A few months ago we had a similar strange false positive: a woman in her
thirties presenting to A/E with abdo pain tested positive with a pregnancy
dipstick. She denied there was any chance she could be pregnant. The sample
was sent to the lab for confirmation. The sample still tested positive with
a urine dipstick (Guest Medical). Fortunately a blood sample was also sent
and was negative. The urine sample was very cloudy and when spun the urine
tested negative by dipstick. A sample was also sent to the Microbiology
lab, where it was reported to have high white and red blood cell count, but
did not grow any organisms.
We have tried to investigate the incident and it is likely that there is
some relation between high white cell count and false positive pregnancy
dipstick tests, (at least that's what we think but we still haven't got to
the bottom of it).
Any chance that this particular patient had a UTI or cloudy urine or
contained precipitates?
Several similar situations have arisen since this time, more recently a 15
year old tested positive but was subsequently shown to be negative, causing
a lot of distress to the patient and family
In addition, a recent NEQAS external Quality assessment sample (December)
indicated that some pregnancy strips in use may show an increased
sensitivity compared to the recommended manufacturers "cut-off "level i.e a
QC specimen with base level of 15 u/l tested positive with most
commercially available kits though the cut-offs were reported as 25 u/l
Angela
Angela Kremmyda
Trainee Clinical Biochemist
Dept of Clinical Biochemistry
Arrowe Park Hospital
Upton, Wirral
CH49 5PE
0151-678 5111 ext. 2830
Fiona Bethell
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Sent by: Clinical Subject: Help - false positive pregnancy tests
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24/07/2007 13:49
Please respond to Fiona
Bethell
48 year old lady is brought to A/E Sunday afternoon after being found
collapsed, pale, nausea, abdo pain.
Assessment shows Hb of 5g/dL and urine preg test positive (Clinitek Status)
but patient with GCS 14/15 says definitely not pregnant. Not catheterised
at time of sample collection ( and have my doubts about lidocaine
interference anyway). Urine not kept.
Drug history nil of note but possessions in bag list
co-codamol/paracetamol/zomig/brufen.
Given blood/FFP/plts and whisked off to theatre but not before to serum
bhCGs (Roche E170) are done and give 1 and 6 U/L. ??reliability if v low
Hb.
Intraoperative notes say no obvious cause for bleed (no AAA/ectopic
rupture)
and given 15 units of blood during op. Another urine arrives and is
positive using Quidel QuikVue one step test so put it through E170 and get
21.5 U/L.
06:30 bloods this morning - bhCG (E170) =2 but ?reliability after massive
transfusion.
What's next?
Fiona
Fiona Ivison
Dept Clinical Biochemistry
Royal Liverpool University Hospital
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