9. CLINICAL LABORATORY TESTS USED IN THE EVALUATION OF DISEASE STATES – SIGNIFICANCE AND INTERPRETATION OF TEST RESULTS

CLINICAL LABORATORY TESTS: A TEACHER’S COMPREHENSIVE GUIDE

Welcome, future clinical pharmacists and healthcare professionals!

Clinical laboratory tests are essential tools in modern medicine that involve collecting a sample of blood, tissue, or other biological matter from a patient by a skilled medical professional. The sample is then sent to the clinical laboratory where it is examined by specially trained medical professionals using suitable equipment. These tests provide critical information for diagnosis, treatment monitoring, and disease prevention.

As a pharmacy educator with years of experience teaching clinical pharmacy and laboratory medicine, I have observed that students often struggle to interpret laboratory test results and understand their clinical significance. The ability to interpret laboratory data is essential for rational drug therapy and patient care. A pharmacist who understands laboratory tests can better monitor drug therapy, detect adverse effects, and optimize treatment regimens.

In this comprehensive guide, I will walk you through the major clinical laboratory tests—from haematological tests and liver function tests to renal function tests, thyroid function tests, cardiac tests, pulmonary function tests, and fluid-electrolyte balance. By the end of this article, you will have a thorough understanding of the normal ranges, clinical significance, and interpretation of test results. Let us begin our journey into the world of clinical laboratory medicine.

Dpharmguru’s exam insights:

Clinical laboratory tests are frequently tested in pharmacy exams. Remember: Each test has a normal range, and deviations from this range indicate specific pathological conditions. Key concepts include: Complete Blood Count (CBC), Liver Function Tests (LFTs), Renal Function Tests (RFTs), Thyroid Function Tests (TFTs), Cardiac Markers, and Pulmonary Function Tests (PFTs). Pay special attention to the clinical significance of abnormal values—this is what makes the difference between a pharmacist and a great clinical pharmacist!

9.1. HAEMATOLOGICAL TESTS

Haematological tests evaluate the cellular components of blood—red blood cells, white blood cells, and platelets—as well as various proteins and substances in the blood. These tests are fundamental for diagnosing anaemia, infections, bleeding disorders, and many other conditions.

1. Haemoglobin Value

Haemoglobin is the red coloured pigment of blood consisting of globin (96%) and haem (the iron-containing pigment, 4%). Its concentration is expressed in gram percentage.

Normal Range:

• Male: 14 to 18 g/dl
• Female: 12 to 16 g/dl
• Infant: 9.5 to 13 g/dL

Significance: Values of haemoglobin below the normal range indicate anaemia and leukaemia; while values above the normal range indicate polycythaemia.

2. Red Blood Cell (RBC) Count

RBCs are abundantly present in the blood and are red coloured due to the presence of haemoglobin. RBCs are formed in the bone marrow.

Normal Range:

• Male: 4.5-5.5 million/mm³
• Female: 3.5-5.5 million/mm³
• Children: 4.0-5.5 million/mm³

Significance: RBC count above normal indicates heart ailment, polycythaemia, cholera, diarrhoea, polyuria, and severe burns. RBC count below normal indicates anaemia and leukaemia.

3. Hematocrit (Hct)

Hematocrit estimates the percentage by volume of RBCs in a whole blood sample. For example, 40% Hct indicates that a 100ml blood sample has 40ml of blood cells.

Normal Range:

• Male: 40-50%
• Female: 37-47%
• Infant: 32-42%

Significance: Shock, dehydration, haemorrhage, or excessive IV fluid administration can decrease Hct. Abnormal Hct often correlates with abnormal RBC count.

4. Reticulocyte Count (Retic Count)

This test evaluates the definite numbers of reticulocytes (immature RBCs) in blood.

Normal Range: Approx. 1% of normal RBC counts (50,000); results vary between 0.5-1.5%.

Significance: Elevation indicates the body is reacting to pathologies like haemorrhage, anaemia, haemolysis, or other disease processes. Lowered count indicates anaemia or associated disorders.

5. White Blood Cell (WBC) or Total Leucocyte Count (TLC)

WBCs (leucocytes) are colourless cells with nuclei, larger in size but fewer in number than RBCs.

Normal Range:

• Male: 6,000-8,000 million/mm³
• Female: 8,000-10,000 million/mm³
• Children: 10,000-20,000 million/mm³

Significance: TLC higher than normal (leucocytosis: 11000-20000 million/mm³) indicates appendicitis, leukaemia, pneumonia, diphtheria, small-pox, tonsillitis, meningitis, rheumatic fever, asthma, diabetic coma, and uraemia. TLC lower than normal (leucopenia: below 4000 million/mm³) indicates typhoid, hepatitis, influenza, measles, paratyphoid, aplastic anaemia, starvation, anxiety, agranulocytosis, and exposure to UV radiations.

6. Differential Leucocyte Count (DLC)

WBCs are of the following types:

• Neutrophils: 60-70%
• Eosinophils: 1-4%
• Basophils: 0-2%
• Monocytes: 5-10%
• Lymphocytes: 20-30%

Significance: High neutrophil count (neutrophilia) indicates severe bacterial infections. High eosinophil count (eosinophilia) indicates intestinal parasites, allergic conditions, asthma, and skin conditions. High lymphocyte count (lymphocytosis) indicates whooping cough, mumps, influenza, tuberculosis, and diabetes.

7. Erythrocyte Sedimentation Rate (ESR)

When anticoagulant blood is held in a vertical column, the rate at which erythrocytes sediment under their own weight is termed ESR.

Normal Range (Westergren Method):

• Male: <15 mm/hr
• Female: <20 mm/hr
• Child: <10 mm/hr

Significance: High ESR indicates rheumatic fever, rheumatoid arthritis, tuberculosis, syphilis, cancer, pneumonia, and malignant tumours. Low ESR indicates allergic conditions.

8. Platelets

Platelets are involved in blood clotting and remain in circulation for 8-12 days.

Normal Range: 150-400 x 10⁹/L

Significance: Reduced platelets (thrombocytopenia) occurs due to increased destruction or reduced formation. Increased platelets (thrombocytosis) occurs during malignancy, inflammatory diseases, and blood loss.

9. Coagulation or Blood Clotting Time

Normal Range (Lee and White Method): 5-15 minutes

Significance: Increased clotting time indicates haemophilia, vitamin K deficiency, obstructive jaundice, dicoumarol therapy, heparin therapy, pneumonia, and leukaemia. Decreased clotting time indicates thrombosis and embolism.

10. Blood Sugar

Normal Range: 80-120mg/100ml

Significance: Increased blood sugar (hyperglycaemia) leads to diabetes (blood sugar level rises to 500mg/100ml). Decreased blood sugar (hypoglycaemia) occurs due to insulin overdosage, pancreatic tumour, adrenal cortical insufficiency, and hypopituitarism.

Dpharmguru’s exam insights:

Haematological tests are the most frequently tested laboratory tests. Remember the “Rule of 3” for RBCs: 4.5-5.5 million (males), 3.5-5.5 million (females). Haemoglobin: 14-18 (males), 12-16 (females). WBC count: 6,000-8,000 (males), 8,000-10,000 (females). Platelets: 150,000-400,000. These values are the cornerstone of haematological interpretation!

9.2. LIVER FUNCTION TESTS

Increased levels of ALP, SGOT, and SGPT enzymes indicate liver dysfunction. These tests reflect liver damage but do not evaluate its functional ability.

1. Serum Bilirubin

Bilirubin is the breakdown product of haemoglobin and is the major pigment in bile.

Normal Range: Total serum bilirubin: 0.3-1.3 mg/dL; Direct bilirubin: 0.1-0.4 mg/dL

Significance: Increased bilirubin indicates jaundice. Increased total bilirubin indicates haemolysis. Increased total and direct bilirubin indicates biliary obstruction. Increased indirect bilirubin indicates intrahepatic cholestasis. Increased direct and indirect bilirubin indicates liver cell necrosis.

2. Serum (Plasma) Proteins

Albumin and globulins (α, β, and γ) are the prime plasma proteins.

Normal Range: Total serum proteins: 6-8gm/dL; Serum albumin: 3.5-5.1gm/dL; Serum globulin: 1.8-3.1gm/dL; Albumin/Globulin ratio: 0.8 to 2.0

Significance: Decreased total protein indicates oedema, haemorrhage shock, extensive burns, acute infectious diseases, uncontrolled diabetes mellitus, hyperthyroidism. Increased total protein indicates dehydration. Increased globulin indicates chronic conditions like rheumatoid arthritis, kala azar, and tuberculosis.

3. Alkaline Phosphatase (ALP)

ALP is produced in the liver, bones, small intestine, and kidneys. It facilitates the splitting of phosphate group from monophosphoric esters.

Normal Range: 29-92 IU/L

Significance: Low ALP indicates hypo-phosphatacia. High ALP indicates rickets, osteomalacia, obstructive jaundice, and impaired absorption of vitamin D and calcium.

4. SGOT (AST) – Aspartate Transaminase

SGOT is mainly found in the heart and liver, and to a lesser extent in skeletal muscles, kidneys, and pancreas.

Normal Range: 0-40 U/L

Significance: Increased SGOT indicates liver diseases (viral hepatitis, toxic hepatitis, cirrhosis), cardiac diseases (myocardial infarction, congestive heart failure), skeletal muscle damage, acute pancreatitis, and pulmonary embolism. Decreased SGOT indicates deficiency of Vitamin B6.

5. SGPT (ALT) – Alanine Transaminase

SGPT is mainly found in the liver cells, and to a lesser extent in heart, skeletal muscles, and kidneys.

Normal Range: 5-36 U/L

Significance: Increased SGPT indicates liver cell damage. In acute myocardial infarction, SGPT rises less consistently than SGOT. Decreased SGPT indicates Vitamin B6 deficiency.

6. Serum Cholesterol (Lipid Profile)

This test measures four types of fats in blood:

• Total Cholesterol: <200 mg/dl
• LDL (Bad Cholesterol): <100 mg/dl
• HDL (Good Cholesterol): ≥100 mg/dl
• Triglycerides: <150 mg/dl

Significance: Increased cholesterol indicates higher risk of atherosclerosis, heart disease, and stroke. Decreased cholesterol indicates underlying disease like cancer or haemorrhagic stroke.

Dpharmguru’s exam insights:

Liver function tests are frequently tested. Remember: SGOT/AST is more specific for heart, SGPT/ALT is more specific for liver. The ALT/AST ratio can help differentiate between alcoholic liver disease (AST:ALT >2:1) and viral hepatitis (ALT>AST). ALP is elevated in biliary obstruction. Bilirubin elevation indicates jaundice—differentiate between pre-hepatic (indirect), hepatic (both), and post-hepatic (direct) causes!

9.3. RENAL FUNCTION TESTS

Renal or kidney function can be evaluated by urine tests. A routine urinalysis is performed when any kidney problem is suspected.

Urine Analysis

Physical Examination:

• Colour: Normal: Yellow-amber. Red indicates RBCs (kidney damage). Dark indicates dehydration.
• Odour: Sweet/fruity indicates diabetes (ketones).
• pH: Normal: 4.5-8.0 (usually 6.0).
• Density (Specific Gravity): Normal: 1.001-1.035. High indicates diabetes mellitus or nephrosis. Low indicates diabetes insipidus.
• Turbidity: Increased turbidity indicates UTI or obstructions.

Chemical Examination:

• Proteins (Proteinuria/Albuminuria): Indicates kidney disease.
• Glucose (Glycosuria): Indicates diabetes mellitus.
• Ketone Bodies: Indicates starvation, diabetes mellitus, pregnancy.
• Bilirubin (Bilirubinuria): Indicates obstructive or hepatic jaundice.
• Blood (Haematuria): Indicates kidney lesions, UTIs, nephritis.
• Urobilinogen: Indicates liver diseases (viral hepatitis, cirrhosis).

Additional Renal Function Tests

1. Blood Urea Nitrogen (BUN): Normal: 10-12 mg/dL. Increased indicates kidney dysfunction. Decreased indicates malnutrition, liver disease.

2. Creatinine Test: Normal: 1-2 mg/dL. Elevated creatinine in blood with low levels in urine indicates kidney disease.

3. Creatinine Clearance Test: Normal: 90-139 ml/min (males), 80-125 ml/min (females). Low values indicate kidney problems, kidney failure.

4. Urea Clearance Test: Normal: 12-20 gm/24 hours. Low levels indicate kidney problems.

5. Urine Osmolality Test: Normal: 500-850 mOsm/kg. Elevated indicates dehydration, high glucose. Low indicates kidney failure, renal tubular necrosis.

6. Urine Concentration Test: Normal: 1.000-1.030. Highly concentrated indicates dehydration, glycosuria. Low concentration indicates diabetes insipidus, kidney failure.

9.4. THYROID FUNCTION TESTS

Thyroid function tests are a group of blood tests performed to assess thyroid gland functioning.

• TSH (Thyroid Stimulating Hormone): Normal: 0.4-4.0 mU/L. Elevated indicates primary hypothyroidism. Low indicates hyperthyroidism.
• T3 (Triiodothyronine): Normal: 100-200 ng/dL. Elevated indicates hyperthyroidism. Low indicates hypothyroidism.
• Free T3 (FT3): Normal: 2.3-4.1 pg/mL. Increased indicates hyperthyroidism. Decreased indicates hypothyroidism.
• T4 (Thyroxine): Normal: 5.0-11.0 μg/dL. High TSH + low FT4 = primary hypothyroidism. Low TSH + low FT4 = secondary hypothyroidism.
• Free T4 (FT4): Normal: 0.9-1.7 ng/dL. Increased indicates overactive thyroid (Grave’s disease). Decreased indicates hypothyroidism.
• TBG (Thyroid Binding Globulin): Normal: 13-39 μg/dL. Increased indicates hypothyroidism, liver disease, pregnancy. Decreased indicates hyperthyroidism, malnutrition.
• Calcitonin: Used to identify medullary thyroid cancer.
• Thyroglobulin: Used to identify thyroiditis and track thyroid cancer treatment.

Dpharmguru’s exam insights:

Thyroid function tests are frequently tested. Remember the “TSH first” approach: TSH is the most sensitive test for thyroid dysfunction. Primary hypothyroidism = high TSH + low FT4. Primary hyperthyroidism = low TSH + high FT4. Secondary hypothyroidism = low TSH + low FT4. T3 is the active hormone, T4 is the precursor.

9.5. TESTS ASSOCIATED WITH CARDIAC DISORDERS

• Pulse Rate: Normal adult: 70-80/minute. Increased (tachycardia) indicates emotional excitement, fever, exercise. Decreased (bradycardia) indicates certain cardiac conditions.
• Blood Cholesterol: Increased indicates diabetes mellitus, obstructive jaundice, obesity, myxoedema. Decreased indicates hyperthyroidism and pernicious anaemia.
• Creatine Phosphokinase (CPK/CK): Normal: 10-120 mcg/L. Elevated indicates heart attack, brain injury, muscular dystrophies, trauma.
• Lactic Acid Dehydrogenase (LDH/LD): Normal: 135-225 U/L (males), 135-214 U/L (females). Five isoenzymes: LDH1 (heart), LDH2 (heart), LDH3 (lungs), LDH4 (liver), LDH5 (liver/skeletal muscles).
• Troponins (Tn): Normal: 0.7-1.5 ng/ml. Increase >2.0 μg/L indicates acute myocardial injury. Tnl is highly sensitive and specific for myocardial tissue.

9.6. PULMONARY FUNCTION TESTS

These tests assess how effectively the lungs are functioning.

• Spirometry: Measures how much air a person can inhale and exhale.
• Body Plethysmography: Measures how much air is present in the lungs.
• Lung Diffusion Capacity: Measures how efficiently oxygen is transported to the bloodstream.
• Tidal Volume (VT): Air inhaled during quiet breathing.
• Inspiratory Reserve Volume (IRV): Maximal volume inhaled from quiet breathing.
• Expiratory Reserve Volume (ERV): Maximal volume exhaled from quiet breathing.
• Residual Volume (RV): Air remaining after maximal exhalation.
• Total Lung Capacity (TLC): Sum of 4 primary volumes.
• Vital Capacity (VC): Volume exhaled from maximal inspiration to maximal expiration.
• Forced Vital Capacity (FVC): Amount of air forced and immediately exhaled.
• Forced Expiratory Volume (FEV): Air exhaled during 1st, 2nd, and 3rd seconds of FVC.
• Peak Expiratory Flow Rate (PEFR): Rate at which lungs expel air.

9.7. FLUID AND ELECTROLYTE BALANCE

About 56% of adult human body is fluid. Most of this fluid is intracellular (inside cells); about one-third is extracellular (outside cells).

Body Water Compartments (70kg person):

• Total Body Water: 42L (60%)
• Extracellular Water: 14L (33%) – Plasma: 3.5L (8%), Interstitial: 10.5L (25%)
• Intracellular Water: 28L (67%)

9.7.1. Disorders of Water and Electrolyte Balance

1. Dehydration or Fluid Volume Deficit (FVD): Body’s fluid levels drop when deficient in water and electrolytes.

Causes: Vomiting, diarrhoea, gastrointestinal suctioning, excessive sweating.

Signs: Dry mucous membranes, anxiety, reduced alertness, dry skin, fatigue, hypouresis.

Treatment: Oral rehydration (ORS), intravenous fluids for severe cases.

ORS Formula (WHO):

• Sodium chloride: 2.6g
• Trisodium citrate dihydrate: 2.9g
• Potassium chloride: 1.5g
• Anhydrous Glucose: 13.5g

2. Fluid Volume Excess (FVE): Body retains both water and salt.

Causes: Impaired regulatory mechanisms, corticosteroid administration, excessive sodium intake.

Signs: Weight gain, peripheral oedema, distended neck veins, crackles in lungs, polyuria.

Treatment: Limiting sodium and water intake, diuretics.

3. Water Intoxication: Dangerous condition where water consumption exceeds body’s ability to excrete it, leading to hyponatremia.

Symptoms: Nausea, fatigue, headache, muscle spasms, confusion, seizures, unconsciousness, coma.

Treatment: Reducing water intake, IV fluids, medicines, hormone therapy.

Dpharmguru’s exam insights:

Fluid and electrolyte balance is a critical topic. Remember: Isotonic dehydration = loss of water and electrolytes equally. Hypertonic dehydration = more water loss than salt (common in fevers). Hypotonic dehydration = more salt loss than water (common in vomiting/diarrhoea). ORS is the cornerstone of treating dehydration—know the WHO formula! Water intoxication is a rare but dangerous condition caused by excessive water intake diluting sodium levels.

COMPARISON: KEY LABORATORY TESTS AND THEIR SIGNIFICANCE

FREQUENTLY ASKED QUESTIONS (FAQs)

1. What is the difference between SGOT and SGPT?

SGOT (AST) is mainly found in the heart and liver, while SGPT (ALT) is mainly found in liver cells. ALT is more specific for liver damage, while AST is more specific for cardiac damage. The ALT/AST ratio helps differentiate between alcoholic liver disease (AST:ALT >2:1) and viral hepatitis (ALT>AST).

2. What is the normal range for blood sugar?

Normal blood sugar is 80-120 mg/100ml (fasting). Values above indicate hyperglycaemia (diabetes), and values below indicate hypoglycaemia (insulin overdose, pancreatic tumour).

3. What is the significance of elevated troponin levels?

Troponin I (TnI) is highly sensitive and specific for myocardial tissue. Increase to more than 2.0 μg/L indicates acute myocardial injury (heart attack). Troponins are the gold standard for diagnosing myocardial infarction.

4. What does a high TSH level indicate?

High TSH indicates insufficient thyroid hormone production by the thyroid gland (primary hypothyroidism). The pituitary gland produces more TSH to stimulate the thyroid when it detects low thyroid hormone levels.

5. What is the difference between BUN and creatinine?

BUN measures nitrogen from urea (protein metabolism), while creatinine measures a by-product of muscle energy metabolism. Creatinine is more specific for kidney function, while BUN can be affected by protein intake and hydration status. The BUN/Creatinine ratio helps differentiate between pre-renal and renal causes of kidney dysfunction.

6. What is the WHO formula for ORS?

The WHO recommended ORS formula contains: Sodium chloride (2.6g), Trisodium citrate dihydrate (2.9g), Potassium chloride (1.5g), and Anhydrous Glucose (13.5g) per litre of water. This is the most effective treatment for dehydration due to diarrhoea and vomiting.

SUMMARY

Clinical laboratory tests are essential tools for diagnosis, monitoring, and treatment optimisation in modern healthcare. From haematological tests that evaluate blood cells to liver and renal function tests that assess organ health, thyroid function tests that evaluate endocrine status, cardiac markers that diagnose heart attacks, and pulmonary function tests that measure lung capacity—each test provides critical information for patient care.

Understanding the normal ranges and clinical significance of these tests is essential for every clinical pharmacist. The ability to interpret laboratory data enables pharmacists to monitor drug therapy, detect adverse effects, optimise dosing regimens, and improve patient outcomes. Fluid and electrolyte balance is another critical area—disorders like dehydration, fluid overload, and water intoxication require prompt recognition and appropriate management.

As I always tell my students: “A pharmacist who understands laboratory tests is not just dispensing medications—they are actively monitoring therapy, preventing adverse effects, and optimising patient outcomes. Laboratory data is the language of clinical decision-making. Learn to speak it fluently!”

REFERENCES AND FURTHER READING

• Pharmacy Council of India (PCI). (2022). Clinical Pharmacy and Laboratory Medicine Guidelines. New Delhi: PCI.
• World Health Organization (WHO). (2022). Laboratory Tests in Clinical Practice. Retrieved from https://www.who.int.
• American Society of Health-System Pharmacists (ASHP). (2022). Clinical Laboratory Interpretation. Retrieved from https://www.ashp.org.
• Fishbach, F. (2022). A Manual of Laboratory and Diagnostic Tests (11th ed.). Wolters Kluwer.
• Pagana, K. D., & Pagana, T. J. (2021). Mosby’s Manual of Diagnostic and Laboratory Tests (7th ed.). Elsevier.
• National Kidney Foundation. (2022). Renal Function Tests: Guidelines and Interpretation. Retrieved from https://www.kidney.org.

Disclaimer: This article is for educational purposes only and does not constitute medical advice. Always consult qualified healthcare professionals for medical concerns. Laboratory reference ranges may vary between laboratories—always refer to the specific reference ranges provided by your local laboratory.

written by:
Dr. N. Sujith Kumar

Dr. N. Sujith Kumar is a pharmacy educator, Pharm.D graduate, and academic content creator from Jawaharlal Nehru Technological University Kakinada (JNTUK), where he completed his Doctor of Pharmacy (Pharm.D) degree between 2015 and 2021. He has more than 7 years of experience creating pharmacy educational content, writing study materials, and reviewing academic articles for pharmacy students. He has also contributed guest articles to pharmacy education platforms, including PharmD Guru. At D.PharmGuru, his work focuses on simplifying complex Diploma in Pharmacy (D.Pharmacy) subjects into easy-to-understand notes, practical explanations, and exam-oriented educational resources for students across India. His areas of focus include Human Anatomy and Physiology, Pharmaceutics, Pharmacology, Pharmaceutical Chemistry, Hospital and Clinical Pharmacy, and other core D.Pharmacy subjects.

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