Megaloblastic Anaemia Flashcards
What are the follow up tests are needed to diagnose megaloblastic anaemia after seeing macrocytosis and hypersegmentation?
Homocysteine:
- homocysteine (Hcy) is elevated in B12 and folate deficiencies, but it further increases with age of the sample.
- serum or plasma is treated with a reducing agent that converts all Hcy species into the reduced form (tHcy) which is measure either directly or after derivatisation.
- HPLC or amino acid analyser and an ion exchange column is used to separate the derivatised Hcy molecules based on retention times.
- the quantification is achieved by comparing the Hcy peak area with the peak area of a Hcy standard that is elated at the same retention time.
Methylmalonyl CoA (MMA):
- B12 deficiency leads to increased MMA. Doesn’t occur in folate deficiency, hence this is the differentiator!
- Excreted in urine so must be careful in renal patients
- > 90% specificity and sensitivity
- MMA is measured by selected ion monitoring isotope dilution GCMS in a random spot urine specimen
- result is normalised to urine creatinine levels to correct for urine dilution
- the urinary creatinine/MMA ratio test (uMMA) more accurate than the blood test
What are the changes to FBC morphology?
In folate and B12 deficiency thymidine synthase production is impaired and DNA synthesis is interrupted.
When deficient in either of these we are not complete in DNA synthesis in the S phase to produce the correct amount of DNA thymidine. This give asynchronous cell division, where the nucleus cant mature (without the correct amount of DNA) but the cytoplasm does. So we get the correct amount of mitochondria, ribosome, etc, this is why we get enlarged cells.
These cells then undergo intramedullary apoptosis in the bone marrow. The bm then compensates by trying to produce new RBCs, but without the effective DNA it can only form lots of reticulocyte precursors (progenitor cells), but development stops at this point, making the bone marrow hyperplasic. Since the cells never mature to reticulocytes we don’t actually see an increased concentration of retics (normal count).
Nuclear maturation is slowed whereas cytoplasmic maturation is unimpeded. This leads to asynchronous maturation.
This can lead to hypersegmented polymorphonuclear neutrophils as well (should have 3-5 segments usually but in B12 and folate deficiency we see 7+).
OVERALL WE SEE A LOW RETICULOCYTE COUNT, INTRAMEDULLARY HAEMOLYSIS LEADING TO INCREASED LDH AND BILIRUBIN
(As red cells apoptose we see more bilirubin (transfers to liver, causing slight jaundice) and LDH, both are breakdown products)
