PRACTICAL CLINICAL BIOCHEMISTRY

BMS262: PRACTICAL CLINICAL BIOCHEMISTRY
Experiment/Exercise 1 Data handling and analysis of quality control (QC)
Learning outcomes
• describe QA/QC.
• understand applications of QA/QC.
• know the various ways that QC data can be presented.
• explain QC performance and how QC can deviate from the expected and to
explain possible reasons for such performance.
A QC serum-based material, for urea was assayed 60 times in the same run to
establish intra/within performance and 60 times on consecutive days to establish
inter/between performance (reproducibility or precision) of the urease method for
urea measurement in blood.
Mean and standard deviation were calculated and were comparable for within and
between runs. From the mean and standard deviation, a range was established. The
mean was 5.10 mmol/L and the range (giving lower and upper limits) was 5.1O
+ 0.15
mmol/L and this corresponds to
2 standard deviations, which was deemed
acceptable for urea measurement.
This QC s~rum was subsequ_ently assayed i~ the same run/essay with patients’
samples daily for 21 days and 1f the result obtained for this QC serum was within the
established range then the labora_tory was confident of the patients’ results. The QC
results for the 21 days are shown
in Table 1.
Table 1: Daily QC urea levels (mmol/L), over 21 days in July as part f . t

QC for urea assay O m erna/
Da 1 2 3 4 5 6 7 8
Result 5.01 5.06 4.98 4.97 5.00 5.01 5.11 5.12 9 5.19 10

5.06 511.11 12 5.10
Oa 13 14 15 16 17 18 19
Result 5.09 5.09 5.11 5.08 5.11 5.12 5.10 520.08
Use the above data (21 days) to I t
Q
Po C for urea in Section A
Section A
This section teaches the various ways of plotting QC data and you need 2 graph
~apers for Levey-Jennings/Shewhart plots and another graph paper for cusum plot
(1.e. 3 graph papers in total).
Levey-JenningslShewhart plots
(i) Take a graph paper and with landscape as the paper orientation, draw a line
in the middle and plot days (1-21 days) on the x-axis. On the y-axis and on the line
which cuts across the middle of the paper, write O(zero) in the middle and lab~I the
y-axis to accommodate
2 SD i.e. the range given above (.± 0.15). The point at
which the x-axis cuts the y-axis is your zero. Plot the points on this graph by first
subtracting the mean from your observed value for each day (Table 1) for the 21
days (x- axis) and plotting the difference.
Table 2: Daily QC urea levels (mmol!L}, over 21 days in July as part of internal
QC for urea assay: daily changes from the mean i.e. 5.10 mmol/L

Dav 1 2 3 4 5 5.11 5.12 5.19 5.06
6 7 8 9 10

Result 5.01 5.06 4.98 4.97 5.00 5.01 Daily -0.09 -0.04 -0• 12 – o-L3 -o- 1 – 0.09 ~. 01 1t- o,0 ‘2… -t-0.09 –0-04-
u_rea
result
miri.us
mean
Dav
11 12 I 13 14 15 16 17 18 19 20 21
Result 5.11 5.10 5.09 5.09 5.11 5.08 5.11 5.12 5.10 5.08 5.09
Daily io.o I 0 c.o I -0-0 / -1-0.0 1 -o.oz +0-0/ -fO.o2 0 o.oz. ~0-0 I
urea
result
minus
mean

(ii) Take a second graph paper and with landsca e th · ·
dra””‘. a line _in the middle and plot days (1-21 days) on ~h as_ _e paper o~1entat1on,
urea value in the middle and label the
~-:~r,‘A’.~~e the mean (5.10 mmol/L) of the
(5.10
0.15). On this graph you plot the ac:~~t’
the lme cutting across the middle of the a . e x axis. On y-axis and on
I urfea values that accommodate
21 days (x-axis). va ue or each day (Table 1) for the

Cusum plot
This graph requires you to first subtract th
for each day for the 21 days. Add this vai9 mean from Y?Ur observed value (Table
1)
(cu~~m) and do this for the 21 days ( ue to the previous day i.e. cumulative sum
posItIve and other negative. see example below). Some values
will be
2
Table 3· C
. · usum data for dail QC
mternal QC for urea assay y of urea, over 21 days in July
as part of
Dav Daily urea QC result (mmol/L)
1
Daily urea result minus mean–Cusum
5.01
-0.09 -0.09
2 5.06 -0.04 -0.13
3 4.98
4
q.. ‘f-=J-
-0.12 -0.25
5 5.oo
,o. 13 -0-3~
6 5-01
–o. I0 -0-4-1’_
-o. o’J
7 5. I I
-0· 51-
,1.0.01 -0•5 b
8 5 · 12- +0 – OZ- ~o-St..1-
9 S · l’l
10
+-O. O’l ‘rS
Ob _. 0. 0’f -0· q,t:f
11 S· I I .f- O· O I -0. 1.1–~
12 5. 10 0 4-8′
13 5 · oGf o.ol o-‘f-1
14 5 · OCf o-ot O-!i-~
15 5. 11 +O•OI
-o-Y–‘1-
16 c::;. oi 0-02-
-o -§_”1
17 S- I I
,f o.o, -0· fr•
18 ~- ,2 ..f-0· 02.- -o -‘r8
19 Ir;
0
o, q..6
20 <-O~
(‘) .ot. o-60
-0· OI
.., 6″L
21 s.04
Take a third graph paper and with landscape as the paper orientation, draw a line in
the middle and plot days (1-21 days) on the x-axis. Your line may not
be in the
middle depending on the magnitude of your negative and positive values. On the yaxis on the line which cuts across the middle of the paper, write O(zero) in the middle
and label the y-axis to accommodate
±. 0.6 mmol/L (or the range of your cusum
values). On x-axis and for each day, plot the cumulative sum as you go along.