Common Collection Errors
Avoiding Common Collection Errors
Careful attention to routine procedures can
eliminate most of the errors outlined in this section. Materials provided by the
laboratory for specimen collection can maintain the quality of the specimen only
when they are used in strict accordance with the instructions provided. To
ensure a sufficient quantity of each type of specimen indicated for the
procedures to be performed, please consult the volume requirements published in
General Collection Errors
Some of the common errors affecting all types of
Failure to label a specimen correctly and to provide
all pertinent information required on the test request form. (See
Chemistry and Hematology - Blood Collection/Transport Containers.)
Insufficient quantity of specimen to run test or QNS
(quantity not sufficient). (See
Quantity Not Sufficient.)
Failure to use the correct container/tube for
appropriate specimen preservation.
Inaccurate and incomplete patient instructions prior
Failure to tighten specimen container lids,
resulting in leakage and/or contamination of specimens.
Serum Preparation Errors
The most common serum preparation errors include:
Failure to separate serum from red cells within 60
minutes of venipuncture.
Failure to allow the specimens to clot before
Preparing Serum on clotting and serum-separator tubes and red-stopper
Hemolysis: red blood cells break down and components
spill into serum. Causes and prevention are discussed under the section on
Lipemia: cloudy or milky serum sometimes due to the
patient's diet (discussed under the section on lipemia).
Plasma Preparation Errors
The most common errors in the preparation of plasma
Failure to collect specimen in correct additive.
Failure to mix specimen with additive immediately
Hemolysis or damage to red blood cells breakdown.
Incomplete filling of the tube, thereby creating a
dilution factor excessive for total specimen volume (QNS).
Failure to separate plasma from cells within 30-45
minutes of venipuncture for those specimens requiring this step.
Failure to label transport tubes as "plasma".
Failure to indicate type of anticoagulant (eg,
"EDTA", "citrate", etc.
Urine Collection Errors
The most common urine collection errors include:
Failure to obtain a clean-catch, midstream specimen.
Failure to refrigerate specimen or store in a cool
Failure to provide a complete 24-hour
collection/aliquot or other timed specimen.
Failure to add the proper preservative to the urine
collection container prior to collection of the specimen.
Failure to provide a sterile collection container
and to refrigerate specimen when bacteriological examination of the specimen is
Failure to tighten specimen container lids,
resulting in leakage of specimen.
Failure to provide patients with adequate
instructions for 24-hour urine collection.
Failure to divide specimen into separate containers
for tests with such requirements.
In general, grossly or even moderately hemolyzed
blood specimens may not be acceptable for testing. Hemolysis occurs when the red
cells rupture and hemoglobin and other intracellular components spill into the
serum. Hemolyzed serum or plasma is pink or red, rather than the normal clear
straw or pale yellow color.
Grossly hemolyzed samples will be rejected. A sample visibly hemolyzed will be rejected for the following analytes:
Acid Phosphatase, Alkaline Phosphatase Isoenzymes, Alkaline
Phosphatase, Amylase, Amylase Isoenzymes, ALT, AST, Bilirubin, CK Isoenzymes,
CK-MB, CPK Folate, Glucose, Lipase, LDH, LDH Isoenzymes, Phosphorous, Potassium,
RPR, Type and Crossmatch, Type and Screen, VDRL(CSF), Alpha-fetoprotein.
Hemolysis can be caused by:
Most cases of hemolysis can be avoided by
observing the steps listed.
For routine collections, use a 20- to 22-gauge
needle. (On occasion, however, it may be necessary to use a 23-gauge needle for
patients from elderly and pediatric populations with small or difficult veins.)
If there is air leakage around the needle or loss of
vacuum in the tube, replace the vacuum tube.
If you are using your own collection equipment
instead of the vacuum tube technique, use only clean, dry, sterile needles,
syringes, and tubes.
Collect blood in room temperature containers unless
the specimen requirement specifies otherwise.
When there is difficulty accessing a vein or when a
vacuum tube fills too slowly due to a difficult venipuncture, damage to the red
blood cells may result. Correct by collecting a fresh tube when blood flow is
established or select another puncture site and, using sterile/unused equipment,
collect a second specimen. Also, a blood pressure cuff will reduce trauma to
fragile red blood cells.
Do not remove the needle from the vein with the
vacuum tube engaged. This applies to both the last tube collected during a
routine venipuncture and to tubes collected during a difficult procedure.
Premature removal of the tube causes a rush of air
to enter the tube, which may result in damage to the red cells.
Be as gentle as possible, drawing the blood evenly.
Too much pressure in drawing blood into a syringe or forcefully ejecting blood
into a collection tube from a syringe may damage red cells.
Allow collection site to dry after cleaning. Alcohol
used to clean the puncture site may cause contamination in a tube.
Do not collect a specimen in a hematoma.
Allow specimen to clot completely before
Do not centrifuge the specimen for a prolonged
period of time.
Proper Collection of
Tubes with Anticoagulant
(eg, anticoagulants, preservatives, clot
activators). When using vacuum tubes containing an additive:
Blood collection tubes with anticoagulant should be
inverted gently as soon after collection as possible to prevent clotting. All
blood collection tubes must be filled to the fill line in order to prevent
dilution of blood components. Tubes with anticoagulant improperly filled will be
Deliver the samples to the laboratory promptly.
Valid measurement of analytes in serum or plasma requires prompt separation from
the blood cells and analysis in the laboratory. When left unseparated, analytes
shift between the cells and the plasma or serum and glucose, is consumed. In
addition, some analytes are unstable at room temperature. Microbiology specimens
require specific preservation methods according to body site. Refer to specific
test for details.
Tap the tube gently at a point just below the
stopper to release any additive adhering to the tube or stopper.
Permit the tube to fill completely to ensure the
proper ratio of blood to additive. There will be some dead space at the top of
To ensure adequate mixing of blood with the
anticoagulant or preservative, use a slow rolling wrist motion to invert the
tube gently five or six times. Failure to invert tubes may lead to the formation
of microscopic clots. Rapid wrist motion or vigorous shaking may
contribute to hemolysis.
Check to see that all the preservative or
anticoagulant is dissolved. If any preservative powder is visible, continue
inverting the tube slowly until the powder is dissolved.
If multiple samples are being drawn, invert each
specimen as soon as it is drawn. Do not delay. Place the tube upright in a rack
as quickly as possible after collection.
serum-separator tube is an additive tube and should be inverted five to six
times after collection. Allow the tube to stand 15-30 minutes for complete
clotting to occur prior to centrifugation.
Vacuum Tubes without
When using vacuum tubes containing no additives:
Permit the tube to fill completely.
Let the specimen stand for a minimum of 30 minutes
and not longer than 60 minutes prior to centrifugation. (CLSI Guidelines
recommends no more than 2 hours.) This allows time for the clot to form. If the
specimen is allowed to stand for longer than 60 minutes, chemical activity and
degeneration of the cells within the tube will take place, and test results may
Centrifuge the specimen at the end of the waiting
period in strict accordance with the manufacturer's instructions for speed and
duration of centrifugation (usually 10-15 minutes).
Inadequate mixing of the vacutainer tubes as soon as
possible after the phlebotomy will result in the blood not mixing with the
anti-coagulant. By gently inverting the vacutainer tube 4-10 times, the
blood will mix and clotting will not occur.
Quantity Not Sufficient
One of the most common and expensive errors in
specimen collection is the submission of an insufficient volume of specimen for
testing. The laboratory sends out a report marked QNS (quantity not sufficient),
and the patient has to be called back for a repeat collection at additional
expense and inconvenience to the patient and to the physician. To ensure an
adequate specimen volume:
Always draw whole blood in an amount 2½ times the
required volume of serum required for a particular test.
For example, if 4 mL of serum are required, draw at
least 10 mL whole blood. If there is difficulty in performing venipuncture,
minimum volume may be submitted if it is indicated in the test description. For
most profile testing, draw at least two 10-mL serum-separator tubes. If
pediatric tubes are used, be sure to collect an adequate volume of specimen to
perform the test.
Provide patients with adequate containers and
instructions for 24-hour urine and stool collections.
For most serum and plasma tests, check to be certain
that the transport tube is half full. Note: Certain tests (eg, prothrombin time)
require a 90% to 100% full tube in order to achieve the proper
blood-to-anticoagulant ratio; otherwise, the specimen may be found to be QNS.