Download Off Schedule Laboratory Tests

PEGASUS HEALTH
GP SMALL GROUP EDUCATION
DIAGNOSTIC DILEMMAS
Diagnostic Dilemmas
Tests covered in this session:





Faecal calprotectin
HLA DQ2/DQ8
Homocysteine
BNP
Vitamin D (a quick look at data)
Case One
Samantha, 34 year old woman:




6/12 diarrhoea
Abdo cramps
Occasional PR bleeding
No weight loss
What else would you like to know?
What are the differential diagnoses?
Case One – Differential Dx








Irritable Bowel Syndrome
Coeliac Disease
Inflammatory Bowel Disease
Lactose Intolerance
Infective Diarrhoea
Endometriosis
Pelvic Inflammatory Disease
Cancer in older patient – Colorectal or Ovarian
What tests (if any) would you order for Samantha?
Faecal Calprotectin Testing
Pros:
 Helps rule out inflammatory causes of diarrhoea
 High negative predictive value
Cons:
 Can be raised in all causes of GI inflammation
(including irritation from NSAID use)
 Many false positives occur
 Also increases with age, inactivity, and obesity
Samantha – 6 Months Later



Sister just diagnosed with coeliac disease
Samantha on gluten free diet last 4/52 with only
slight improvement in symptoms
Requesting blood test for coeliac disease
What do you do now?
Is HLA gene testing appropriate?
Human Leucocyte Antigens & Coeliac
Disease

>99% coeliac patients are HLA DQ2/DQ8 positive
HLA testing has >99% negative predictive value

20-30% general population HLA DQ2/DQ8 positive

•
only 3% of these will develop coeliac disease
HLA genes necessary but not sufficient
for development of coeliac disease
Human Leucocyte Antigens
& Coeliac Disease
Entire NZ Population
30% of Caucasian population will
test positive for HLA DQ2/8
3% of those with a positive
HLA will develop coeliac disease
0.1% of those with negative
HLA will develop coeliac disease
Illustration for Patients
What Role Does HLA Typing Play?

Not diagnostic for coeliac disease (high rate false +ve)

Negative test rules out coeliac disease

IgA tTG is first-line test for Dx coeliac disease


If positive, go back on gluten for 4wks then test IgA tTG
and total IgA
HLA testing not indicated if family history coeliac disease
(~10% prevalence in 1st degree relatives)
Vitamin D Testing
GP count by number of tests
Number of GPs
(9 month period from July 09 – Mar 10)
92
Total number tests = 2911
Number unique patients = 2780
50
41
31
28
14
14
9
1
2
3
4
5
6
7
8
11
10
6
9
10
4
11
12
3
4
13
14
7
6
4
6
6
2
2
2
1
0
1
15
16
17
18
19
20 21-30 31-40 41-50 51-99 100+
Number of tests/GP
Indications for Testing Vitamin D




Atypical osteoporosis
Unexplained raised serum alkaline phosphatase or low
calcium or phosphate
Unexplained proximal limb pain in older people
Unexplained bone pain, unusual fractures or other
evidence suggesting metabolic bone disease

Malabsorption disorders

Long-term anticonvulsant therapy
High risk for deficiency

Consider supplementation for:
 Institutionalised
or house-bound elderly
 People who are veiled
 Very dark skin and little sunlight
 Infants exclusively breastfed by mothers at risk of
deficiency


Cholecalciferol 1.25mg 2 stat then 1 monthly
No requirement for prior testing or monitoring
Case 2 - Homocysteine

Bill, 55yrs, long-term patient, few visits

Recent NSTEMI


Committed to changing his lifestyle to reduce his risk of
another “heart attack”
Wants his homocysteine level tested
What do you know about homocysteine?
Hyperhomocysteinaemia
Has been linked to:
 MI, acute coronary syndrome, recurrent coronary events
 Premature coronary heart disease
 Cardiovascular and total mortality
 Adverse outcomes after angioplasty
 Carotid artery stenosis
 Stroke, recurrent stroke, silent brain infarct
 Venous thromboembolic disease (PE/DVT)
What factors can cause ↑ homocysteine levels?
Is Knowledge of Homocysteine Level
Useful in Improving Outcome?

There is evidence that reducing homocysteine
levels is of no benefit

There is no evidence to support screening

Routine homocysteine testing is not justified
So… Would you Test Bill?
No.
What would you tell Bill?
Knowing Bill’s homocysteine level will not alter his
management or risk
Modification of risk factors such as DM, smoking,
hypertension, and hypercholesterolemia shown to
be beneficial
Case 3

John, 73y, 1mth history increasing SOB

NSTEMI 18 mth ago

Mild hypertension, hypercholesterolaemia

On Examination
•
•
•
•
Temp 37.6, P 88 reg, BP 150/95
HS dual and nil
Chest dull at bases, some coarse creps
Trace pedal oedema
What else do you want to know?
What are the differential diagnoses?
What investigations would you do?
BNP (Brain Natriuretic Peptide)

Secreted in response to ventricular distension

High negative predictive value useful for ruling out HF
Diagnosing HF is difficult in Primary Care:
- Early symptoms often mild and non-specific
- Clinical findings neither specific nor sensitive
- Echo not readily available
Back to John…

BNP = 52 pmol/L
< 30
30 – 80
>80
What does this mean?
Low – HF unlikely (2%)
Indeterminate – HF still possible
High – HF likely (95%)

A normal BNP in an untreated patient effectively rules-out
heart failure

An intermediate BNP does not rule out heart failure

A high BNP indicates heart failure but does not exclude
other chest/heart problems
Alternative Scenario
What if John’s BNP was 217 pmol/L? (High)
What would this mean?
How would you manage him?
Can you use BNP testing to guide optimal drug
treatment of John’s HF?
When is BNP Useful in General Practice?

High BNP supports diagnosis of HF
o
but does not exclude other conditions

Low BNP can rule out HF in an untreated patient

May have role in known HF patients
o
for helping diagnose cause of acute dyspnoea
When is BNP not Useful in
General Practice?
No role in



screening for asymptomatic LV dysfunction
monitoring well patients who have HF
excluding CHF in those already on therapy
Not recommended for


guiding drug titration in HF
patients with obvious clinical diagnosis of HF
BNP Data
GP count by number of BNP tests
Number of GPs
(9 month period from July 09 – Mar 10)
200
180
175
Total number tests = 4563
Number unique patients = 3728
160
140
120
100
85
80
57
60
40
22
20
20
16
9
4
7
36 to 40
41 to 45
3
8
2
0
1 to 5
6 to 10
11 to 15
16 to 20
21 to 25
26 to 30
31 to 35
46 to 50 51 to 100
> 100
Number of tests/GP
Summary - Diagnostic Dilemmas

‘Off-schedule’ tests were developed in 2° care
-
Place in 1° care not yet established

Only test if it will influence management

Most of these tests have significant limitations

Test results may be misleading

Paramount to use clinical judgment
Take Home Messages

Faecal Calprotectin
•
•

HLA DQ2/DQ8
•
•

second line test
may help rule out Inflammatory Bowel Disease in
young patient with chronic diarrhoea
Not recommended to diagnose Coeliac Disease
30% of Caucasians express these markers
Vitamin D
•
Don’t test, just treat
Take Home Messages Cont’d

Homocysteine
•
•

BNP
•
•
•

Reducing levels does not improve patient outcomes
No role for testing
If normal, useful to rule out HF
If high, may support diagnosis of HF
May be raised by other conditions that strain the heart
Sometimes it is best not to do a test!