Investigations form a cornerstone of modern clinical practice. From simple bedside tests such as measuring temperature and blood pressure to complex laboratory studies and imaging techniques, they provide clinicians with vital information that supports diagnosis, guides treatment, and helps monitor disease progression. However, investigations are not an end in themselves. Their value lies in their correct interpretation and integration into the broader clinical picture, which must always begin with a careful history and physical examination.
Basic Clinical Observations
The simplest yet most fundamental investigations are the routine measurements of temperature, pulse, blood pressure, and respiratory rate. Collectively, these are often referred to as the “vital signs” because they provide an immediate snapshot of a patient’s physiological state.
Temperature
The normal body temperature ranges from 35.5–37.5°C (95.9–99.5°F). It is not a fixed value but fluctuates throughout the day, usually lowest in the early morning and highest in the evening.
- Fever (Pyrexia): An elevated temperature often indicates infection, but it can also result from non-infectious inflammatory processes, malignancies, or autoimmune conditions.
- Hyperthermia: A more dangerous rise in temperature due to failure of thermoregulation, as seen in heatstroke or adverse drug reactions (e.g., neuroleptic malignant syndrome).
- Hypothermia: Defined as a core temperature below 35°C. Causes include prolonged cold exposure, hypothyroidism, sepsis, or drug intoxication.
The clinician must not only record the temperature but also interpret its pattern. For example, intermittent fevers may suggest malaria, while sustained fever is more consistent with typhoid.
Pulse
The adult resting pulse typically ranges between 60 and 80 beats per minute, though infants and children naturally have faster rates, sometimes reaching up to 140 beats per minute.
- Tachycardia (↑ pulse): May occur in fever, anemia, dehydration, anxiety, hyperthyroidism, or cardiac arrhythmias.
- Bradycardia (↓ pulse): Common in athletes but may also be due to heart block, hypothyroidism, or drug effects (e.g., beta-blockers).
- Irregular pulse: Could indicate atrial fibrillation, ectopic beats, or other arrhythmias.
In addition to rate and rhythm, the character of the pulse (e.g., bounding, thready, collapsing) provides diagnostic clues.
Blood Pressure
Normal adult blood pressure lies around 120/80 mmHg, though values up to 140/90 mmHg may be acceptable in older adults.
- Hypertension: Persistent elevation is a major risk factor for cardiovascular disease, stroke, and renal failure. It often remains asymptomatic, hence the label “silent killer.”
- Hypotension: May indicate shock, blood loss, dehydration, or adrenal insufficiency. Sudden drops in blood pressure can compromise organ perfusion and are medical emergencies.
Repeated, accurate measurements in the correct clinical context are vital for reliable interpretation.
Respiratory Rate
Normal resting respiratory rate is 12–18 breaths per minute in adults.
- Tachypnea (↑ rate): Seen in chest infections, pulmonary edema, shock, anxiety, or metabolic acidosis.
- Bradypnea (↓ rate): May occur in drug overdose (opioids), raised intracranial pressure, or severe hypothermia.
- Abnormal breathing patterns: Such as Cheyne–Stokes respiration or Kussmaul breathing provide diagnostic insights into neurological or metabolic disorders.
Recording and interpreting respiratory rate is often neglected, but it remains one of the most sensitive indicators of acute illness.
Urinalysis
Urinalysis is a simple, inexpensive, and informative investigation performed on virtually all patients admitted to hospital. It provides immediate information about renal function, metabolic disorders, and systemic disease.
- Glucose: Its presence suggests diabetes mellitus, though stress hyperglycemia and pregnancy can also cause glycosuria.
- Ketones: Detected in diabetic ketoacidosis, starvation, or prolonged vomiting.
- Protein: Persistent proteinuria usually indicates renal disease, particularly glomerular or tubular pathology.
- Blood: Suggests urinary tract infection, stones, trauma, or tumor. Microscopic hematuria may be an early sign of malignancy.
- Bilirubin: Points towards hepatocellular disease or obstructive jaundice.
- Urobilinogen: Increased in hemolysis or hepatocellular disease, absent in obstructive jaundice.
Thus, urinalysis not only aids in diagnosis but also serves as a non-invasive tool for monitoring disease progression.
Blood Investigations
Full Blood Count (FBC)
The FBC provides critical information about the cellular components of blood.
Haemoglobin (Hb): Normal range is 13–18 g/dL (men) and 11.5–16.5 g/dL (women). Low Hb indicates anemia; elevated Hb occurs in polycythemia or chronic hypoxia (e.g., in COPD).
Haematocrit (Hct): The proportion of blood volume occupied by red cells (M 40–54%, F 37–47%). Raised in dehydration or polycythemia; reduced in anemia.
Mean Cell Volume (MCV): Reflects average red cell size (76–96 fL).
Microcytic (↓ MCV): Iron deficiency, thalassemia.
Macrocytic (↑ MCV): Vitamin B₁₂ or folate deficiency, alcoholism.
White Cell Count (WCC): Normal range 4–11 × 10⁹/L.
Elevated in infections, inflammation, or leukemia.
Low counts suggest bone marrow suppression, viral infections, or cytotoxic drug effects.
Platelets: Normal 150–400 × 10⁹/L.
Thrombocytopenia increases bleeding risk.
Thrombocytosis may accompany infection, inflammation, or myeloproliferative disorders.
Biochemistry
Biochemical analysis of blood provides insight into renal function, electrolyte balance, and metabolic status.
Sodium (135–145 mmol/L):
Hyponatremia may result from diuretic use, heart failure, or SIADH.
Hypernatremia often indicates dehydration or diabetes insipidus.
Potassium (3.5–5 mmol/L):
Hypokalemia causes muscle weakness, arrhythmias, often due to vomiting, diarrhea, or diuretics.
Hyperkalemia is life-threatening, seen in renal failure, acidosis, or potassium-sparing drugs.
Creatinine (70–150 μmol/L): A reliable marker of renal function. Elevated in renal failure, dehydration, or obstruction.
Urea: Also used to assess renal function but influenced by diet and hydration status.
Special biochemical tests:
Liver function tests (LFTs): Assess hepatocellular injury and cholestasis.
Thyroid function tests: Diagnose hypo- or hyperthyroidism.
Cardiac enzymes (e.g., troponins): Essential in diagnosing myocardial infarction.
Vitamin B₁₂ and folic acid levels: Important in evaluating macrocytic anemia.
Blood Glucose
Normal fasting glucose is 4–6 mmol/L.
- Hyperglycemia: Suggests diabetes mellitus, stress, or corticosteroid use.
- Hypoglycemia: May result from excess insulin, sepsis, liver failure, or adrenal insufficiency.
Competently performed bedside glucose tests can rapidly identify life-threatening hypo- or hyperglycemic episodes.
Microbiological Investigations
Virology
Viral serology is expensive and rarely needed in routine cases. It may, however, be indicated in diagnosing specific infections such as HIV, hepatitis, or Epstein-Barr virus.
Immunology
Tests in immunology are more frequently required than virology, especially for autoimmune diseases, immunodeficiencies, and complex systemic disorders. Examples include ANA (antinuclear antibody) for lupus and rheumatoid factor for rheumatoid arthritis.
Bacteriology
- Sputum and pus swabs: Critical in identifying causative organisms in respiratory and wound infections.
- Nasal and axillary swabs: Used to detect carriers of methicillin-resistant Staphylococcus aureus (MRSA) prior to surgical procedures.
- Stool samples: Traditionally used to detect Clostridium difficile infection, especially in hospitalized patients receiving antibiotics.
- Blood cultures: Gold standard for diagnosing septicemia. Samples should be collected before antibiotics are administered. Paired bottles (aerobic and anaerobic) from different sites increase diagnostic yield. Results are usually available within 24–48 hours.
Histopathology and Cytology
Biopsy
A biopsy remains the definitive diagnostic tool for many diseases, particularly cancers. By examining tissue microscopically, pathologists can identify the presence of malignancy, inflammation, or other abnormalities.
Cytology
Cytology involves examining individual cells rather than whole tissues. It is commonly used in cervical smears to detect precancerous changes, but its role in other areas, including dentistry, is limited. Cytology can suggest malignancy but often requires confirmation by biopsy.
Clinical Integration
Investigations are indispensable, but they must never replace clinical judgment. Test results should always be interpreted in light of the patient’s symptoms, history, and examination findings. Over-reliance on investigations risks misdiagnosis, unnecessary interventions, and increased healthcare costs.
For example:
- A raised WCC may point toward infection but could also indicate stress or leukemia.
- Protein in urine could reflect infection, but transient proteinuria is sometimes benign.
- A high potassium result in a hemolyzed sample may be spurious and lead to inappropriate treatment if not carefully considered.
Thus, clinicians must use investigations as tools that complement clinical reasoning, not as substitutes for it.
Conclusion
General clinical investigations—ranging from bedside vital signs to sophisticated laboratory analyses—form the backbone of modern medical practice. They provide essential diagnostic and prognostic information, guide therapeutic decisions, and help monitor patient progress.
However, their true value lies not in the numbers they generate but in the interpretation and integration of those results into a holistic understanding of the patient’s condition. A thoughtful clinician recognizes both the power and the limitations of investigations, using them judiciously to enhance rather than replace clinical acumen.
By mastering the principles outlined in this article, healthcare professionals can ensure that investigations remain effective tools in delivering safe, accurate, and patient-centered care.
References
- Kumar, P. & Clark, M. (2020). Kumar and Clark’s Clinical Medicine (10th ed.). Elsevier.
→ Comprehensive source for principles of investigations and interpretation of clinical findings. - National Institute for Health and Care Excellence (NICE). (2017). Investigations and patient assessment guidance (NG81).
- Talley, N. J. & O’Connor, S. (2018). Clinical Examination: A Systematic Guide to Physical Diagnosis (8th ed.). Elsevier.
→ Excellent resource for understanding bedside investigations and physical findings. - British Medical Association (BMA). (2023). Interpretation of Laboratory Results in General Practice.
→ Guidance on the interpretation of blood and urine tests in clinical contexts. - World Health Organization (WHO). (2022). Manual of Basic Laboratory Procedures in Clinical Bacteriology (2nd ed.). Geneva: WHO Press.
- Harrison, T. R., Kasper, D. L., Fauci, A. S., et al. (2022). Harrison’s Principles of Internal Medicine (21st ed.). McGraw-Hill Education.
→ Authoritative reference for biochemistry, hematology, and microbiology investigations. - Bain, B. J. (2019). Blood Cells: A Practical Guide (5th ed.). Wiley-Blackwell.
→ Essential for details on full blood count interpretation and hematological parameters. - BMJ Best Practice. (2024). Approach to investigations in clinical medicine.
- NICE Clinical Knowledge Summaries (CKS). (2024). Investigations and interpretation in primary care.
- Murray, P. R., Rosenthal, K. S., & Pfaller, M. A. (2021). Medical Microbiology (9th ed.). Elsevier.
→ Reference for virology, immunology, and bacteriology sections.