Version 1.0
19 Feb 2020
Disclaimer:
This infographic is not a validated clinical decision aid. This information is provided without any representations, conditions, or warranties that it is
accurate or up to date. BMJ and its licensors assume no responsibility for any aspect of treatment administered with the aid of this information. Any reliance placed
on this information is strictly at the user's own risk. For the full disclaimer wording see BMJ's terms and conditions:
http://www.bmj.com/company/legal-information/
© 2020 BMJ
Publishing G
r
oup
L
td.
Y
our
r
esults may
v
a
r
y
A tool
f
or visualising the
v
ariability of lab test
r
esults
Inte
r
acti
v
e
Interpreting results can be challenging for patients and clinicians
alike. Results can be affected by measurement uncertainty, and by
variation caused by biological processes. This tool (based on data in
the article below) is designed to help you decide if two consecutive
results can be considered truly different after these kinds of
variation have been taken into account.
1
Choose a test
2
3
4
Adjust
v
ariables
Enter lab
r
esults
View estimates
These b
o
x
es a
r
e automatically
populated with
r
easonable
estimates of the analytic
v
ariation
(autho
r
s’ lab) and biologic
v
ariation (published
r
esea
r
ch).
These can be adjusted as needed.
Analytic
v
ariation
Biologic
v
ariation
Confiden
c
e
l
ev
el
Normal
r
ange
(
r
e
f
e
r
en
c
e inte
r
v
al)
Low
High
Enter one o
r
,
if a
v
ailable, t
w
o
serial lab
r
esults
The minimum change
r
equi
r
ed to
c
onclude that t
w
o serial measu
r
ements a
r
e likely di
ff
e
r
ent is called the
"
r
e
f
e
r
en
c
e change
v
alue" (
R
CV). Ar
r
o
w
s to the left and right of
y
our fi
r
st
r
esult sh
o
w the
R
CV
f
or this test.
F
or serial
r
esults, measu
r
ements can be
c
onside
r
ed di
ff
e
r
ent if the se
c
ond is outside the
R
CV of the fi
r
st.
Potassium (mmol/L)
95%
Potassium (mmol/L)
Normal
r
ange
Outside normal
r
ange
Result 2 is within the RCV, so the difference
may be due to the combined eff
ects
of analytic and biological variation
Result 2 is outside the RCV, so the difference
is unlikely to be due to the combined effects
of analytic and biological variation
4.6
3.3
4.5
3.9
>
R
esult 1
R
esult 2
Show
The g
r
een shaded a
r
ea
r
ep
r
esents the
r
e
f
e
r
en
c
e inte
r
v
al
of this test, as p
r
o
vided ab
ov
e.
T
ypically 95% of healthy
individuals
w
ould be
e
xpected to ha
v
e a test
r
esult within
this
r
ange and 5% of healthy individuals
w
ould be
e
xpected to ha
v
e a test
r
esult outside this
r
ange.
Normal
r
ange
Serial lab
r
esults
r
e
f
e
r
s to t
w
o measu
r
ements made
ov
er
a period of time
r
ather than simply a
r
epeat measu
r
ement
per
f
ormed to
c
onfirm an initial measu
r
ement
Measu
r
ement timing
The
r
e is alwa
y
s some un
c
e
r
tainty a
r
ound the
r
esult of any
clinical lab test. This kind of
v
ariation can be a
ff
ected by:
The de
f
aut
v
alues p
r
o
vided he
r
e a
r
e calculated as
described in Appendix 1, and a
r
e li
k
ely similar in most
up-to-date hospital labs. This
v
alue can be adjusted if needed,
with data f
r
om a local labo
r
ato
r
y
.
Analytic
v
ariation
Pipetting er
r
or
R
eagent deterio
r
ation
Con
c
ent
r
ation being measu
r
ed
Calib
r
ation drift
Human
f
acto
r
s
When
r
epeated measu
r
ements a
r
e made
ov
er time in an
individual, normal ph
y
siological p
r
o
c
esses
r
esult in biological
v
ariation.
V
alues can be a
ff
ected by:
The
v
alues used in this tool a
r
e deri
v
ed f
r
om lite
r
atu
r
e at the
time of publication, but
v
alues can be adjusted if needed in
light of fu
r
ther in
f
ormation be
c
oming a
v
ailable.
Biologic
v
ariation
Ph
y
siology
Diet
Activity
S
t
r
ess
Mood
W
eather
/
climate
S
tate of health
Living envi
r
onment
The
v
alues p
r
o
vided sh
o
w an
e
x
ample of the normal
healthy
r
ange
f
or a
y
oung adult
f
emale. These a
r
e
p
r
o
vided
f
or
r
ough guidan
c
e only and should be
r
epla
c
ed by those of
y
our local labo
r
ato
r
y as
f
ound
on the clinical
r
epo
r
t. Di
ff
e
r
ent
r
anges may apply
f
or
patients at different stages of life or with di
ff
e
r
ent
cha
r
acteristics, such as:
R
e
f
e
r
en
c
e inte
r
v
al
Age
Gender
E
thnicity
Age
Gender
E
thnicity
Pube
r
ty
P
r
egnancy
Menstrual C
y
cle
Menopause
The
c
onfiden
c
e l
e
v
el - the l
ev
el
of p
r
obability
f
or di
ff
e
r
en
c
es
bet
w
een
r
eadings - is set to
95% by de
f
ault. This can be
adjusted if needed.
Confiden
c
e l
e
v
el
Please enter a number
Please enter a number, or leave blank
Please enter a number
Please enter a number
Please enter a number
Please enter a number
Low value should probably be lower than the high value, no?
99%
95%
90%
85%
80%
75%
70%
65%
60%
55%
50%
25-hydroxy-Vitamin D
Alanine Aminotransferase
Albumin
Alkaline Phosphatase
Aspartate Aminotransferase
Calcium
Chloride
Creatinine
Gamma Glutamyltransferase
Glucose
HbA1c Diabetes IFCC
HbA1c Diabetes NGSP
HbA1c Healthy IFCC
HbA1c Healthy NGSP
HDL Cholesterol
Hemoglobin
Holotranscobalamin
Iron
Lactate
Lactate Dehydrogenase
LDL Cholesterol
Magnesium
Osmolality
PCO2
Phosphate
Potassium
Rheumatoid Factor
Sodium
Thyroid Stimulating Hormone
Total Bilirubin
Total Cholesterol
Total Protein
Total Testosterone
Transferrin
Triglycerides
Urea
Uric Acid
Vitamin B12
*
*
*
*
*
Reference change values for HbA1c differ according to whether the patient has diabetes and whether
IFCC or NGSP units are used