POCT for hCG is the area where we seem to have the most "clinical incident
reports" dealt with by Pathology. Getting through to Clinical Staff that it
is not a pregnancy test is the first step. Getting them to look at the whole
clinical picture is the next step. Getting them to use the hCG results as
part of the diagnosis rather than the diagnosis is the next. Using serum
hCG if in doubt is also part of their protocol. Having a good POCT Manager
who can spend time with Clinical Staff explaining the limitations of the
assay and training staff and following up anomalies, is also very useful in
resolving problems. (that sentence is for Chris Royle!)
Most false negatives are difficult to explain, but clinical staff are asked
to keep the urine if in doubt and we then check the hCG using a quantitative
technique in Biochemistry, unfortunately this does not happen very often as
the urine is often in an unlabeled collection pot (and probably someone
elses urine!) so getting to the heart of the problem is difficult
None of the samples that we have checked have been different to the POCT.
"False" positives are more of a problem, including patients bringing other
peoples urine!
Tim Hogan
Basildon.
-----Original Message-----
From: McDonnell, Margaret [mailto:[log in to unmask]]
Sent: 21 December 2005 15:55
To: [log in to unmask]
Subject: Re: ?False negative urine pregnancy results/Christmas Quiz
Assuming there is nothing wrong with the batch or technique, then the
quality of the samples may be another possibility. The manufacturer of
the cartridges that we are about to introduce claim that false negatives
are very rare, but they do suggest some explanations of false negatives;
1.Urine specimens contaminated with blood may affect the fluid flow on
the test strip, producing false negative results. This might be relevant
for your first case.
2.If the patients were catheterized, then the lubricating gel used prior
to catheterisation may also decrease fluid flow on the test strip
(although experience from our current pregnancy test strips shows that
the lubricating gel used by our Trust causes false positive pregnancy
tests).
Margaret McDonnell
-----Original Message-----
From: Clinical biochemistry discussion list
[mailto:[log in to unmask]] On Behalf Of Wills Philip
(Queen Elizabeth Hospital NHS Trust)
Sent: 20 December 2005 17:14
To: [log in to unmask]
Subject: ?False negative urine pregnancy results/Christmas Quiz
I would be grateful for possible explanations for the two
following cases of alleged false negative urine pregnancy
testing results using a well known kit with cut-off 25 U/l.
Please assume there is nothing wrong with the batch. All
obvious actions are underway and the company has been
informed. The kit performs perfectly well in EQA although
this particular batch was not used. Staff in A/E have had
training updated although there is no indication that the
test was not performed correctly.
CASE ONE
Came to A/E with abdominal pain on 9/11/05 and also 12/11/05.
Urine Pregnancy Test in A&E negative on both visits.
Came to A&E again 15/11/05 with abdominal pain
"Just finished period" - 13/11/05(? date of bleed prior to
that.)
Doctor performed a Urine Pregnancy Test approx 08.00h on
15/11/05 (despite 2 recent negatives) which was positive.
Serum beta HCG taken 10.34h on 15/11/05 was 2650 U/l.
The patient had an ectopic pregnancy, which had been missed
on the first 2 occasions. Patient is now doing well.
CASE TWO
Presented 15/11/05. Known to be 8 weeks pregnant. Presented
with hyperemesis, but Urine Pregnancy Test at triage, approx
15.45 was negative. Doctor repeated Urine Pregnancy Test
himself on same sample - again negative. Then asked patient
to provide another sample, which he tested himself, which was
also negative. That is 3 negative tests on 2 samples. Doctor
sent serum beta HCG, approx 16.30h on 15/11/05. The result
was greater than 10000 U/L
No adverse outcome in either case.
PS I have just checked 20 of the "suspect" cassettes against
20 consecutive ex EQA material stored at -20 C and got 100%
correct answers.
Many thanks,Phil Wills
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