PubMed · 13463546
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D G NUTT, T BAKER. 1957. A routine method for red cell diameter measurement.. https://pubmed.ncbi.nlm.nih.gov/13463546/
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Iran is a country with high prevalence of about 5-10% of beta-thalassemia trait. The prevalence of Cooly's anemia has declined from 11.6 in 10000 population to 7.2 in 10000 in a five-year period due to screening program of beta-thalassemia trait before marriage. This study was conducted to compare the sensitivity of mean corpuscular hemoglobin (MCH) < 27 pg and mean corpuscular volume (MCV) < 80 fl as a screening test in first step of screening of beta-thalassemia trait. From 2449 couples (4898 cases) participating in the premarital screening to our clinic, 902 cases with either MCH < 27 pg, MCV < 80 fl, anemia, pallor or family history of beta-thalassemia were enrolled in the study. MCV, MCH as well as Hb A2 were measured in all cases. MCH and MCV had sensitivities of 98.5% and 97.6% for the diagnosis of beta-thalassemia trait, respectively. A false negative value of MCH is about 1% lower than that of MCV. MCH is a more sensitive screening test for detecting beta-thalassemia minor before marriage.
In clinical practice, the finding of an elevated mean corpuscular volume (MCV), macrocytic anaemia or specific neurological symptoms is often the reason to test for vitamin B12 (B12) deficiency. Use of the MCV as a test for the detection or exclusion of B12 deficiency is only justified if the diagnostic accuracy is sufficiently high. However, the sensitivity and specificity are not well known. We performed a systematic review of the diagnostic value of an elevated MCV for B12 deficiency in both anaemic and non-anaemic patients. Of approximately 3500 titles and/or abstracts that were screened, 37 original papers contained usable data. The population under study proved to be the characteristic of major influence on the study outcome. Pooling of data from different studies was performed in subsets of the data corresponding to the different populations studied. The cut-off levels of both MCV and serum B12 had a significant influence on the study outcomes. The data, however, were pooled without taking these cut-off levels into account. The pooled estimates should be interpreted with this limitation in mind. The reference standards were (1) a low serum B12 concentration and (2) a B12 deficiency confirmed by low serum B12 combined with additional diagnostic investigations. In the population that was randomly screened for low serum B12, the sensitivity of the MCV for B12 deficiency was 17%, whereas the sensitivity was 30% for B12 deficiency in patients with anaemia. When measurement of serum B12 was ordered to exclude B12 deficiency as part of the patients' treatment, the sensitivity was 30% for low serum B12 concentration, 58% for B12 deficiency and 75% for B12 deficiency in patients with anaemia. In the population with pernicious anaemia, the sensitivity was far from perfect (77%). In the five studies that reported data on the positive predictive value of the MCV for B12 deficiency, this ranged from 0% (0/6) to 55% (11/20). This systematic review shows that a considerable number of B12-deficient patients will remain unnoticed when the MCV is used to rule in patients for further evaluation. Depending on the population studied, up to 84% of cases will than be missed. The MCV can be used to make the diagnosis of B12 deficiency more--or less--probable. An elevated MCV justifies the measurement of serum B12. The MCV should not be used as the only parameter ruling out the diagnosis of B12 deficiency.