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Discuss the laboratory diagnosis of folate deficiency
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Essay of 2 pages for the course laboratory investigation of disease at LJMU (essay prep for exam)
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Discuss the laboratory diagnosis of folate deficiencyA deficiency of folate is caused by various different factors i.e. dietary insufficiency,
malabsorption and an increased nutritional requirement (during pregnancy). Folate has a
variety of functions within the human body. It plays a large role in the methylation of
homocysteine to methionine and is involved in the synthesis of thymidine. Women who are
pregnant have a greater nutritional requirement for folate and is important for them to meet
this to prevent the foetus from developing major congenital deformities of the brain/spine and
helps to develop the neural tubes. Folate works with vitamin B12 in controlling the blood
levels of homocysteine as well as being involved in the synthesis of red blood cells.
Symptoms of folate deficiency include fatigue, shortness of breath, headaches, pallor,
palpitations and weight loss. The first stage of laboratory diagnosis is the assessment of a
full blood count and blood film. If the patient has folate deficiency macrocytic oval red cells
will be visible with a reduced red cell count. Hypersegmented neutrophils should also be
observed on the blood film. If the deficiency is severe, a moderate reduction in the leukocyte
and platelet count may be present.
Macrocytosis refers to a blood condition in which the blood cells are larger than normal and
is reported in terms of mean corpuscular volume (MCV). Patients with folate deficiency tend
to show an increase in MCV with a decrease in haemoglobin. A normal MCV value should
be between 80 and 100 fl. The identification of macrocytosis is achieved through the review
of peripheral blood smears and automated red blood cell indices. The blood smear is more
sensitive for the identification of early macrocytic changes as the MCV represents the mean
of the distribution curve and is insensitive to the small numbers of macrocytes.
Determination of MCV by automation is rarely inaccurate however, hyperglycaemia, marked
leucocytosis and cold agglutinins may result in false elevations of the result. Leaving a blood
sample at room temperature for several hours may also result in false elevations.
The measurement of serum folate is performed to assess the concentration of folate in the
serum. Most clinical laboratories perform serum folate tests by competitive folate binding
protein assays using chemiluminescence or fluorescence detection systems. Normal serum
folate levels should be between 3 and 20 µg/L, patients who are folate deficient will have a
measurement lower than 3 µg/L. Serum folate measurements can be calculated through
automation and the assays used are now widely available and determination rates are much
faster. Fewer analytical variables occur from the use of this test. The value achieved from
serum folate tests are more prone to variation from the patient themselves i.e. through their
diet, alcohol and trauma. Alcohol causes a short-term reduction in the serum folate
therefore, assessment of the red cell folate will give an indication as to how long the folate
levels have been reduced for. In addition, a slight degree of haemolysis will cause a falsely
elevated serum folate level.
The red blood cell folate test measures the concentration of folate stores within the red cells.
Red cells store 95% of the circulating folate. A red cell folate level blow 150 µg/L has been
regarded as sufficient with clinical deficiency. The reference range for this test is 200-800
µg/L. This test is preferred, in some institutions, over serum folate assessment as it is a
better indicator of the long-term folate status. The red cell folate is a reflection of the folate
concentration over the previous 120 days. Patients who have had a blood transfusion in the
last three months will not have an accurate red cell folate level so serum folate
measurements is a good parameter here. The same assay used to perform serum folate
measurements is used for red cell folate but requires a complex preparation. The sample
must be pre-treated to lyse the red cells. This process introduces variables into the testing.
The type and dilution factor of the lysing agent as well as the duration of the lysing step vary
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