LABLink
ISSUE
11
FEBRUARY
2016
Calgary Laboratory Services Pathology & Laboratory Medicine Newsletter
this issue
Cortisol assay change P.1
Improving aspartate aminotransferase utilization P.2
Fecal fat ordering for adults P.4
Cortisol Assay Change
Richard Krause, Ph.D. DABCC, Clinical Biochemist, DSC; [email protected]
Alex Chin, Ph.D. DABCC FACB, Clinical Biochemist, DSC; [email protected]
Isolde Seiden Long, Ph.D. DCC FCACB DABCC, Clinical Biochemist, FMC; [email protected]
Notifications:
The CLS Fine Needle
Aspiration Clinic operates
bi-weekly on Fridays
(except statutory holidays)
between 1:00 pm and 4:00
pm. at Out-Patient Clinics
Department, Specialty Clinic
2, Peter Lougheed Centre,
3500-26 Ave NE,
Calgary, AB.
For appointment bookings,
please contact the
Laboratory Information
Centre (LIC) at
403-770-3600.
Editor:
Alex C. Chin, Ph.D. DABCC FACB
Key Points:
• As of April 5, 2016, the old cortisol reagent will be discontinued.
• The new cortisol reagent is more specific
and produces results that are 25-30%
lower.
• Results from both old and new reagent
formulations will be reported until April
2016 to assist in interpretations.
As of April 5, 2016 the reagent CLS uses for
the assay of blood cortisol is being replaced.
Because results by the new assay are significantly lower for most patients, both assay
results will be reported until April to assist in
interpretation changes which will be necessary once the old reagent is discontinued.
Please use this transition period to determine
what changes in clinical decision cut-points
will be appropriate in your practice with the
new assay.
This change is necessary because adequate
amounts of the antibody used in the current
assay are no longer available. The reformulated assay is based on a monoclonal antibody;
thus assuring a longer term supply of the
new reagent. The new assay has been standardized against a more recently developed
reference material (IRMM/IFCC 451 Panel IDGC/MS) and will produce results approximately
25% to 30% lower than those of the old assay.
In our laboratory we found the relationship of
the assays to be:
New Assay Cortisol =
(Old Assay Cortisol x 0.7) + 20 nmol/L
The reported reference intervals will be adjusted as follows to reflect the lower results when
the new assay is put in use.
Test
AM Cortisol
PM Cortisol
Old
Reference
Interval
200 – 690
nmol/L
60 – 450
nmol/L
New
Reference
Interval
170 – 500
nmol/L
75 – 285
nmol/L
The new assay shows generally lower crossreactivity to some clinically important similar
molecules.
(Continued next page)
Because of this, individual samples with increased concentrations of cross-reacting substances may produce results with differences between the two assay results not due only to the calibration difference. Listed cross-reactivity of some substances
for the two assays are:
Substance
Corticosterone
Cortisone
11-deoxycorticosterone
11-deoxycortisol
Dexamethasone
17-α-hydroxyprogesterone
Prednisone
Progesterone
21-deoxycortisol
Prednisolone
6-α-methylpredisolone
Old Assay
5.8%
0.3%
0.69%
4.10%
0.08%
1.50%
0.28%
0.35%
45.4%
171%
389%
New Assay
2.48%
6.58%
0.64%
4.90%
None detected
0.08%
2.23%
0.035%
2.40%
7.98%
12.0%
For additional information, please contact Drs. Richard Krause at 403-770-3209 or [email protected], Alex Chin at 403770-3222 or [email protected],or Isolde Seiden Long at 403-944-3993 or [email protected].
Improving aspartate aminotransferase utilization by using alanine aminotransferase as a
prescreen for liver disease
Dennis J. Orton, Ph.D.; Clinical Biochemistry Fellow, [email protected]
Alex C. Chin, Ph.D. DABCC FACB, Clinical Biochemist, [email protected]
Key Points:
• Aspartate Aminotransferase (AST) and Alanine Aminotransferase (ALT) are commonly ordered together to diagnose liver
damage
• AST is a non-specific marker of liver damage, however both AST and ALT are commonly elevated together
• Limitation of AST ordering to those samples with elevated ALT potentially limit unnecessary clinical action
Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) are highly concentrated in hepatocytes, but it is not
clinically useful to measure both markers to screen for liver damage since AST is also highly abundant in red blood cells, heart
and skeletal muscle. Establishment of an abnormal ALT cutoff to evaluate liver integrity before measuring AST may help determine when a follow up AST measurement may be indicated when screening for liver injury and improve utilization of these
tests.
Pre-screening with ALT may reduce unnecessary AST measurments
Edmonton Zone: A recent publication from Cembrowski et al. proposed a reflex testing algorithm be implemented to limit
the number of unnecessary AST tests conducted for patients without liver disease. The proposed algorithm suggested an ALT
cut-off value of 30 U/L (normal range 1 – 60 U/L for adult males, 1 – 40 U/L for adult females) prior to reflex testing for AST.
The study showed they would significantly reduce the number of AST tests done from over 138,000 to less than 41,000 (a
70% reduction in AST workload) in a 15 month period. Furthermore, the study showed that they would miss less than 10% of
elevated AST levels >35 U/L (normal range 8 – 40 for adult males, 8 – 32 for adult females) using the 30 U/L ALT cut-off.
Calgary Zone: Using the same approach, Figure 1 summarizes the effect that employing an ALT cut-off value from 1 – 100
U/L to allow reflex testing for AST would have on workload and missed elevations in AST. Increasing the ALT cut-off value for
reflexing to an AST test has the effect of “missing” high AST values (i.e. an elevated AST would not be detected). Both AST and
ALT values are expected to rise simultaneously, albeit at different rates, therefore the number of AST tests would be reduced
LABLink Issue 11 February 2016
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Community/Outpatient
Hospital/Inpatient
Figure 1 - The blue and red lines plotted on the primary axis demonstrate the proportion of missed AST values exceeding 35 U/L and
50 U/L, respectively for community/outpatient and hospital populations using the ALT cut-off on the x-axis. The green line represents
the proportion of AST not done using the ALT cut-off value plotted on the secondary axis. Data was pulled from September 15, 2014
– September 15, 2015 (12 months) for ALT and AST results reported out from CLS. A total of 820,949 ALT results were reported in this
time, 619,262 of which were from community centres and outpatient labs, and 201,687 from rapid response laboratories (hospital
labs). A total of 68,793 ALT tests were accompanied by an AST result. Of these, 29,424 were from hospital labs and 39,369 were from
community or outpatient labs.
with a higher ALT cut-off value, although more high AST results would be missed. Raising the ALT cut-off value up to 100
U/L would reduce the current AST tests to less than 10% of current workloads, though doing so would miss up to 22% of
AST levels greater than 35 U/L. Setting the threshold for ALT ordering to 30 U/L, as suggested by Cembrowski, et al. would
result in a 64% decrease in AST workload and miss < 5% of elevated AST values (Table 1).
Table 1 - Effectiveness of setting 30 U/L as the ALT cut-off for initiating AST testing
Patient Group
Community/
Outpatient
Rapid Response
Lab
Total
Total AST Not
Done, No. (%)
Elevated ASTs Missed, No. (%)
>35 U/L
>50 U/L
26,343 (66.9)
929 (2.4)
210 (0.5)
17,904 (60.9)
1,929 (6.6)
683 (2.3)
44,247 (64.3)
2,858 (4.2)
893 (1.3)
Use of ALT in practice
AST has a much shorter half-life than ALT in circulation (17 hours versus 47 hours, respectively), making ALT persist longer
in circulation than AST. The relatively short half-life of AST can be used to aid in diagnosis of the cause of liver damage by
using the AST/ALT De Ritis ratio. With acute liver damage, an elevated AST result will yield a De Ritis ratio >1. Since ALT persists longer in circulation and with the chronic nature of most cases of liver disease, the De Ritis ratio will be <1 except for
alcoholic hepatitis, hepatic cirrhosis, and liver neoplasia. Chronic alcoholics exhibit a consistently elevated AST value over
ALT, leading to an extremely high De Ritis ratio > 2 in many cases. This is due to constant liver damage causing additional
release of mitochondrial (in addition to cytoplasmic) AST, reduction of ALT content of the liver, and nutritional and metabolic deficiency in pyridoxal-5’-phosphate (vitamin B6) which is a cofactor required for both ALT and AST activity in vivo as
well as laboratory measurement in vitro. Although both AST and ALT are useful in differentiating between liver diseases,
general screening should not employ both AST and ALT due to the lack of specificity of AST. The data above indicates that
ALT cannot completely predict the AST level, but it demonstrates that AST utilization can be improved and that a good
patient history, particularly noting alcohol use, should precede AST ordering.
Reference
Xu, Q, Higgins, T, Cembrowski, GS. (2015) Limiting the Testing of AST: A Diagnostically Nonspecific Enzyme. Am. J. Clin.
Pathol. 144:423-426.
LABLink Issue 11 February 2016
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Changes to quantitative fecal fat ordering for adults
Jessica Boyd, Ph.D., Clinical Biochemist, DSC, [email protected]
Lawrence de Koning, Ph.D DABCC FACB, Clinical biochemist, ACH, [email protected]
Key Point:
• The 72 hour Quantitative Fecal Fat Test is generally not an appropriate test for diarrheal investigations in adults and will be
available to adult patients (18 years and older) only through approval by CLS biochemist (Dr. de Koning).
• Specimens received without pre-approval will not be run, and a qualitative microscopic test for fat globules (STFAT) will be
run instead.
• Testing frequency is once / month. Alternative tests are available with daily or weekly turnaround.
Background
Since 1949, the 72-hr quantitative fecal fat test has been used to diagnose steatorrhea due to fat maldigestion or malabsorption.
However the use of other laboratory tests and careful review of clinical information has largely made this test obsolete. In addition, this test poses significant challenges for both the patient and clinical laboratory.
Patient challenges
The test requires adults to follow a high fat diet (100g/day) for 5 days, providing sufficient fat for diagnosis of fat maldigestion
or malabsorption. During this period, patients are required to record what they eat in a diet diary to self-monitor compliance. In
the final 3 days (72 hr), patients collect all stool in empty paint cans and submit them to the laboratory.
As expected, patient compliance is poor. Collections of less than 72 hours are common, which may not be suitable for estimating
long-term fat excretion. Patients may also not adhere to the requirements of the high fat diet, leading to false negative results.
Laboratory challenges
The test is manual, and involves the saponification of stool fats with strong base, acidification and extraction in ether followed
by titration with strong base to determine fatty acid content. These steps present significant chemical and biosafety hazards to
lab staff. Further, the test requires the attention of one medical laboratory technologist for 8 hours to test 7 patient samples, and
is only run once every two weeks. Compared to other clinical laboratory tests, this test is very imprecise (maximum total error =
22%) and the quality of results are not monitored by external programs (e.g. College of American Pathologists Proficiency Testing Surveys). While this test is often ordered to assess the causes of diarrhea in adults, fecal fat content increases with diarrhea
even in healthy individuals - falsely elevating the results of this test. Particularly in adults, chemical fecal fat measurement does
not aid in diagnosis or management of the patient and other laboratory investigations should be considered. Furthermore, patient diet records for adults in Calgary are not processed to yield total fat intake. This complicates the interpretation of this test
as fat malabsorption is harder to recognize without information on dietary fat intake. In Children, diet records are processed and
fecal fat output is reported as % fat excretion.
Alternatives
Qualitative microscopic assessment of fat globules in stool is offered by CLS. Samples are stained with Oil Red O which stains
dietary fats, but not phospholipids that are released from sloughed intestinal epithelial cells. Samples are examined microscopically for the number of fat globules per field. Samples with greater that 5 globules per high powered field are reported as having excess fat globules. This test can be performed on a random stool sample, making it a much easier collection for patients.
The sensitivity and specificity of qualitative stool microscopy methods for fat malabsorption or maldigestion varies, however
the presence of fat globules in stool combined with clinical symptoms are enough to raise suspicion for fat malabsorption/
maldigestion. A research project at Alberta Children’s Hospital is currently underway to develop and implement a quantitative
microscopic method for assessing fecal fat globules at CLS that will favourably compare to the 72-hr quantitative fecal fat test.
In 2001, Hill et all recommended the following tests in place of the quantitative fecal fat test for different clinical scenarios (Table
1). Most are offered by CLS, or can be obtained by sending specimens to external laboratories.
For further information, please contact Dr. de Koning at [email protected] or 403-955-2277.
References
Hill. P.G. (2001) Faecal fat: time to give it up. Ann Clin Biochem (38):164-167
Van De Kamer JH, et al. (1949) Rapid method for the determination of fat in feces. The Journal of biological chemistry. 1949;177:347-355
Fine, K.D., and Ogunju, F. 2001. A new method of quantitative fecal fat microscopy and its correlation with chemically measured fecal fat
output. Am J Clin Pathol 113: 528-534.
LABLink Issue 11 February 2016
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Table 1 - Alternatives to quantitative fecal fat testing
Clinical scenario:
Abdominal pain, weight loss, diarrhea possible small bowel problem
Floating, light-colored, offensive smelling
stools - steatorrhea
Elderly patient with weight loss - possible
malabsorption
Pancreatic insufficiency, patient on enzyme replacement
Celiac disease screen (CELIAC) or small bowel radiology
None (demonstrating fat malabsorption will not
provide a diagnosis)
Fat intake may be too low – use other investigations
indicated in this Table.
Monitor stool consistency and clinical response
(weight gain), may occasionally need to asses fat absorption (Stool for fat – STFAT, Fecal fat 72 hr - FECAL)
Pancreatic function test (Fecal elastase - ELAST)
Abdominal pain, weight loss - possible
pancreatic insufficiency
Child with foul stool, possible malabsorp- May sometimes need to confirm presence of fat
tion
globules in stool (Stool for fat – STFAT)
Investigating common causes of diarrhea:
Lactose intolerance
Lactose tolerance test - blood (LTT)
Hydrogen breath test for lactose intolerance - (HBT*)
Bacterial overgrowth
Hydrogen breath test for small bowel bacterial
over¬growth – (HBT*)
Laxative abuse
Laxative screen (send out test; requires approval by
Clinical Biochemistry Medical/Scientific Staff )
Bile acid malabsorption
Bile acids - (BILE)
Secretory or osmotic diarrhea
• Stool sodium (STNA), potassium (STK)
• Calculate fecal osmotic gap
• 290-(2*(Na + K)); < 50 suggests osmotic diarrhea
Fat malabsorption
Fat globules in stool (Stool for fat – STFAT)
Other investigations:
Protein losing enteropathy
Alpha-1-antitrypsin, stool (STAAT)
Gastrinoma / Zollinger-Ellison syndrome Gastrin (GAST)
VIPoma / Verner-Morrison syndrome
Vasoactive intestinal peptide (VIP)
*Hydrogen Breath Tests require referral to Gastroenterology
DID you know. . .
CLS offers the following services to assist
patients with their busy lives?
Appointments
for all patients at all the PSCs
If you would like to
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Department:
which can be pre-booked at least a day in advance
[email protected]
this service and provide the required documentation.
Standing order service:
Second language support services :
for those patients for whom English is not their first
language
for patients who
require blood work on a regular basis. This service
enables patients to drop into any PSC where their lab
work requests are on file electronically thereby avoid-
Free parking at
Service Centres
most
Patient
ing the need to visit their physician each time to obtain
a requisition. Physicians notify the Standing Orders
Office as to which of their patients should be added to
To find out if you fit within the guidelines, contact your
physician directly for further information.
LABLink Issue 11 February 2016
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