This is why Mean Cell Volume (MCV) can never be relied on to rule out B12 Deficiency. #meded
#haematology

1983 Organic psychosis without anaemia or spinal cord symptoms in patients with vitamin B12 deficiency.
("They emphasise that psychiatric manifestations may be the first symptoms of vitamin B12 deficiency and thus antedate anaemia and spinal cord disease.")
http://www.ncbi.nlm.nih.gov/pubmed/6849439

1985 Masked vitamin B12 and folate deficiency in the elderly.
("There is a case for routine screening of the elderly for vitamin B12 and folate deficiency irrespective of the MCV.")
http://www.ncbi.nlm.nih.gov/m/pubmed/3870687/?i=6&from=/9292759/related

1988 Neuropsychiatric disorders caused by cobalamin deficiency in the absence of anaemia or macrocytosis.
("Among 141 consecutive patients with neuro-psychiatric abnormalities due to cobalamin deficiency, we found that 40 (28 percent) had no anemia or macrocytosis")
http://www.ncbi.nlm.nih.gov/pubmed/3374544

1991. Neurologic aspects of cobalamin deficiency.
(".........and in 31 (23.0%), the mean corpuscular volume was normal.")
http://www.ncbi.nlm.nih.gov/pubmed/1648656

1994. Sensitivity of serum methylmalonic acid and total homocysteine determinations for diagnosing cobalamin and folate deficiencies.
("Most of the cobalamin-deficient patients had underlying pernicious anaemia........ Hematocrits were normal in 28% and mean cell volumes in 17%.")
http://www.ncbi.nlm.nih.gov/pubmed/8154512

1995. Neurological complications of acquired cobalamin deficiency: clinical aspects.
("Pharmacological doses of folic acid reverse the haematological abnormalities (eg a MCV) of Cbl deficiency. This may allow neuropathy to develop or progress and make recognition of deficiency more difficult. ")
http://www.ncbi.nlm.nih.gov/pubmed/8534966?dopt=Abstract

1997 Prevalence and haemopoietic effects of low serum vitamin B12 levels in geriatric medical patients.
("..... only thirteen (23%) of the fifty-six patients with a low vitamin B12 had an MCV > or = 100 fl.")
http://www.ncbi.nlm.nih.gov/m/pubmed/9292759/?i=8&from=raised%20mcv%20AND%20B12

2003 Gastric atrophy, metaplasia, and dysplasia: a clinical perspective.
("Patients may have advanced neuropsychiatric manifestations of cobalamin deficiency and yet not be anaemic, have a normal blood smear, and even have serum cobalamin levels in the normal range.")
http://www.ncbi.nlm.nih.gov/m/pubmed/12702963/

2012. M.C.V. should not be the only criteria to order vitamin B12 for anaemia under evaluation
("There is no correlation between vitamin B12 levels and MCV in majority of the cases.)
http://www.scirp.org/journal/PaperInformation.aspx?paperID=25072#.UvLJjH8gGSM

2012 Vitamin B12 deficiency in India: mean corpuscular volume is an unreliable screening parameter.
(In a cohort of 94 patients with low Serum B12, only 26 patients (27%) had raised MCV)
http://www.ncbi.nlm.nih.gov/pubmed/23998863

2012. Misdiagnosed vitamin B12 deficiency a challenge to be confronted by use of modern screening markers
(...."but its absence does not rule out B12 deficiency and it is not a specific marker as using it solely would miss 84 percent cases. Its normal range is 80-96 fl.20 MCV can be within normal range despite B12 deficiency specially with concomitant iron deficiency,....)
http://www.jpma.org.pk/full_article_text.php?article_id=3808

2013 Low Vitamin B12 Levels among Newly-Arrived Refugees from Bhutan, Iran and Afghanistan: A Multicentre Australian Study
("Macrocytosis (MCV>95 fL) was reported in 4.6% (7/151) of cases who also had Vitamin B12<150 pmol/L, and 0.9% (7/762) of cases with Vitamin B12 levels ≥ 150 pmol/L (p=0.004), indicating a sensitivity of 4.6% for macrocytosis in detecting Vitamin B12 deficiency")
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3585239/

2013 Cobalamin deficiency: clinical picture and radiological findings.
("Neuropsychiatric symptoms may precede hematologic signs")
http://www.ncbi.nlm.nih.gov/pubmed/24248213

2014 The neurology of folic acid deficiency.
("In both deficiency states [b12/folate] there is often dissociation between the neuropsychiatric and the hematologic complications.")
http://www.ncbi.nlm.nih.gov/pubmed/24365361

This document showed MCV cut-off used to be lower years ago. (Germany)
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1073874/pdf/jnnpsyc00015-0104a.pdf

2013. Stabler et al
Documents a case with normal MCV & discusses Diagnosis & Treatment of B12 Deficiency
http://www.aahs.org/medstaff/wp-content/uploads/vitbdefnejm2013.pdf

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