Unit 2: Diagnostic Methods used for Sputum, Urine and Stool Analysis
Table of Contents
1. Sputum Analysis
Sputum is mucus secreted from the lower respiratory tract (lungs and bronchi). It is not saliva. A sputum analysis is crucial for diagnosing respiratory diseases, especially infections.
Sample Collection: The best sample is a deep cough specimen collected first thing in the morning, as it is more concentrated. The patient should rinse their mouth with water first to avoid contamination with food or saliva.
Physical Characteristics (Macroscopic)
| Characteristic | Normal | Abnormal Constituents & Indication |
|---|---|---|
| Volume | Very small amount | Large volume (>100ml/day): Suggests lung abscess, bronchiectasis, or advanced tuberculosis. |
| Colour | Clear, white/opaque | Yellow-Green (Purulent): Presence of pus (neutrophils); indicates infection (pneumonia, bronchitis). Rusty Red: Presence of old blood; common in pneumococcal pneumonia. Bright Red (Haemoptysis): Fresh blood; indicates tuberculosis, lung cancer, or lung abscess. Pink & Frothy: Pulmonary oedema (heart failure). |
| Consistency | Mucoid (viscous) | Thick & Tenacious: Asthma, cystic fibrosis. Watery/Frothy: Pulmonary oedema. |
| Odour | Odourless | Foul/Putrid: Anaerobic bacterial infection (e.g., lung abscess). |
Microscopic Analysis (Abnormal Constituents)
- Pus Cells (Neutrophils): High numbers indicate an active bacterial infection.
- Eosinophils: High numbers are characteristic of bronchial asthma or allergic reactions.
- Bacteria: Identified by Gram stain (e.g., Gram-positive cocci in pneumonia).
- Acid-Fast Bacilli (AFB): A specific stain (Ziehl-Neelsen) is used to identify *Mycobacterium tuberculosis* (the cause of TB).
- Fungi: May indicate fungal infections (e.g., *Aspergillus*).
2. Urine Analysis (Urinalysis)
Urinalysis is a fundamental test that provides insights into kidney function and systemic diseases (like diabetes).
Physical Characteristics (Macroscopic)
| Characteristic | Normal | Abnormal Constituents & Indication |
|---|---|---|
| Colour | Pale yellow to deep amber (due to urochrome pigment) | Dark Red/Brown: Presence of blood (haematuria) or haemoglobin. Dark Yellow/Brown-Green: Presence of bilirubin (liver disease). Cloudy/Turbid: Presence of pus, bacteria, or crystals (infection, kidney stones). |
| pH | Slightly acidic (avg. 6.0, range 5.5-6.5) | High pH (Alkaline): Urinary tract infection (UTI) (bacteria convert urea to ammonia), or vegetarian diet. Low pH (Acidic): High protein diet, acidosis. |
| Specific Gravity (SG) | 1.012 – 1.024 | Measures the kidney's concentrating ability. High SG: Dehydration, diabetes mellitus (due to glucose). Low SG: Overhydration, chronic kidney disease (kidneys can't concentrate urine). |
Chemical Analysis (Abnormal Constituents)
These are typically tested using a "dipstick".
- Glucose (Sugar): Normally absent. Its presence (Glycosuria) is a strong indicator of Diabetes Mellitus.
- Protein: Normally absent (or in trace amounts). Its presence (Proteinuria) is a key sign of kidney disease (nephritis, nephrotic syndrome).
- Ketones: Normally absent. Their presence (Ketonuria) indicates the body is burning fat for energy. Seen in uncontrolled diabetes (diabetic ketoacidosis) and starvation.
- Bilirubin: Normally absent. Its presence indicates liver disease or bile duct obstruction (jaundice).
- Blood (Haemoglobin): Normally absent. Its presence (Haematuria) indicates bleeding in the urinary tract (kidney stones, infection, tumours).
- Nitrite: Normally absent. Its presence is a strong sign of a bacterial urinary tract infection (UTI) (bacteria convert nitrates to nitrites).
3. Stool Analysis
Stool analysis is essential for diagnosing gastrointestinal (GI) disorders, including infections, poor nutrient absorption, and cancer.
Physical Characteristics (Macroscopic)
| Characteristic | Normal | Abnormal Constituents & Indication |
|---|---|---|
| Colour | Brown (due to bilirubin/bile) | Black, Tarry: Digested blood from upper GI bleeding (e.g., stomach ulcer). Bright Red: Fresh blood from lower GI bleeding (e.g., haemorrhoids). Clay-Coloured/Pale: Lack of bile; indicates biliary obstruction (gallstones, liver disease). |
| Consistency | Soft and formed (Bristol Stool Scale Type 3-4) | Watery: Diarrhoea (e.g., infection, inflammation). Hard, pellet-like: Constipation. |
| Mucus | Small amount is normal | Copious mucus or bloody mucus: Abnormal. Indicates inflammation (e.g., dysentery, inflammatory bowel disease). |
Microscopic Analysis (Abnormal Constituents)
- Ova & Parasites (O&P): The presence of parasite eggs (ova) or active forms (cysts, trophozoites) confirms parasitic infections (e.g., *Amoeba*, *Giardia*, hookworm).
- Leukocytes (WBCs): Presence indicates inflammation of the intestine, often due to bacterial infections (e.g., *Shigella*, *Salmonella*).
- Fat (Steatorrhoea): Excessive fat in the stool indicates malabsorption, often due to pancreatic enzyme deficiency or Celiac disease.
- Occult Blood (Hidden Blood): A chemical test (FOBT) detects hidden blood, which can be an early sign of colorectal cancer.
Practical Component: Detection in Urine
This is performed using a Urine Dipstick, which is a plastic strip with small square-colored fields.
Procedure:
- Collect a midstream urine sample in a clean container.
- Dip the test strip into the urine, ensuring all colored fields are submerged, for a few seconds.
- Remove the strip and tap it on the side of the container to remove excess urine.
- Wait for the specified time (e.g., 30-60 seconds) for the results to appear.
- Compare the colors of the fields on the strip to the color chart on the bottle.
Detection:
- pH: The pH field will change color, corresponding to a pH value (e.g., 5, 6, 7). Normal is ~5-7.
- Sugar (Glucose): If glucose is present, the field will change color (e.g., from yellow to green/brown). Normally, this should be negative.
- Protein: If protein is present, the field will change color (e.g., from yellow to blue/green). Normally, this should be negative.