Microbiology
Principles
Giemsa-stained blood film microscopy is typically used for the diagnosis of which of the following:
Answer:
Giemsa-stained blood film microscopy can be used to identify malarial parasites.Principles of Investigation
Microbiology / Principles / Principles of Investigation
Last Updated: 21st April 2019
Specimen Types
Examples of specimens required to diagnose infection:
| Infection | Specimen |
|---|---|
| UTI | Midstream Specimen of Urine (MSSU) |
| Skin wound | Wound swab |
| Meningitis | CSF and blood |
| Nonspecific pyrexia | Blood culture and serology |
| Pneumonia | Blood and sputum |
Specimen Culture
Specimen culture allows amplification of organism quantity to allow reliable detection. There are liquid medium and solid medium types of culture.
Specimen Examination
Specimens may be examined under microscopy:
- Stool may be examined directly under light microscopy to detect parasites in stool.
- Special stains can be used to help identify certain organisms under light microscopy. For example:
- Giemsa staining can be used to identify malaria
- Ziehl-Neelsen staining can be used to identify Mycobacterium tuberculosis
- Gram staining is used to differentiate between two large groups of bacteria based on their different cell wall constituents (staining purple/blue if Gram-positive and red if Gram-negative)
- Immunofluorescence microscopy may be used to identify respiratory syncytial virus (RSV).
| Infection | Investigation |
|---|---|
| Stool: parasites | Direct light microscopy |
| CSF: bacteria | Gram stain |
| Sputum: TB | Ziehl-Neelsen stain |
| Blood: malaria | Giemsa stain |
| Sputum: RSV | Fluorescence microscopy |
Serology
Infection can also be diagnosed by detecting the immune response to the pathogen (the serology); for example the trend of rising or falling antibodies, or by the presence of a specific antibody or antigen. These techniques are used for organisms that are difficult to grow, such as viruses e.g. HIV, Hepatitis B.
Molecular Techniques
Nucleic acid amplification techniques (NAATs) detect specific regions of the genome from the pathogen and are useful to detect organisms that are slow-growing or difficult to grow e.g. Mycobacterium tuberculosis or Chlamydia trachomatis.
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
