Techniques In Biochemistry Lab.pdf

Chapter 1

The Clinical Biochemistry Laboratory the use and the

requirements of laboratory

Objective of the session

To make the students aware of the basic setup of laboratory, the

procedure for sample collection, separation to the analysis.

Introduction :

Clinical Biochemistry tests comprise over one third of all hospital laboratory

investigation. clinical biochemistry is that branch of laboratory medicine in

which chemical and biochemical methods are applied to the study of disease

while in theory this embraces all non-morphological studies, in practice it is

usually, though not exclusively, confined to studies on blood and urine

because of the relative ease in obtaining such specimens although analysis

are made on other body fluids such as gastric aspirate and cerebrospinal

fluid.

The use of Biochemical tests :

Biochemical investigations are involved, to varying degrees, in every branch

of clinical medicine.

• The results of biochemical tests may be of use in diagnosis and in the

monitoring of treatment.

• Biochemical tests may also be of value in screening for disease or in

assessing the prognosis once a diagnosis has been made (fig. 1)

• The biochemistry laboratory is often involved in research into the

biochemical basis of disease and in clinical trials of new drugs.

Treatment

Diagnosis

Biochemistry

Report

Sugar Î110mg/dl

Urea Î 62mg/dl

Creatinine-1.8mg/dl

Screening

Prognosis

Fig. 1 How Biochemical Tests are used

The use of the laboratory :

Every biochemistry analysis should attempts to answer a question which the

clinician has posed about the patient obtaining the correct answer can often

seem to be fraught with difficulty.

Basic steps for drawing a blood specimen

Preparation for blood collection.

(A) The information given on the blood request form should be

recorded on the specimen labels essential items include the

following.

Patients complete name and age.

Identification number.

(B)

The specimen containers should be labeled appropriated

before the specimen collection.

Ascertaining whether the patient to fast such care is needed to

ensure accurate results.

The technician must gain the patients confidence and assure him

that, although the venipuncture will be slightly painful, it will be

short duration.

Positioning the patient

(a)

The patient should be made to sit comfortably in a chair

and should position his arm straight from the shoulder

and it should not bent at the elbow.

(b)

If the patient wants to lie down, let the patient to lie

comfortably on the back, the patient should extent the

arm straight from the shoulder.

Requirement of Blood Collection

Collection tubes.

Sterilized syringes and needles.

Sprit or 70% ethanol.

Cotton.

Blood collection :

•

Compare the requisition form and labeling the tubes.

•

Selecting Vein site.

•

Applying the tourniquet.

•

Cleaning the area.

•

Inspecting the needles and syringes.

•

Performing the venipuncture.

Separation of serum :-

Allow the blood to clot.

Loosen the clot slowly and centrifuge the supernatant fluid.

By using a pipette, separate the serum from blood cells and store it in

a clean & day test tube.

Sampling errors

There are a number of potential errors which may contribute to the success

or failure of the laboratory to provide the correct answers to the clinician's

question. Some of these problems arise when a clinician first obtains

specimens from the patient.

• Blood sampling technique. Difficulty in obtaining a blood specimen

may lead to haemolysis with consequent release of potassium and

other red cells constituents. results for these will be falsely elevated.

• Prolonged stasis during venepuncture. Plasma water diffuses into the

interstitial space and the serum or plasma sample obtained will be

concentrated. Proteins and protein-bound components of plasma such

as calcium or thyroxine will be falsely elevated.

• Insufficient specimen. Each biochemical analysis requires a certain

volume of specimen to enable the test to be carried out it may prove to

the impossible for the laboratory to measure everything requested on a

small volume specimen.

• Errors in timing. The biggest source of error in the measurement of

any analyte in a 24-hour urine specimen is in the collection of an

accurately timed volume of urine.

• Incorrect specimen container. For may analyses the blood must be

collected into a container with anticoagulant and preservative. For

example, samples for glucose should be collected into a special

container containing fluoride which inhibites glycolysis; otherwise the

time taken to deliver the sample to the laboratory can affect the result.

If a sample is collected into the wrong container, it should never be

decanted into another type of tube. for example, blood which has

been exposed even briefly to EDTA (an anticoagulant used in sample

containers for lipids) will have a markedly reduced calcium

concentration, approaching zero.

• Inappropriate sampling site. Blood samples should not be taken

'down-stream' from an intravenous drip. It is not unheard of for the

laboratory to receive a blood glucose request on a specimen taken

from an intravenous drip. It is not unheard of for the laboratory to

receive a blood glucose request on a specimen taken from the same

arm into which 5% glucose is being infused. Usually the results are

biochemically incredible but it is just possible that they may be acted

upon, with disastrous consequences for the patient.

• Incorrect specimen storage. A blood sample stored overnight before

being sent to the laboratory will show falsely.

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