NATIONAL AUDIT OF CSF TESTING
In the autumn of 2004 questionnaires were sent out electronically via regional
audit committees to all laboratories who are known to the audit committees.
These were returned as email attachments or as hard copy to me over a period
of months, the last arriving in February 2005. Replies were received from
Northern Ireland, Scotland, Wales and England.
A total of 84 questionnaires were returned, 42 via email and 42 by post. The
answers were collated and are reported here. Not all questions were answered
in every case so the numbers do not always add up to 84.
56 hospitals undertook the analysis of the CSF within their laboratories.
This compares with about 120 laboratories that regularly analyse CSF in the
UKEQAS scheme.
6 hospitals did not offer a service for looking for haem pigments and bilirubin.
Of course there may be many more hospitals who do not offer this service and
did not reply to the questionnaire.
Does your hospital have a CT or MRI scanner?
83 hospitals had access to CT or MRI scanning and 1 did not.
Is access on a 24hr/day basis?
70 hospitals had 24h access, 13 did not.
Neurology beds?
44 hospitals had neurology inpatient beds and 40 did not.
Neurosurgery beds?
18 hospitals had neurosurgery inpatient beds and 64 did not.
Population served
66 hospitals recorded the populations they served. These ranged from 25,000
(should probably have been 250,000) to 2.5 million with an average of 453,000.
CSF analysis
Protein
Protein was measured in 81 biochemistry departments, 2 microbiology departments
and 1 neuroimmunology department.
63 hospitals reported their protein method. 34 used pyrogallol red, 19 benzethonium
chloride, 4 Vitros, 3 “Beckman”, 2 Biuret and 1 Folin Ciocalteau
Protein reference intervals reported ranged from 0-<1.0 g/L but the most
common range was 0.15-0.45 g/L or very similar to this. Many hospitals commented
that they had age-dependent paediatric reference ranges as well.
Glucose
Glucose was measured in 83 biochemistry departments and 1 neuroimmunology
department.
65 hospitals reported their glucose method. 35 used a hexokinase method, 21
glucose oxidase, 5 Vitros, 3 “Beckman” and 1glucose dehydrogenase.
Glucose reference intervals ranged from 1.8-6.5 mmol/L but there was little
consensus. The most popular ranges were 60% of serum level or 2.5-4.5 mmol/L
Spectroscopy
Biochemistry departments mainly performed this test but 1 neuroimmunology
department and 1 neuropathology laboratory also undertook this assay.
Scanning spectrophotometers were used.
Other CSF tests
Other tests mentioned were lactate, oligoclonal bands, IgG and albumin, glycine,
and ACE.
QA schemes used
NEQAS was mentioned by all who filled in this section (bar one hospital who
said they were in the WEQAS scheme).
Visual inspection
25 laboratories visually inspected the CSF, (21 biochemistry, 3 microbiology
and 1 neuropathology department).
Does visual inspection influence whether sample is sent for spectrophotometric
examination?
1 hospital answered yes to this question saying there was no point in scanning
obvious yellow samples. Another hospital answered “yes and no”
to this question but did not elaborate further.
Spectrophotometric scanning – where performed
56 hospitals performed spectrophotometric scans within their hospital, 1 of
these shared this test with neuropathology and another was doing so as part
of training/method evaluation.
22 hospitals sent their samples elsewhere for scanning.
6 hospitals did not offer this service. They served a population of over 2
million. One of these hospitals was planning to introduce the service within
3 months of filling in the questionnaire. They served a population of 620,000.
Sample collection and preparation
SOP for collection?
64 hospitals had an SOP for collection of the CSF, 14 hospitals did not.
How many specimens?
Not all replied to this question but the majority of hospitals asked for 4
samples.
| Specimen | Number of Hospitals |
1 |
4 |
2 |
6 |
3 |
11 |
4 |
46 |
5 |
6 |
Total |
73 |
What type of collection tube?
Most hospitals specified a fluoride sample for glucose and plain sample for
scanning.
Sequential specimens?
Most hospitals requested sequential samples, 16 did not.
Which sample used for scanning?
The majority of hospitals used the 4th or last sample for scanning.
Specimen |
Number of Hospitals |
1 |
2 |
2 |
8 |
3 |
15 |
4 |
37 |
5 |
2 |
Last |
9 |
Total |
73 |
Accept samples not protected from light?
70 hospitals would accept these samples (40 would also add a comment). 7 hospitals
would not accept them.
Accept samples delivered by air tube?
47 hospitals would accept these samples (14 would add a comment). 21 hospitals
would not accept them.
Centrifuge samples prior to analysis?
Every hospital but 2 centrifuged the sample. One of these hospitals would
centrifuge if the sample “was not crystal clear”.
Guidelines for the time of sampling?
69 hospitals had guidelines that recommended sampling at least 12h after the
event (one hospital recommended at least 10h). 8 hospitals did not make any
recommendations. A few hospitals also said the sample should be taken within
1 week of the event and not taken after 2 weeks.
Do you accept samples taken outside these guidelines?
55 hospitals would accept samples taken outside the time guidelines and 42
of these would add a comment. 14 hospitals would not accept a sample taken
outside the time guidelines.
Do you require a simultaneous blood sample?
65 hospitals said they asked for a simultaneous blood sample. The majority
(21) measured bilirubin and protein. 18 measured bilirubin, protein and glucose
and the rest measured a mixture of bilirubin protein and glucose. One hospital
required a blood sample for oligoclonal bands and another for immunoglobulins.
5 hospitals did not specify what they would measure.
12 hospitals did not ask for a simultaneous blood sample.
Number of samples received per year
72 hospitals recorded the number of samples received per year. These ranged
from <5 to 2000 with a mean of 159. If the 2000 entry is removed the mean
is 131.
Sample rejection policies
The reasons for rejection are listed in the table.
Reason |
Number of Hospitals |
| Insufficient | 25 |
| Heavily bloodstained | 17 |
| Unlabelled | 7 |
| Unprotected from light | 6 |
| Less than 12 hours from event | 5 |
| Delivered in pneumatic tube | 4 |
| CT positive | 3 |
| Received more than 1 hour after collection | 3 |
| Visible blood (not for protein or glucose only) | 2 |
| Raised CSF protein or WCC | 2 |
| Clinical symptoms do not concur with SAH | 1 |
| Haemolysed | 1 |
| 2 forms of ID not given | 1 |
| Unlabelled - accept after discussion | 1 |
| Unlikely to reject on any grounds | 1 |
Repeat LP requested?
9 hospitals would ask for a repeat LP but most would qualify the request.
One specified within 2h of the first LP.
Many of those hospitals not asking for a repeat LP gave reasons why they would
advise against it.
Spectroscopic analysis of the CSF
SOP for analysis of the sample?
54 hospitals had an SOP for the analysis. 2 did not.
Literature reference for method
Almost everyone quoted the Guidelines published in 2003 (Ann Clin Biochem
2003; 40: 481-488) or Chalmers’ paper (Clin Chem 2001; 47: 147-148).
One hospital quoted Stroes and Van Rijn paper on derivative spectroscopy (Ann
Clin Biochem 1987; 24: 189-197) and another J Clin Path 2001; 827-830.
Is access limited?
Spectroscopy was available 24/7 is 32 hospitals and “core hours”
only in 24. 11 hospitals qualified the availability out of normal hours by
saying referral to the on-call consultant for the laboratory would be needed.
Is interpretation provided?
All 56 hospitals provided interpretation of the scan.
Is there an SOP for interpretation?
There was an SOP for interpretation in 52 hospitals. 4 hospitals did not have
an SOP for interpretation.
Who interprets the scans?
In 25 hospitals clinical scientists or chemical pathologists or a combination
of the two interpreted the scans. In 19 hospitals interpretation was by a
combination of biomedical scientists, clinical scientists and chemical pathologists.
In 12 hospitals the interpretation was by biomedical scientists.
Absorbance value for full scale deflection
Absorbance values used are listed in the table.
Full scale deflection |
Number of Hospitals |
0.01 |
2 |
0.02 |
1 |
0.08 |
1 |
0.09 |
1 |
0.1 |
26 |
0.2 |
4 |
0.5 |
3 |
1.0 |
4 |
Autoscale |
11 |
Total |
53 |
One hospital did not record their full-scale deflection and 2 hospitals gave
wavelength ranges over which the scan was performed.
Cut-off absorbance value
53 hospitals used <0.007 as the cut-off value that they would report as
negative for bilirubin (one hospital would not use the word “negative”).
One hospital used <0.001 and 2 hospitals did not give a value.
Most replies gave the wavelength as 476nm but 7 gave different wavelengths
(454nm, 470nm, 475nm, and 4 the range 450-460nm).
Report on a scan with oxyhaemoglobin of 0.09AU and no significant bilirubin
41 hospitals reported in line with the guidelines – “Oxyhaemoglobin
present but no significant bilirubin. Oxyhaemoglobin on its own has a low
predictive value for subarachnoid haemorrhage but does not exclude”
or something very similar.
2 reported “present”, 1 reported “negative”. Other
comments included “Our policy of waiting 12h makes this non-applicable”,
“Xanthochromia not detected”, “No comment is made about
oxyhaemoglobin. Reported as CSF bilirubin negative”, “HbO2 only
– most likely traumatic contamination”.
Retention of scans
The table below list how long scans are retained.
Time |
Number of Hospitals |
| 3 months | 1 |
| 6 months | 1 |
| 1 year | 5 |
| 2 years | 12 |
| 3 years | 2 |
| 4 years | 1 |
| 5 years | 4 |
| 7 years | 1 |
| >10 years | 1 |
| Indefinitely | 27 |
| "Years" | 1 |
| Total | 56 |
Many hospitals retained the scans electronically, particularly those that
retained them indefinitely.
Spectrophotometer service
51 hospitals had their spectrophotometers serviced regularly. 5 did not have
them serviced.
Absorption and wavelength checks
45 hospitals checked the absorbance and wavelength regularly. 11 hospitals
did not.
Further information given at the end of the questionnaire
These were all from those samples returned electronically.
“We are very aware of the national guidelines as are our microbiology
colleagues (who do not do visual inspection any more and have told the clinicians
that they are not doing this) and our clinicians.
Currently our clinicians are ‘not interested’ in this. We have
not pushed it because we would need to upgrade spectrometer and would have
difficulty doing 24/7 because of ‘routine’ out of hours workload
per available staff. Unless great pressure, we would resist – unless
clinicians able to fund equipment, etc”
“Excel programme for deriving NBA shown to have better correlation with
manual estimation of NBA from print-out”
“1. The UKNeqas guidelines assume that you get sensible requests e.g.
not from people with known subdural haematoma or severe listeria meningitis
as we have experienced. I feel that they should never say supports SAH without
qualifying it with ‘or other cause of bleed’
2. I feel that you can plot NBA rvs CSF protein and see a relationship which
allows you to see whether a raised CSF protein can account for your observed
NBA given normal bilirubin levels.
3. Quite a lot of reliance is placed on the assumption that with SAH, CSF
proteins tend to be normal, whereas with inflammation they may be abnormal.
I don’t think that this should be used as anything other than a rule
of thumb and should not necessarily influence your comments.
4. You should ALWAYS ask microbiology what they think about their samples!”
“It is sometimes difficult to ensure that the clinicians follow the
guidelines, particularly those from non-neuro specialities”
“We do not utilise the formula for predicting absorbance for adjusting
NBA, for which the evidence base is inadequate. All positive scans are reported
as follows:
‘Spectrophotometric scan of CSF for xanthochromia positive. Caution:
false positive results can occur due to raised CSF protein or hyperbilirubinaemia’
“