Post on 16-Dec-2015
Sampling
Contents:
• Specimens used for analysis
• Factors affecting the results of blood samples
• Precautions for collecting blood specimens
• Collection of Urine Specimens
SamplingSpecimens used for analysis include:
1 .Blood.
2 .Urine.
3 .CSF.
4 .Fluids obtained by tapping Pleural
Peritoneal
Pericardial
Synovial
5. Amniotic Fluid.
6. Gut Secretions : Gastric
Intestinal 7. Sweat.
8. Saliva.
9. Calculi : Renal
10. Feces. Biliary
11. Bile.
Specimens obtained must be:
• Properly labeled for identification.
• Of good quality e.g. No hemolysis in blood.
• Suitably preserved anticoagulant
refrigeration
others e.g. ice bath
Factors affecting the results of blood samples:
The most important points to bear in mind
while collecting blood samples are :
• Relation to diet
• Relation to drugs
• Relation to day time
Carbohydrate meal Bl. Glucose
Diet Protein meal Urea
Fat meal marked TG
little Cholesterol
Drugs
Oral contraceptives containing estrogens
Cortisol
T3, T4
HDL-Cholest.
TG
Therapeutic Drug Monitoring
Few to several hours after last dose.
Just before next dose
Glucose Tolerance
Diurnal variations : Cortisol am. pm.
Precautions for collecting blood specimens:1. Blood is an infectious agent.
2. Condition of the patient :
Completely relaxed
Physically (no exertion)
Mentally (allay apprehension)
30 min before
collection
Specially important for
Cortisol
Blood gases
Lactate
3. Posture of the patient:
Lying down for 20 min,
recommended for :
Plasma proteins & substances bound to them
( Ca, T3 &T4, Cortisol, Lipids)
by standing up
(redistribution
of body fluids)
by standing up
(Renin)
Aldosterone
4 .Choice of vein:
• Choose a wide vein even if palpable but not visible.
• Never collect blood from a vein in which an IV infusion is being given, even if distal to the infusion site.
5 .Cleansing of skin: Ethanol ( Not to be used if ethanol in blood is
70 % to be determined )
Isopropanol
6 .Venous Stasis:
Should be minimal
specially for:
Plasma proteins
Lactate
Coagulation Studies
Ca, Cortisol, T3&T4 , Lipids
7 .Avoid Hemolysis:
• Alcohol used for cleansing, should dry before
needle introduction.• Choice of wide vein.• Minimal venous stasis.• Clean introduction of needle into vein.• Moderate drainage of blood.• If you are using syringe for drainage, remove
the needle before delivery of blood into the tube.• Gentle mixing with the anticoagulant.
Effects of Hemolysis:
• Electrolytes : K & Mg
• Proteins E/P : -globulin
• Enzymes : LDH other enzymes e.g. AST
• May interfere with some tests
8 .Care of sample after collection: -Blood gases
-Lactate
-Pyruvate
Rapidly process the blood sample OR keep in ice bath until analysis
- Generally , separate plasma or serum as soon as possible, if not, the following changes may be observed:
a) Glucose lactate, except if collected on fluoride
b) Some substances may leak from RBCs K, LDH & P
c) Loss of CO2 & giving of O2
d) Certain enzymes are labile e.g. Acid phosphatase
Collection of Urine Specimens:• Many measurements may be done on a random
sample.
• A better value is obtained if measurement is done on a timed collection of urine e.g. 24-h sample:
1. Start at 8.00 h by completely emptying the bladder, this urine is discarded.
2. Thereafter, collect all urine voided into a container which is kept in the refrigerator. An alternative is to add a suitable preservative to the container and to mix it well with the urine each time the urine is added.
3. At 8.00 h next day urine is voided and added to the urine collected.