Are your indirect and direct analysers well correlated normally?
We have seen this phenomena recently in samples from the ITU. Our direct ISE
is 'correlated' to flame results ie a fiddle factor (about x0.92)has been
introduced to lower the results. This works fine for patients with normal
protein/lipid levels. But in patients with hypoproteinaemia the correction
factor does not apply and the direct results are lower than they should be
because the factor is overestimating the amount of volume exclusion present.
At the same time because the plasma becomes more like water the indirect
result is higher (due to the decreased dilutional effect). Add these two
effects plus a bias between the direct and indirect analysers and you can
start to get large differences between the machines. The effect of volume
expanders appears to depend on which expander solution has been used.

I must admit though the highest difference we have seen is about 15mmol/L.

Ian Mc


>From: "Hogan, Tim" <[log in to unmask]>
>Reply-To: "Hogan, Tim" <[log in to unmask]>
>To: [log in to unmask]
>Subject: Unexplained results
>Date: Wed, 23 Jan 2002 17:28:58 -0000
>
>We recently received a blood sample taken from a six year old boy who
>attended our phlebotomy Dept.  His clinical details were recurrent cough
>and
>abdominal pains with possible weight loss, he was not on a drip.
>The sample was taken into a disposable 5ml syringe and then transferred to
>a
>small plastic Lithium heparin tube for Chemistry and an EDTA for
>Haematology.
>The patients results which were very abnormal are listed below. The results
>were phoned to the GP and the patient was admitted to the paediatric ward a
>few hours later and another blood sample taken. The results for which were
>normal.   This same situation occurred about a month ago but on an adult
>patient who was on plasma expanders and the samples taken into 7ml Beckton
>Dickenson SST tubes.
>
>The original sample appears diluted but with a high Sodium which is not
>detected (or not so detected) by Direct ISE. The high Sodium is repeatable
>on two different Olympus AU600 (indirect ISE) analysers. The Haematology
>sample also showed similar dilution effect. Has anyone any ideas what could
>be causing this effect?
>         Original         Original        Direct ISE      Repeat
>         Analyser A       Analyser B             sample
>Na       173     171     148     140
>K        3.2     3.2     2.7     3.7
>Urea     3.6                    6.1
>Glucose  2.9                    4.8
>Creat    46                     62
>Calcium  1.34                   2.5
>Albumin  31                     46
>TP       51                     70
>ALT      12                     12
>ALP      128                    187
>Bilirubin        4                      3
>Osmolality       275                    289
>Hb       8.3                    11
>WCC      7.2                     13.1
>platelets        411                    570
>HCT      25%                    32%
>RBC      3.1                    4.1
>MCV      80                     78
>
>
>   Tim Hogan
>Basildon
>
>
>
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