Summarised by: Dr Liesel van der Merwe BVSc MMedVet (Med)
Comparison of Serum Spec fPL™ and a New Serum Lipase (DGGR) Assay in 60 Cats Using Pancreatic Histopathology as the Gold Standard Comparison of serum Spec fPL ™ and 1,2-o-dilauryl-rac-glycero-3-glutaric acid –(6’-methylresorufin)-ester assay in 60 cats using standardised assessment of pancreatic histology. S Opplinger et al Journal of Veterinary Internal Medicine, 201(30):764 -770
Why they did it:
The Spec fPL™ is a useful test in diagnosing pancreatitis. Recently a catalytic assay for determining serum lipase activity using 1,2-o-dilauryl-rac-glycero-3-glutaric acid –(6’-methylresorufin)-ester (DGGR …in short!) was validated for use in feline serum. The DGGR lipase test has good agreement with the Spec fPL™ test and is more cost effective.
The two tests have not been compared to a gold standard for the diagnosis of feline pancreatitis.
The problem is that there is not clear cut gold standard to diagnose pancreatitis. Histological findings of pancreatitis in cats appear to be very common. Reports of clinically relevant pancreatitis in cats are however, rare. Added to this is the fact that ante-mortem diagnosis of pancreatitis in cats is difficult because of vague clinical signs, and non-specific clinic-pathologic findings. The sensitivity and specificity of ultrasound is also highly variable. There is also a poor agreement between pancreatic lipase and “typical” ultrasonographic findings of pancreatitis in cats.
What they did:
A total of 60 cats which were euthanased for a variety of reasons were included. Serum was collected a maximum of 12 hours prior to euthanasia and pancreas were collected and sampled within 3 hours of euthanasia.
Serum lipase (DDGR) and Spec fPL™ were measured on the same serum sample. Normal Spec fPL™ was defined as ≤3.5 mg/L, grey zone elevations from 3.6 -5.4 mg/L and elevated ≥ 5.4 mg/L. The normal range for serum lipase (DDGR ) is 8 – 26 U/L.
Serial transverse sections 0.5 cm across were made of the entire pancreas. All tissue sections were evaluated for the presence of neutrophilic inflammation, lymphocytic inflammation, pancreatic oedema, pancreatic necrosis, peri-pancreatic fat necrosis, fibrosis, Cystic degeneration, atrophy, nodular hyperplasia, islet cell amyloidosis and neoplasia. The severity of lesions was scored Grade 1 = <25% tissue affected, Grade 2 = 25 – 50% tissue affected and grade 3 = > 50% tissue affected. Because mild lymphocytic inflammation is shown to be a common finding in feline pancreas additional analyses were performed with 0-10% lymphocytic inflammation defined as no inflammation and 10 -25 % lymphocytic inflammation as grade 1. The mean cumulative score (MCS) was calculated as sum of the score of all sections /number of sections. The disease activity index (AI) was calculated as the sum of the MCS’s of neutrophilic inflammation, lymphocytic inflammation, oedema, necrosis and fat necrosis divide by 5. Disease activity Index classified as <0 implied no histological inflammation and >0 implied evidence of histological inflammation. Cohens kappa (k) coefficient was used to measure agreement between the Spec fPL and lipase DDGR assay as well as between both lipase assays and histology.
What they found:
Spec fPL™was ≤ 3.5/L mg in 50% of cats, between 3.6-5.3mg/L in 40% of cats and ≥ 5.4mg/L in 10% of cats.
Serum Lipase (DGGR) was ≤ 26U/L in 65% of cats and ≥ 27 U/L in 35% of cats.
Histologically nodular hyperplasia was most common– found in 95% of cats, followed by lymphocytic inflammation in 93%, cystic degeneration in 72%, fibrosis in 62%, amyloidosis in 43%, atrophy in 27%, neutrophilic inflammation in 18%, oedema in 15%, peri-pancreatic fat necrosis in 15% and neoplasia in 16% (lymphoma, adenocarcinoma and mastocytoma).
The mean disease activity index (AI) was 0.19 – which is mild. The AI was 0 in 5% of the cats, >0 but < 1 in 92% and >1 in 3% of the cats. When up to 10 % lymphocytic inflammation was considered normal in cats the AI changed to 0 in 70% of the cats, >0 but <1 in 28% and >1 in 2% of the cats.
When no lymphocytic inflammation was considerate normal, agreement between the disease activity index and the assays was:
- spec fPL™ (cut-off > 3.5 mg/L) was slight (k=0.1)
- spec fPL™ (cut-off ≥ 5.4 mg/L) was slight (k=0.07)
- lipase DDGR assay > 26U/L was slight (k=0.06)
The sensitivity and specificity were calculated as:
- sensitivity of Spec fPL™ > 3.5 mg/L = 52.6%
- specificity of Spec fPL™ > 3.5 mg/L = 100%
- sensitivity of Spec fPL™ ≥ 5.4 mg/L = 42.1%
- specificity of Spec fPL™ ≥ 5.4 mg/L = 100%
- sensitivity of DGGR assay = 36.8%
- specificity of DGGR assay = 100%
When up to 10% lymphocytic inflammation was considerate normal, agreement between the disease activity index and the assays was:
- spec fPL™ (cutoff > 3.5 mg/L) was slight (k=0.13),
- spec fPL™ (cutoff ≥ 5.4 mg/L) was fair (k=0.28),
- lipase DDGR assay > 26U/L was moderate (k=0.43)
Sensitivity and specificities where up to 10% lymphocytic inflammation was considered normal were:
- sensitivity of Spec fPL™ > 3.5 mg/L = 61.1%
- specificity of Spec fPL™ > 3.5 mg/L = 54.8%
- sensitivity of Spec fPL ™> 5.4 mg/L = 61.1%
- specificity of Spec fPL ™> 5.4 mg/L = 69%
- sensitivity of DGGR assay = 66.7%
- specificity of DGGR assay = 78.6%
The Receiver Operating Curve (ROC) analysis showed an area under the curve (AUC) of 0.60 for Spec fPL™(95% CI) and an AUC of 0.71 (CI 95%) for the DGGR assay
Take home message
Both lipase assays had a similar performance when compared to pancreatic histology. The agreement of
both lipase assays with histology was limited. There is no further information provided, into what is actually the gold standard for diagnosis of pancreatitis. In this study the prevalence of pancreatitis was 95%, which is higher than a previous study – but this study included multiple transverse sections all of which were examined. This high prevalence in animals without clinical signs or history of GI disease has resulted in debate on the value of histology as a gold standard.
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