13. INTRODUCTION TO PATHOLOGY OF BLOOD AND URINE

PATHOLOGY OF BLOOD AND URINE: A TEACHER’S COMPREHENSIVE GUIDE

Welcome, future pharmacists and healthcare professionals!

The word pathology has been derived from two Greek words, i.e., pathos meaning experience or suffering, and logia meaning study of; thus a branch of medical science which diagnoses disease on the basis of the laboratory analysis of body fluids (blood and urine) and tissues, by using the tools of chemistry, clinical microbiology, haematology, and molecular pathology is known as pathology.

Dpharmguru’s exam insights:

In my years of teaching pathology, I have observed that students often get confused between haematology and pathology. Remember: Haematology is the study of blood and blood disorders, while pathology is the broader study of disease diagnosis through laboratory analysis of body fluids and tissues. This distinction is frequently tested in exams!

PART 1: PATHOLOGY OF BLOOD

Blood is a connective tissue that plays a vital role in carrying out various life processes, and protects the body against diseases. Blood is a unique component for every individual as it differs in composition, number of cells of each type and its functions, from one individual to another. Haematology is the branch of medical science concerned with the study of blood, blood-forming tissues, and blood disorders.

Composition of Blood

Around 8% of total body weight is blood (adult female, 4-5 litres and adult male, 5-6 litres). Blood is a connective tissue, having a liquid matrix with cells and cell fragments. Two major components of blood are:

• Blood plasma, a clear extracellular fluid
• Formed elements, composed of blood cells and platelets

Normal Range of Blood Components

Blood Component	Normal Range
RBC (Men)	4.32-5.72 million cells/mcL
RBC (Women)	3.90-5.03 million cells/mcL
Haemoglobin (Men)	135-175 g/L
Haemoglobin (Women)	120-155 g/L
Haematocrit (Men)	38.8-50.0%
Haematocrit (Women)	34.9-44.5%
WBC	3,500 to 10,500 cells/mcL
Platelet Count	150,000 to 450,000/mcL

Functions of Blood

• Transportation: Transports O₂ and CO₂ to the body cells with the help of RBCs.
• Thermoregulation: Acts as a thermoregulator as body transfers heat during blood circulation.
• Hydraulic Functions: Restriction of blood flow can cause engorgement of tissues.
• Act as a Vehicle: Carries hormones, vitamins and other essential chemicals.
• Maintenance of Ion Balance: Maintains ionic balance between the intercellular spaces.
• Regulation of Water Balance: Actively involved in the regulation of water content of the body.
• Regulation of Acid-Base Balance: Plasma proteins and haemoglobin act as buffers.
• Regulation of Body Temperature: Maintains homeostasis via thermoregulatory mechanism.
• Storage Function: Functions as reservoir of water and other substances.
• Defensive Function: WBCs protect body against bacteria or antigens by engulfing them.

Lymphocytes

Lymphocytes are a type of white blood cells which are part of the immune system. These white blood cells are colourless cells formed in lymphoid tissue, hence referred to as lymphocytes. They are commonly known as natural killer cells. These are small and slightly spherical with large round nucleus and constitute 20-40% of leukocytes or white blood cells.

There are two main types of lymphocytes:

• B Lymphocytes (B Cells): These cells produce antibodies which are used to attack invading bacteria, viruses, and toxins.
• T Lymphocytes (T Cells): These cells destroy the body’s own cells that have themselves been taken over by viruses or have become cancerous.

Dpharmguru’s exam insights:

Remember: B cells produce antibodies (humoral immunity), while T cells directly attack infected or cancerous cells (cell-mediated immunity). This is a very common exam question! Also, lymphocytes make up 20-40% of total WBCs.

Lymphocytosis and Lymphocytopenia

Lymphocytosis: High levels of lymphocytes in blood. Causes include hepatitis, syphilis, mononucleosis, tuberculosis, HIV/AIDS, hypothyroidism, infections, and blood cancers.

Lymphocytopenia: Low levels of lymphocytes in blood. Causes include HIV/AIDS, tuberculosis, viral hepatitis, Hodgkin’s disease, autoimmune diseases, and radiation or chemotherapy treatments.

Platelets (Thrombocytes)

Platelets are very small, non-nucleated discs of diameter 2-4 µm, obtained from cytoplasm of megakaryocytes in red bone marrow. Normal platelet count lies between 200×10⁹/L and 350×10⁹/L (2,00,000-3,50,000/mm³).

Functions of Platelets:

• Vasoconstriction: They become sticky and adhere to the damaged wall of blood vessel secreting serotonin that constricts the vessel.
• Platelet Plug Formation: A positive feedback mechanism where adhered platelets attract passing platelets to form a temporary seal.
• Coagulation (Blood Clotting): Prothrombin activator converts prothrombin to thrombin, which converts fibrinogen to fibrin.
• Fibrinolysis: Breakdown of the clot and healing of damaged blood vessel.

Role in Health and Disease:

• Thrombocytosis: Higher-than-normal platelet count. Can lead to stroke or myocardial infarction.
• Thrombocytopenia: Lower-than-normal platelet count. Leads to difficulty in stopping bleeding.

ERYTHROCYTES – ABNORMAL CELLS AND THEIR SIGNIFICANCE

Normal mature erythrocytes are disc-shaped, biconcave cells which do not have nucleus. Any variations in size, shape, or colour of erythrocytes can be examined under microscope using Wright or similar Romanowsky-type stain.

Variations in Size

Normal erythrocyte has an average diameter of 7.2 µm (ranges between 6.8-7.5 µm).

• Microcytic: Size remains less than 6.2 µm. Occurs in iron deficiency anaemia, thalassemia.
• Normocytic: Normal size (6.2-8.2 µm).
• Macrocytic: Size exceeds 8.2 µm. Occurs in vitamin B₁₂ or folate deficiency.

Anisocytosis: Increased variation in cell size.

Variations in Shape (Poikilocytosis)

• Acanthocytes: Multiple thorny, spike-like projections. Seen in abetalipoproteinaemia, liver cirrhosis.
• Blister Cells: One or more vacuoles resembling blisters. Seen in severe burns, pulmonary emboli.
• Burr Cells (Echinocytes): Spiny projections. Seen in uraemia, pyruvate kinase deficiency.
• Elliptocytes: Rod, cigar, or sausage-like shape. Seen in hereditary elliptocytosis, thalassemia.
• Sickle Cells (Drepanocytes): Formed in sickle cell anaemia (HbS). Caused by mutation in β-globin gene.
• Spherocytes: Spherical shape. Seen in hereditary spherocytosis, autoimmune haemolytic anaemia.
• Target Cells (Codocytes): Excess membrane compared to cytoplasm. Seen in thalassemia, liver disease.
• Teardrop Cells (Dacrocytes): Pear-shaped cells. Seen in myelofibrosis, megaloblastic anaemia.

Dpharmguru’s exam insights:

Sickle cell anaemia is caused by a single nucleotide mutation (GAG to GTG) in the β-globin gene, resulting in HbS. This is a classic example of a point mutation causing disease. Remember: Sickle cells are also called drepanocytes!

Alterations in Colour

• Hypochromia: Reduced staining due to increased central pallor. Indicates iron deficiency anaemia.
• Hyperchromia: More intensely stained cells. Seen in spherocytes.
• Anisochromasia: Increased variability in degree of staining.
• Dimorphism: Presence of two types of RBCs (hypochromic and normochromic).
• Polychromasia: RBCs showing pinkish-blue colour. Indicates immature RBCs released from bone marrow.

Inclusions in Erythrocytes

• Howell-Jolly Bodies: Round, dark-blue to purple inclusions. Seen in haemolytic anaemia, postsplenectomy.
• Pappenheimer Bodies (Siderotic Granules): Purple dots representing iron particles. Seen in iron-loading anaemia, hyposplenism.
• Heinz Bodies: Precipitated and denatured haemoglobin. Seen in G6PD deficiency, drug-induced haemolytic anaemia.
• Basophilic Stippling: Tiny, dark-blue granules (accumulated RNA). Seen in lead poisoning.
• Cabot Rings: Loop-shaped or figure 8-shaped structures. Remnants of microtubules. Seen in pernicious anaemia, lead poisoning.

PART 2: PATHOLOGY OF URINE

Urine is an excretory product of the body formed in the kidney. Normal urine contains waste products, such as, urea, uric acid, creatinine, etc. and certain salts, such as, chlorides, sulphates, etc. Urine examination helps in the diagnosis of various renal as well as systemic diseases or disorders.

Normal Constituents of Urine

Inorganic Constituents:

• • Chloride: 8-15 g/day. Increased: polydipsia; Decreased: excessive sweating, vomiting.

• • Sulphate: 1 g/day. Increased: homocysteinuria; Decreased: renal impairment.

• • Calcium: 200 mg/day. Increased: hyperparathyroidism; Decreased: tetany.

• • Ammonia: 0.5-0.8 g/day. Increased: diabetic ketoacidosis; Decreased: alkalosis, nephritis.

• • Urea: 0.5-0.8 g/day. Increased: diabetes mellitus; Decreased: liver disease, kidney failure.

• • Uric Acid: 0.6-1 g/day. Increased: leukemia; Decreased: gout.

• • Creatinine: 2 g/day (male), 1 g/day (female). Increased: muscle disorders; Decreased: renal failure.

Physical Characteristics of Urine:

• • Colour: Yellow-amber (normal). Red indicates RBCs (kidney damage).

• • Odour: Sweet or fruity smell indicates ketones (diabetes).

• • pH: 4.6-8 (average 6.0). High protein diet makes urine acidic; vegetarian diet makes it alkaline.

• • Density (Specific Gravity): 0.001-0.035.

• • Turbidity: Fresh urine is clear or slightly cloudy. Increased turbidity indicates UTI or obstruction.

Abnormal Constituents of Urine and their Significance

• • Proteins (Proteinuria): Presence of albumin and globulin. Seen in glomerulonephritis, nephrotic syndrome.

• • Glucose (Glycosuria): Seen in diabetes mellitus, endocrinal disorders.

• • Ketone Bodies: Seen in starvation, diabetes mellitus, pregnancy.

• • Bilirubin and Bile Salts: Seen in obstructive or hepatic jaundice, biliary obstruction.

• • Blood (Haematuria): Seen in kidney lesions, UTI, nephritis.

• • Urobilinogen: Seen in haemolytic jaundice, pernicious anaemia, liver diseases.

• • Porphyrins: Increased in liver diseases, porphyria.

Dpharmguru’s exam insights:

Remember the key abnormal urine constituents: (1) Proteinuria = kidney damage, (2) Glycosuria = diabetes, (3) Haematuria = bleeding in urinary tract, (4) Bilirubin = liver disease. These are almost guaranteed to appear in exams!

SUMMARY

Pathology of blood and urine is essential for diagnosing various diseases and disorders. Blood components include RBCs, WBCs, and platelets, each with specific functions and abnormalities. Urine analysis helps detect renal and systemic diseases through physical and chemical examination. Understanding the normal and abnormal findings in blood and urine is crucial for pharmacy students and healthcare professionals.

Dpharmguru’s exam insights:

In exams, pay special attention to: (1) The normal values of blood components, (2) The types and causes of RBC abnormalities, (3) The significance of abnormal urine constituents, and (4) The difference between B cells and T cells. Remember: “Blood and urine tell the story of the body—learn to read them!”

REFERENCES AND FURTHER READING

• Kumar, V., Abbas, A. K., & Aster, J. C. (2021). Robbins & Cotran Pathologic Basis of Disease (10th ed.). Elsevier.

• Hoffman, R., Benz, E. J., Silberstein, L. E., et al. (2018). Hematology: Basic Principles and Practice (7th ed.). Elsevier.

• Park, K. (2022). Park’s Textbook of Preventive and Social Medicine (26th ed.). Banarsidas Bhanot Publishers.

• National Institutes of Health (NIH). (2022). Blood and Urine Pathology Resources. Retrieved from https://www.nih.gov.

• World Health Organization (WHO). (2022). Laboratory Diagnosis Resources. Retrieved from https://www.who.int.

 

Disclaimer: This article is for educational purposes only and does not constitute medical advice. Always consult qualified healthcare professionals for medical concerns.