Blood Tests Used in the Diagnosis of Ulcerative Colitis
A number of hematologic tests are performed in the initial screening and follow-up for inflammatory bowel disease (IBD). Abnormalities in acute phase reactants and other laboratory tests do not confirm but raise the index of suspicion for the diagnosis of ulcerative colitis. In this section, a number of useful screening tests are discussed in relation to the abnormalities seen in patients with IBD.
Acute-Phase Reactants
C-reactive protein (CRP), an acute-phase protein produced by the liver, was first identified in 1930 as a substance in the serum of patients with pneumonia. Levels of this protein rise rapidly during inflammatory processes in the body and fall rapidly once inflammation is quiescent, making CRP a valuable tool for monitoring disease activity in some diseases. CRP response is strong with some diseases (e.g., Crohn’s disease [CD], rheumatoid arthritis) and not as reliable with other diseases (lupus, dermatomyositis, ulcerative colitis [UC]). In a study of 100 patients with CD and 43 patients with UC, Solem and colleagues concluded that CRP elevation correlated well with disease activity and endoscopic and histologic inflammation in patients with CD but not with radiologic findings. In patients with UC, CRP elevation was associated with clinical disease activity, elevated erythrocyte sedimentation rate (ESR), anemia, hypoalbuminemia, and mucosal inflammation. Elevation in CRP was not associated with histologic inflammation in UC, although the sample size was small and therefore subject to a Type II statistical error.2014 In UC, CRP levels may be elevated, but not to the extent seen in CD, despite active inflammation. Therefore, CRP is not reliable as an indicator of disease activity for patients with UC.2015
Elevation of ESR is another nonspecific indication of inflammation. In the presence of inflammation, high concentration of fibrinogen causes red blood cells to stick together, allowing them to settle more quickly than when inflammation is not present. ESR is reported in millimeters/hour, the speed at which the cells fall. As with CRP, ESR elevations are not as consistent in UC as they are in CD. In addition, levels remain elevated for a prolonged period of time, making this laboratory test less useful in monitoring of acute disease activity or response to therapy.
Serologic Markers
Serologic markers may be useful in identifying
inflammatory bowel disease (IBD) and in differentiating between Crohn’s
disease (CD) and ulcerative colitis (UC). Perinuclear antineutrophil
cytoplasmic antibody (pANCA) is expressed in a high percentage of
patients with UC and in 10% to 30% of patients with CD affecting the
colon (Crohn’s colitis).2699 In
contrast, anti-Saccharomyces cerevisiae antibodies
(ASCA) are associated with CD in that the antibody is expressed in
50% to 70% of patients with CD. First reported by Saxon, et al., in
1990, investigators concluded that the pANCA assay was associated
with 84% sensitivity in a cohort of 25 patients with confirmed diagnosis
of UC.2018 An
additional early trial was conducted, screening sera from 34 patients
with confirmed UC and 30 patients with CD. Rump, et al., used the
pANCA enzyme-linked immunosorbent assay (ELISA) screen developed by
Saxon and colleagues in addition to ELISA for antibodies against antiproteinase-3
and HEp-2 cells for antinuclear and anticytoplasmic antibodies. Sera
from UC patients tested positively for pANCA, while reaction to other
antibodies was either absent or weak, leading authors to conclude
that pANCA may help to differentiate between UC and CD.2019 Following
these landmark studies, testing for ASCA and pANCA became commercially
available and numerous studies have been conducted to determine the
reliability of these tests for initial diagnosis and differentiation
between subtypes of IBD. A 1996 meta-analysis conducted by Reese and
colleagues included 3,841 UC and 4,019 CD patients from 60 studies
and used meta-regression to determine the effect of age, colonic activity,
and assay type. Investigators determined that
Other Blood Tests
Routine hematologic tests may raise the suspicion of inflammatory bowel disease (IBD), but lack the specificity necessary for confirmation. Routine screening of individuals presenting with symptoms suggestive of IBD may reveal abnormalities in some but not all patients eventually diagnosed with either Crohn’s disease or ulcerative colitis.
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White Blood Count: The absolute white blood count may be elevated in both ulcerative colitis and Crohn’s disease. In many patients, the absolute white count is not elevated, but there may be an increased number of immature neutrophils (i.e., a "left shift").
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Platelet Count: Thrombocytosis is an acute-phase reactant in the presence of inflammation. Platelet counts may also be elevated in a number of other disease states and in the presence of bleeding, making this laboratory finding unreliable as a measure of disease activity. In contrast, mean platelet volume, which accounts for platelet size, is decreased in inflammatory bowel disease (IBD), leading 1 group of researchers to conclude utility of examining mean platelet volume as a marker of disease activity in both ulcerative colitis and Crohn’s disease.2021
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Albumin: Serum levels of albumin decrease in patients with active inflammatory bowel disease (IBD). Hypoalbuminemia in IBD can result from protein loss from the gastrointestinal tract, malnutrition, inflammation, or a combination of factors. Although not specific for IBD, hypoalbuminemia may be an important predictor for failure of medical therapy in CD in children.11444 To date, there are no reports regarding hypoalbuminemia and outcomes in ulcerative colitis.
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Red Blood Count, Hemoglobin, and Hematocrit: Indicators of the overall number of red blood cells and their function can be helpful in monitoring disease activity. Anemia is a consistent clinical feature of inflammatory bowel disease (IBD),2023 although it can occur for a variety of reasons. Decreased red blood count, hemoglobin, and hematocrit can be seen with blood loss, and/or nutritional deficiency (e.g., vitamin B12, folate), all of which are risks associated with IBD. Medications commonly used to treat IBD increase the risk of folate deficiency and are associated with bone marrow suppression. Malabsorption associated with Crohn’s disease (CD) predisposes individuals to deficiencies in vitamin B12 and folate. While abnormalities in red blood count in patients with IBD are important, further diagnostic evaluation is needed to identify the cause
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Iron Indices: Iron deficiency anemia is an important and consistent complication of inflammatory bowel disease (IBD). Anemia in IBD patients occurs due to intestinal blood loss.2023 In iron deficiency, serum levels of iron and ferritin are low and total iron binding capacity (TIBC) is high, reflecting efforts to produce more transferrin to bind available iron. In addition to iron deficiency anemia, IBD predisposes individuals to anemia of chronic disease. In the presence of inflammation, anemia of chronic disease occurs through several cytokine-driven mechanisms, including diversion of iron traffic, inhibition of erythroid progenitor proliferation and differentiation, blunted erythropoietin response, and diminished erythrocyte life cycle.2023 While serum iron level is low, ferritin is often normal or high and TIBC is low or normal in individuals with anemia of chronic disease.
Content on this page was last reviewed on October 31, 2009.
Content on this page was last changed on March 19, 2009.
References:| 2014. | Solem CA, Loftus EV, Tremaine WJ, et al. Correlation of C-reactive protein with clinical, endoscopic, histologic, and radiographic activity in inflammatory bowel disease. Inflamm Bowel Dis. 2005;11(8):707-712. |
| 2015. | Vermeire S, Van Assche G, Rutgeerts P. C-reactive protein as a marker for inflammatory bowel disease. Inflamm Bowel Dis. 2004;10(5):661-665. |
| 2018. | Saxon A, Shanahan F, Landers C, Ganz T, Targan S. A distinct subset of antineutrophil cytoplasmic antibodies is associated with inflammatory bowel disease. J Allergy Clin Immunol. 1990;86(2):202-210. |
| 2019. | Rump JA, Schölmerich J, Gross V, et al. A new type of perinuclear anti-neutrophil cytoplasmic antibody (p-ANCA) in active ulcerative colitis but not in Crohn’s disease. Immunobiology. 1990;181(4-5):406-413. |
| 2020. | Reese GE, Constantinides VA, Simillis C, et al. Diagnostic precision of anti-Saccharomyces cerevisiae antibodies and perinuclear antineutrophil cytoplasmic antibodies in inflammatory bowel disease. Am J Gastroenterol. 2006;101(10):2410-2422. |
| 2021. | Kapsoritakis AN, Koukourakis MI, Sfiridaki A, et al. Mean platelet volume: a useful marker of inflammatory bowel disease activity. Am J Gastroenterol. 2001;96(3):776-781. |
| 2023. | Gasche C, Lomer MC, Cavill I, Weiss G. Iron, anaemia, and inflammatory bowel diseases. Gut. 2004;53(8):1190-1197. |
| 2699. | Batres LA, Baldassano RN. Evaluation of the patient suspected of having inflammatory bowel disease. In: Lichtenstein G, ed. The Clinician’s Guide to Inflammatory Bowel Disease. Thorofare, NJ: Slack Inc.; 2003:315-323. |
| 11444. | Gupta N, Cohen SA, Bostrom AG, et al. Risk factors for initial surgery in pediatric patients with Crohn’s disease. Gastroenterology . 2006;130(4):1069-1077. |
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