ROUTINE TESTS – Page 2

HANDLING AND STORAGE OF BIOLOGICAL SPECIMEN

BLOOD

Handling

All blood specimen

Prevent haemolysis
Collect specimen in a tube at room temperature

Serum

Separate serum from blood within 30-45 min after collection

Plasma

Mix anticoagulant gently but thoroughly with blood specimen immediately after collection

Storage

For blood specimen:

Refrigerate at 4°C to retard alterations in physical and chemical composition of specimen

Plasma and serum

These can be frozen but whole blood should not be frozen as it may cause Haemolysis

URINE

Handling

Avoid contamination of inside of specimen contamination

Storage

If urine cannot be tested within one hour after collection, refrigerate it or add an appropriate preservative

MICROBIOLOGICAL SPECIMEN

Handling

Avoid contamination of swab used to collect specimen
Avoid contamination of inside of the specimen container.
Protect yourself from contamination from biological specimen
Protect anaerobic specimen from exposure to air.

Storage

Transport the specimen as soon as possible.
If not possible, place the specimen in a transport medium or inoculate in suitable culture media.
For most specimen: Place in refrigerator at 4°C to prevent drying, death or overgrowth of specimen with extraneous microorganisms.

STOOL

Handling

Collect the specimen in a clean container.
For detection of ova and parasites, keep the specimen warm

Storage

For most accurate results, deliver specimen to the laboratory immediately
For a delayed transportation, mix with appropriate preservative or place in a transport medium.

BLOOD GLUCOSE TEST

Mainly tested for diagnosis and management of diabetes mellitus

What are the Normal ranges for blood glucose?

Adults
– Fasting (plasma) 3.6–6.4 mmol/l
– Random (plasma) 3.3–7.4 mmol/l
Children
– Fasting (plasma) 2.4–5.3 mmol/l
Newborn values are slightly lower, i.e. 1.1–4.4

Causes of raised blood glucose levels

Hyperglycaemia (Raised blood glucose levels) may accompany pancreatic disease
and some endocrine disorders such as thyrotoxicosis and Cushings syndrome. Steroid therapy may also cause hyperglycaemia. Transient hyperglycaemia
often occurs following severe stress, e.g. after surgery, injury, shock, infections, or severe burns.

Causes of low blood glucose levels

A low blood glucose level is called hypoglycaemia.
Persistent occurrences of hypoglycaemia with glucose levels less than 2.2 mmol/l accompanied by symptoms such as fainting, fits, sweating, hunger, pallor, confusion, or violence, should be investigated.
Causes of hypoglycaemia include severe malnutrition, kwashiorkor, severe liver disease, alcoholic excess, insulin secreting tumours, Addison’s disease,
and certain drugs. Commonly, however, markedly reduced blood glucose levels occur following the overtreatment of diabetes.

Neonatal hypoglycaemia: Newborn infants may suffer hypoglycaemia when blood glucose levels fall below 1.1 mmol/l. Infants particularly at risk are
underweight poorly nourished babies, twins, premature infants, and babies born of diabetic mothers. It is important to detect hypoglycaemia of the newborn because without treatment brain damage may
occur.
Malaria associated hypoglycaemia: In severe malaria, hypoglycaemia is a common finding and can increase mortality particularly in young children.
Hypoglycaemia can also occur in those being treated with quinine and quinidine.

HAIR SAMPLE FOR FUNGAL DETECTION

• A Wood’s light, if available, may be helpful in selecting specimens.

• Pluck broken or lustreless hairs from periphery of lesion. Scrape scalp from edge of hair loss area.

• Do not cut hair.

• If hair are broken off (endothrix), it often may be necessary to scrape the coiled hair stubble from the scalp with a sterile blade or slide edge, rather than plucking with tweezers.

• Submit specimen to laboratory in sterile petri dish.

See also:

OCCULT BLOOD TEST

Bleeding into the gastrointestinal tract may be rapid with the vomiting of blood (haematemesis) or the passage of blood through the rectum (melaena).
When the bleeding is chronic with only small amounts of blood being passed in the faeces, the blood (or its breakdown products) is not recognized in the faeces and is referred to as occult (hidden)
blood.

When is Occult blood requested

Requests for occult blood testing are usually made to investigate the cause of iron deficiency anaemia or to assist in the diagnosis of bleeding lesions of the gastrointestinal tract, e.g. peptic ulcer,
carcinoma, or diverticulosis.

Methods applied in Occult blood Test

Chemically using guaiac based reagents prepared in the laboratory, e.g. aminophenazone test, or ready-made reagent in kit tests, e.g. Hema-Screen.
Immunologically using a haemoglobin specific cassette or strip test such as the Instant-View
Immunological tests are more expensive

Evaluation of Occult blood test

Specificity of occult blood tests:

Chemical tests are not specific for haemoglobin. They are based on the principle that haemoglobin and its derivatives react in a similar way to peroxidase
enzymes, i.e. they catalyze the transfer of an oxygen atom from a peroxide such as hydrogen peroxide to a chromogen
such as guaiacum, 2,6-dichlorophenolindophenol or aminophenazone. Oxidation of the chromogen is shown by the production of a blue, blue-green, or pink colour.

In chemical tests, non-haemoglobin substances with peroxidase activity can therefore cause false positive reactions.
Other substances can interfere with peroxidase activity resulting in false negative results. The specificity of chemical tests can be improved by dietary restriction.
Immunological occult blood tests are specific for the detection of human haemoglobin in faeces. A monoclonal antibody directed against human haemoglobin is used. This
selectively binds to human haemoglobin present in the faeces.

Sensitivity of occult blood tests:

Considerable variation of
sensitivity is shown by both chemical and immunological occult blood tests. Highly sensitive tests can be misleading because they detect trace amounts of blood which can be found in normal faeces. Highly sensitive chemical tests can give false positive reactions when faeces contain dietary substances which have peroxidase-like activity. Tests of low sensitivity can also be misleading because they may fail to detect small
amounts of blood which are pathological.

SKIN SCRAPING FOR FUNGAL DETECTION

• Clean skin with 70% alcohol.

• Scrape edges of lesion (as edge has greatest amount of viable fungus) with a blunt scalpel blade.

• Collect skin scales in a sterile petri dish or similar wide-mouthed container or alternatively, skin scrapings may be collected in a clean, dry piece of paper folded securely with Scotch tape and labelled properly.

• If a skin scraping does not yield sufficient material, then a swab or Scotch tape could be pressed on the lesion

NAIL SAMPLE FOR FUNGAL DETECTION

• Clean nail with 70% alcohol.

• Examine for damaged, discoloured, brittle or dystrophic area.

• Material should be taken from the affected areas.

• Entire thickness of the damaged nail should be cut as far back as possible. Any crumbly material or material under the nail should be collected and sent in a sterile container.

• If skin lesions are present they should be scraped and the material collected should be sent separately.

See also: