow and result in leucocytosis.

The marrow of a patient of acute leukaemia has two clone one malignant one normal. The malignant clone can not differentiate beyond the stage of a blast (or promyelocyte). It slowly effaces the normal clone. The mature granulocytes seen in the peripheral smear arise from the normal clone and the blasts from the malignant clone. The normal clone releases cells only when they mature to the stage of band cell or beyond. The malignant clone can not mature beyond the stage of a blast. The stages between blasts and band forms/mature granulocytes are not seen in peripheral smear of acute leukaemia.

Large Granular Lymphocyte

Typically lymphocytes are small (10-12μm) cells with a scanty agranular cytoplasm with a round slightly indented nucleus. About 10% of lymphocytes are larger (12-16μ), have a nucleus which has a slight less compact chromatin and azurophilic granules in the cytoplasm. These are known as large granular lymphocytes. Some of these are T supressor lymphocytes (Cd3+ Cd8+) while others are NK cells (Cd3 – CD8+). The picture above shows a large granular lymphocyte.

Determinants of Blood Viscosity

Fluids flow on application of pressure. The flow may be laminar flow that is orderly in parallel layers or turbulent flow that is chaotic. During laminar flow the layer closest to the wall is the slowest and the layer farthest, fastest. Viscosity, the internal friction between these layers, is a measure of thickness of a fluid. The higher the viscosity, thicker the fluid. Depending on whether the viscosity of fluids changes with flow rate or not fluids may be Newtonian of non-Newtonian. The viscosity of Newtonian fluids like water, honey and oil does not change with flow rates. The viscosity of blood, a non-Newtonian fluid, Blood viscosity increases with falling shear rates. The increase is dramatic at low shear rates. Blood viscosity depends on plasma viscosity and the type and number if blood cells.

Determinants of plasma viscosity

Plasma viscosity varies with the concentration of its constituents.  Fibrous proteins like fibrinogen contribute more to plasma viscosity than globular proteins like albumin. Acute phase reactants increase plasma viscosity. Of the plasma constituents immunoglobulins and cholesterol are clinically relevant. Clinically significant increases in viscosity are most common in patients with increased immunoglobulin, both monoclonal and polyclonal. The commonest cause of hyperviscosity syndrome is increased IgM in patients with of Waldenström’s macroglobulinaemia. Patients with IgG3 and IgA multiple myeloma, cryoglobulinemia, both monoclonal and polyclonal and patients with polyclonal gammopathies may have hyperviscosity. Very high cholesterol levels in patients with primary biliary cirrhosis have also been associated with hyperviscosity. Plasma viscosity decreases with temperature.

Effect of Number and Type of Cells on Viscosity

Haematocrit and cell deformity affect blood viscosity.  Blood viscosity increases with haematocrit in an exponential manner. There is a pronounced increase in viscosity at haematocrits more than 55%.

Blood cells disrupt flow lines of plasma and increase viscosity. Erythrocytes are the most numerous and under physiological conditions the flow properties of blood depend on the properties of plasma and erythrocytes. The normal erythrocyte is a biconcave disk about 7.8 µm in diameter (figure 1). At low flow rates erythrocytes aggregate in the form of stacks known as rouleaux. These large aggregates cause a sharp increase in viscosity. With increasing flow rates the shear stress on the erythrocyte rouleaux increases causing the erythrocytes to disaggregate. Disaggregation reduces viscosity. Any reduction in viscosity after complete disruption of rouleaux depends on the capacity of the erythrocyte to change so that resistance offered to flow decreases. The erythrocyte may take a bullet, parachute or a slipper form (figure 1). The deformability needed for shape change depends on the amount of surplus membrane, the properties of membrane and the viscous properties of the erythrocyte cytoplasm.  RBC deformability is decreased in patients with hereditary spherocytosis because of decreased amount of membrane and in sickle cell anaemia because altered viscosity of haemoglobin and membrane damage. Malaria is characterized by deceased deformability and increased adhesiveness. Increased viscosity is responsible clinical manifestations of sickle cell anaemia and malaria. Intracellular crystallization of haemoglobin causes increased viscosity in haemoglobin C disease.

Erythrocytes change shape with increasing flow rate

Figure 1. Deformability and aggregation of erythrocytes is responsible for changes in viscosity of blood as the flow rate increases. The normally biconcave erythrocyte aggregate into rouleaux at low flow rates. As the shear stress increases because of increased flow, the rouleaux disaggregate. Further increase in viscosity results in change in shape of the erythrocyte from biconcave to bullet shaped, parachute shapes and slipper shaped forms. These shapes offer less resistance to floe than the biconcave forms. Erythrocytes have about 40% surplus membrane. This surplus is important for shape change. Erythrocyes with viscous cytoplasm (HbS and HbC) resist change in shape increasing viscosity of blood in these diseases.

Leukocytes are larger than erythrocytes. As opposed to an erythrocyte volume of 80-90 (femtoliter) fL, the volume of a leukemic lymphocyte is 190-250 fL, lymphoblast is 250-350 fL and myeloblast is 350-450 fL.  Viscosity depends on haematocrit. The contribution of leucocytes to normal haematocrit is small (~1.2%). Under physiological conditions haematocrit is practically equal to erythrocrit.  Leucocytes are larger and less deformable because of the presence of a rigid nucleus. For a similar increase in count the leukocrit rises more than erythrocrit. Acute leukaemia is characterized by progressively increasing anaemia as the leukocyte counts increase. As the increased leukocrit is more than offset by anaemia in almost all patients with acute leukaemia, hyperviscosity is rare in acute leukaemias. There is an inverse relationship between leukocrit and erythrocrit in leukaemias for leukocrit values less than 15% for chronic leukaemias. The lymphocytes of chronic lymphocytic leukaemia are small and counts needed for a pathological increase haematocrit are rarely reached. Anaemia in patients of chronic myeloid leukaemia is less severe than acute leukaemia. Myeloid cells are larger than lymphoid cells.  This makes patients with CML at the greatest risk for hyperviscosity. Anaemia is leukaemia protects from hyperviscosity. This must be borne in mind before initiating red cell transfusions in leukaemia patients.


  1. Blood rheology and hemodynamics. Baskurt OK, Meiselman HJ. Semin Thromb Hemost. 2003 Oct;29(5):435-50.
  2. Oguz K. Baskurt. Max R. Hardeman. Michael W. Rampling and Herbert J. Meiselman. Handbook of Hemorheology and Hemodynamics. 2007. IOS press. ISBN 978-1-58603-771-0 [Preview at Google Books

Neutrophil Segmentation and Projections

The neutrophil nucleus is segmented. The nucleus of the most immature neutrophil, band neutrophil lacks segmentation. It differs from a metamyelocyte in that the concave and convex surfaces of the nucleus are parallel. It may be coiled as is the case of the cell next to the basophil in figure 1.

The Arneth believed that the number of lobes increase as the neutrophil ages. This is not entirely true. The number of lobes in a neutrophil nucleus is decided at the band stage or earlier. After release the neutrophil nuclear segmentation may continue till the cell achieves the number of lobes it is programmed to reach. A cell that is programmed to become a three lobed neutrophil and a cell that is programmed to become a five lobed neutrophil both start as band forms but segmentation in the former stops at three lobes. The average number of neutophil lobes in a normal peripheral smear is 2.5-3.3. The definition of lobes differs from observer to observer (figure 2 and 3)

Infection and inflammation result in increased neutrophil production. Young neutrophils have fewer lobes and the average neutrophil lobulation decreases (shift to left, smaller numbers occupy a left position on the X axis of a graph). Other inflammatory changes including leucocytosis, toxic granules, Döhle bodies and neutrophil vacuolation may also be seen in patients showing “shift to left” because of infection/inflammation. Patients with chronic myeloid leukaemia (CML) and other myeloproliferative diseases or myelodysplastic/myeloproliferative disease (MDS/MPD) also show a shift to left but it is usually possible to differentiate these conditions from infection/inflammation. Peripheral smear of patients of CML (typical and atypical) and chronic myelomonocytic leukaemia show the entire spectrum of myeloid cells (myeloblasts, promyelocytes, myelocytes, metamyelocytes, band forms and segmented neutrophils). CML shows more than 10% immature forms and without monocytosis. Chronic myelomonocytic leukaemia usually shows less than 10% immature forms and shows an absolute monocyte count more than 1 X 109/L. The BCR-ABL translocation can be detected in patients with CML, but not in atypical CML. Band forms and cells with few nuclear segments dominate the peripheral smear in infection/inflammation. An occasional myelocyte or metamyelocyte may be seen. A promyelocyte or myeloblast is almost never seen. When these cells are seen in seen in substantial numbers a diagnosis of MDS/MPD should be considered.

In women one of the X chromosomes is inactivated and appears as the drumstick appendage. It is seen in 0.5-2.6% of the neutrophils. The prevalence of the drumstick increases with segmentation of the nucleus.

The exact mechanism and purpose of segmentation of the granulocyte nucleus is not known. It may aid in making the cell more deformable and allow it to squeeze from the vessels into the tissue. It is rare to find a neutrophil with more than five nuclear lobes. Increased nuclear lobulation is a feature of megaloblastic anaemia, iron deficiency anaemia (Br J Haematol 107:512;1999), uraemia, infection, myelodysplastic syndromes and hereditary neutrophil hypersegmentations. Hypersegmentation increases the average neutrophil lobe count and hence the term shift to right. A ratio of five lobed to four lobed neutrophil of 17% or more is the most sensitive indicator of shift to right. Hypersegmentation due to megaloblastic anaemia recovers in about two weeks after initiation of therapy (Ann Intern Med 90:757). Hypersegmentation can be used for diagnosis in patients who have been empirically treated with vitamin B12 and/or folate as other disease related changes rapidly revert to normal. Macropolycytes are large neutrophils often with a hypersegmented nucleus. They are tetraploid (have 96 chromosomes instead of 48 chromosomes). Hypersegmentation in macropolycytes reflects increased DNA.