Page 8 - Clinical Biochemistry 08PB804

Midstream Clean Catch Specimen

This is the preferred type of specimen for culture and sensitivity testing because of the
reduced incidence of cellular and microbial contamination.

Patients are required to first cleanse the urethral area then void the first portion of the urine
stream into the toilet then collected into a clean container.

Timed Collection Specimen

Among the most commonly performed tests requiring timed specimens are those measuring
creatinine, urine urea nitrogen, glucose or analytes such as catecholamines that are
affected by diurnal variations.

A timed specimen is collected to measure the concentration of these substances in urine over a
specified length of time, usually 8 or 24 hours.

In this collection method, the bladder is emptied prior to beginning the timed collection. Then,
for the duration of the designated time period, all urine is collected and pooled into a collection
container, with the final collection taking place at the very end of that period.

Blood specimens:

There are three types of blood specimens commonly used in the clinical chemistry laboratory.
These are:

• Whole blood.

• Serum.

• Plasma.

The whole blood comprises of plasma, serum, white blood cells and red blood cells. The type
of the test determines which specimen should be used.

Main differences between serum and plasma:

• Serum is the supernatant fluid when coagulated blood has been centrifuged. The blood is
allowed to clot at room temperature for 15 to 30 minutes then centrifuged.

• Plasma, on the other hand, is the supernatant fluid obtained when anti-coagulated blood has
been centrifuged. The blood is mixed with an appropriate amount of anticoagulant like heparin