g. Additional points to consider:

 Instruments with adjustable setting for different

substances and/or species should be carefully

checked for compliance

 Compare and make adjustments for performance

characteristics as defined by the laboratory and the

manufacturer.

 Make certain species differences are accommodated.

2. Function checks

 a. Appropriate function checks should be made

on all instruments. These are critical operating

characteristics of an instrument, i.e. stray light,

zeroing, electrical levels, optical alignment,

background checks, etc.

 b. Laboratory personnel should recheck and/or

calibrate each instrument daily or once per shift,

prior to patient testing, to ensure that it is functioning

correctly and is properly calibrated. This includes

daily QC.

3. Calibration

 a. Instruments should be calibrated every 6 months

or more frequently if indicated by:

 Manufacturer’s recommendation

 After major service

 QC outside limits or troubleshooting indicates need

 Laboratory determination that volume, equipment

performance or reagent stability indicate a need for

more frequent calibration

 b. After calibration, controls should be run.

4. Laboratory personnel knowledge of equipment and its

use, including, but not limited to:

 a. Linearity differences from possible manufacturer’s

range (human) to animal

 b. Effects to hemolysis, lipemia, icterus, carotenoid

pigments (especially large animals), and different

anticoagulants on each assay

 c. Reportable ranges

 d. Species-specific ranges and reference intervals

 e. Expected abnormal ranges

 f. Common problems encountered with veterinary

samples

 g. Regular instrument maintenance schedule

 h. Replacement of inadequate or faulty equipment

 i. Problem solving procedures, troubleshooting.

D. Quality Control

1. For each run, at least 2 controls should be assayed.

Use of “high” and “low” abnormal controls is

recommended.

2. Maximum length of a run is 24 hours. If the instrument

manufacturer requires more frequent controls,

observe the recommended frequency (i.e. some blood

gas instruments).

3. Verify that the instrument is stable over the “run time”.

During a validation check, controls are assayed more

frequently to establish run time.

4. Establish QC frequency; consider the following:

 a. Test volume (number performed each run on day)

and frequency

 b. Technique dependence of the method

 c. Analyte or reagent stability

 d. Frequency of QC failures

Clinical Chemistry 517

 e. Training and experience of personnel

 f. Cost of QC (increasing frequency adds to cost-pertest).

5. Quality control parameters

 a. Mean, SD and CV should be calculated (minimum

n = 20)

 b. Controls should be assayed in the same manner as

patient specimens

 c. A mechanism should be in place to determine

whether testing personnel follow policies and

procedures correctly

 d. Use of Westgard multirule procedures or other rules

based on QC validation is recommended

 e. Policies and procedures should be written and

available in a laboratory Standard Operating

Procedures (SOP) manual to ensure accurate and

reliable test results

 f. An SOP manual should have clearly marked and

dated entries of current procedures (manufacturer

package inserts are sufficient as long as verified)

and when any changes are made and implemented

 g. QC records should be reviewed frequently to ensure

that when QC values fail to meet the criteria for

acceptability, suitable action is taken

 h. C o n t ro l p ro d u c t s s h o u l d b e p u rc h a s e d

commercially, if possible. If using calibrators as

controls, use a different lot as QC material. If patient

pooled samples are used, establish the mean value

of all analytes (minimum n = 10 to establish a mean)

 i. Monitor results of clinical specimens for various

sources of error by use of parameters such as

anion gap, comparison of test results with previous

submissions from same patient (delta checks), and

investigation of markedly abnormal results (limit

checks).

E. Procedures Manual

1. All procedures currently in use should be included.

Protocols may be organized in manuals and/or stored

in computers, and be written form. They should

contain such information as:

 a. Patient preparation

 b. Specimen collection, processing and handling

 c. Criteria for rejection of specimens

 d. Limitations of and things that interfere with the

method in use

 e. Step-by-step procedures

 f. Reagent preparation or manufacturer

 g. Reference interval

 h. Reportable range

 i. Literature references

 j Reagent labeling: content, storage requirements,

expiration

 k. Laboratory-specific information, such as:

 Identification of instrument used

 Result reporting method

 Actions to take when system is down

 Criteria for specimen referrals to outside laboratories

(“send outs”)

 Quality control procedures

 Documentation of critical values

 Clearly stated and dated entries of procedure

implementation or change.

F. Comparison of Test Results

If the laboratory performs the same test by more

than 1 method or at more than 1 test site, or the

test is sometimes also sent to a referral laboratory,

comparisons should be run at least twice annually to

define the relationships between methods and sites.

Comparison of different test methods for the same

analyte within the laboratory or between laboratories

(if samples are tested in-house and at a referral

laboratory) is recommended. This should be done every

6 months or at a frequency determined by the laboratory

manager. The following steps should be included:

1. Perform a 20 sample or greater comparison using

specimens covering the analytical range.

 a. Group data in an X-Y comparison plot

 b. Calculate slope and intercept by a least squares

method.

2. Laboratory director or qualified personnel should

define acceptable performance limits.

3. If individual test results performed on the same

patient or material do not correlate with each other

(i.e. BUN/creatinine, electrolyte balance), the cause

should be investigated and corrective action taken.

Postanalytical Factors Important in

Clinical Chemistry

A. Computer Entry of Data

Reports should be accurate whether created manually

or electronically, and in a standard format as established

by the laboratory. Established laboratory standards for

uniform reporting should be met.