GUIDELINES ON MEASUREMENT OF VITAMIN B12 & FOLATE

INTRODUCTION

. Deficiencies of both vitamin B12 and folate can lead to megaloblastic (macrocytic) anaemia; Appropriate treatment requires differential diagnosis of the deficiency. . It is now recognised that low serum B12 and folate levels can be detected many years before the development of megaloblastic anaemia. . Megaloblastic Anaemia is a late manifestation of deficiency! . B12 deficiency causing neuro-psychiatric disorders can occur in the absence of macrocytic anaemia.

INDICATIONS FOR REQUESTING MEASUREMENT OF B12 AND FOLATE

1. Clinical Criteria (a) Gastro-intestinal disease including glossitis, taste disturbances, previous surgery, malabsorption. (b) Neurological disease including peripheral neuropathy, demyelinating disease of spinal cord, visual loss. (c) Psychiatric disorders including dementia, mental impairment, confusion, depression. (d) Malnutrition including growth impairment in children and those on restricted diets (e.g. vegans). (e) Alcohol abuse (f) Auto-immune disease of thyroid, adrenal and parathyroid glands. (g) Family history of pernicious anaemia. (h) Infertility, when anatomical causes have been excluded. (i) Haematological disease known to be associated with deficiency – chronic haemolytic anaemias, myelofibrosis, myelomatosis. (j) Drug therapy eg. Phenytoin and other anticonvulsants, dihydrofolate reductase inhibitors (methotrexate, trimethoprim and pyrimethamine). (k) Inherited metabolic disease.

2. Laboratory Criteria (a) Macrocytosis (b) Unexplained anaemia (c) Cytopenias

B12 measurement should NOT be requested under the following circumstances: (a) Young, tired all the time, chronic fatigue (b) On treatment with B12 (c) Repeat sample with normal previous result within 2 months (d) Pregnant unless macrocytosis . There are a number of conditions that manifest themselves as low serum B12 levels including. (a) Iron deficiency (b) Pregnancy (c) Multiple myeloma (d) Primary folate deficiency (e) Cancer (f) Oral contraceptive pill (g) Anticonvulsants (h) Advancing age (i) Parasitic competition (j) Pancreatic deficiency (k) Partial gastrectomy/ileal damage (l) Vegetarianism

. Disorders associated with elevated serum B12 levels (a) Myeloproliferative diseases (b) Renal failure (c) Liver disease

PERNICIOUS ANAEMIA (PA)

An auto-immune condition associated with chronic gastric atrophy, is the most common cause of vitamin B12 deficiency.

What tests are useful in diagnosis of PA?

(a) Antigastric parietal cell antibodies - present in approximately 85% of cases - however non-specific (found in auto immune type A gastritis, thyroid disease, iron deficiency anaemia, 3 – 10% of healthy population; incidence increases with age). (b) anti-intrinsic factor antibodies present in 50 – 75% of patients with PA. Highly specific if found in combination with gastric parietal cell antibody.

Other tests that may be useful in difficult cases are as follows: (Please consult with local laboratory before requesting these)

(a) Plasma homocysteine : often raised in both vitamin B12 and folate deficiency. (b) Serum gastrin (fasting) : approximately 80% of cases of PA have increased gastrin (> 200ng/L) (c) Schilling test – NO LONGER AVAILABLE FOLATE

. There are potential interdependencies between folate and vitamin B12 e.g. Folate deficiency may cause low vitamin B12 concentrations because of metabolic blocks. . Low serum level may indicate folate deficiency but common in hospitalised patients (negative folate balance) and after recent ethanol ingestion. . Inappropriate treatment of B12 deficiency with folate can cause irreversible nerve degeneration. . Low red blood cell folate values reflect the second stage of negative folate balance and more closely correlate with tissue levels and megaloblastic anaemia.

Low Serum folate can be caused by: (a) Low dietary intake (b) Malabsorption due to gastrointestinal diseases (c) Inadequate utilisation due to folate antagonist therapy (d) Alcohol (e) OCP (f) Pregnancy (g) Cellular proliferation disorders