Macrocytic anemia laboratory findings

Revision as of 16:46, 21 September 2012 by Shankar Kumar (talk | contribs)
Jump to navigation Jump to search

Macrocytic anemia Microchapters

Home

Patient Information

Overview

Historical Perspective

Classification

Pathophysiology

Causes

Differentiating Macrocytic anemia from other Diseases

Epidemiology and Demographics

Risk Factors

Screening

Natural History, Complications and Prognosis

Diagnosis

Diagnostic Study of Choice

History and Symptoms

Physical Examination

Laboratory Findings

Electrocardiogram

X-ray

Echocardiography and Ultrasound

CT

MRI

Other Imaging Findings

Other Diagnostic Studies

Treatment

Medical Therapy

Surgery

Primary Prevention

Secondary Prevention

Cost-Effectiveness of Therapy

Future or Investigational Therapies

Case Studies

Case #1

Macrocytic anemia laboratory findings On the Web

Most recent articles

Most cited articles

Review articles

CME Programs

Powerpoint slides

Images

American Roentgen Ray Society Images of Macrocytic anemia laboratory findings

All Images
X-rays
Echo & Ultrasound
CT Images
MRI

Ongoing Trials at Clinical Trials.gov

US National Guidelines Clearinghouse

NICE Guidance

FDA on Macrocytic anemia laboratory findings

CDC on Macrocytic anemia laboratory findings

Macrocytic anemia laboratory findings in the news

Blogs on Macrocytic anemia laboratory findings

Directions to Hospitals Treating Macrocytic anemia

Risk calculators and risk factors for Macrocytic anemia laboratory findings

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Laboratory Findings

  • Measurement of homocysteine and Methyl malanoic acid can help confirm and differentiate from folate deficiency.
  • Both are elevated in B12 deficiency while only homocysteine is elevate in folate deficiency.
  • If PA is based on low serum level, Anti-IF antibodies are confirmatory but only present in 50%.
  • Anti-parietal cell Abs are more sensitive (90%) but less specific.

Schilling Test

  • Dietary B12 is bound to factors that are cleaved off by acid leaving B12 free to bind to R factors secreted by the saliva and gastric juice.
  • B12 bound to R factor is not absorbed, but instead requires the alkaline pancreatic secretions and proteases in the duodenum to be freed from R factor.
  • Free B12 can then bind to IF where it is transported to the ileum where a specific receptor then takes up the complex. Therefore, normal B12 absorption and action are dependent of 5 things:
    • Dietary intake
    • Acid in the stomach
    • Pancreatic secretions
    • Secretion of IF by Gastric parietal cells
    • An ileum that can absorb the IF-B12 complex
  • The Schilling test is designed to test the different components of this system.
  • First, 1mg IM B12 is given to saturate transcobalmin.
  • Radiolabeled B12 is then given orally.
  • If it can be absorbed, then >9% will be excreted in the urine in 24 hours and the rest is eliminated in the feces undetected.
  • Renal insufficiency causes a falsely low level.
  • It may be spuriously normal in patients without gastrectomy.
  • Since, acid is required to free dietary B12 from binding factors.
  • Radiolabeled b12 is not bound to these factors. Therefore, persons with impaired acid and pepsin production can absorb too little dietary B12, but will absorb free B12 normally.
  • Part two of the Schilling test is administering radiolabeled b12 with OF to see if the problem corrects. This should differentiate PA from those with intestinal malabsorption. Remember, B12 deficiency affects the intestinal mucosal cells and causes malabsorption. Therefore, Part II should only be done 4 weeks after replacement, giving the mucosa time to regenerate in PA.
  • If Part II is abnormal, Part III is basically a repeat of Part I after a course of antibiotics/vermicides.
  • If this is abnormal, an malabsorptive cause is implicated.

Analysis

The Schilling test was performed in the past to determine the nature of the vitamin B12 deficiency, but due to the lack of available radioactive B12, it is now largely a historical artifact. Vitamin BTemplate:Ssub is a necessary prosthetic group to the enzyme methylmalonyl-coenzyme A mutase. BTemplate:Ssub deficiency leads to dysfunction of this enzyme and a buildup of its substrate, methylmalonic acid, the elevated level of which can be detected in the urine and blood. Since the level of methylmalonic acid is not elevated in folic acid deficiency, this test provides a one tool in differentiating the two. However, since the test for elevated methylmalonic acid is not specific enough, the gold standard for the diagnosis of B12 deficiency is a low blood level of B12. Unlike the Shilling test, which often included B12 with intrinsic factor, a low level of blood B12 gives no indication as to the etiology of the low B12, which may result from a number of mechanisms.

Hematological findings

MCV is often >110. Hct can often be as low as 15. Elevated LDH and bilirubin are seen since dyserythopoesis leads to destruction of >90% of RBC precursors. Hypersegmentation of PMNs is quite sensitive (>5% with 5 or more lobes or >1% with 6 lobes). Reticulocyte, WBC and platelets are low to normal. In one series of patients with B12 deficiency, 64% had a MCV greater than 100, and only 29% had anemia. In general the blood film can point towards vitamin deficiency:

Blood chemistries will also show:

  • Increased homocysteine and methylmalonic acid in B12 deficiency
  • Increased homocysteine in folate defiency

References


Template:WikiDoc Sources