Outdated medical references say or imply that absence of anemia or a normal B12 test rule out deficiency. They do not.
Many years ago it was discovered and accepted that a substantial percentage of people being damaged by B12 deficiency do not become anemic. Apparently it is even more common for people incurring primarily neurological damage not to become anemic, and in some cases the patient still does not become anemic even though severe damage has already occurred and is worsening. Some individuals are near death due to untreated B12 deficiency and are not anemic.
Decades ago, the B12 test was shown unreliable. It is common for people who are B12 deficient to test within the "normal" range. And although less common, some test a lot higher. The danger is in having too little B12: some of the better "normal" ranges do not have an upper number.
Goldman: Cecil medical textbook
"Serum cobalamin and folate levels therefore cannot be used alone to establish the diagnosis of cobalamin or folate deficiency unequivocally. The problem is compounded by the fact that not all patients with clinically confirmed cobalamin or folate deficiency (defined as those who have objective clinical responses to appropriate therapy) have low values for serum cobalamin or folate. The following distribution of serum cobalamin levels has been noted in clinically confirmed cobalamin-deficient patients: less than 100 pg/mL, approximately 50%; 100 to 200 pg/mL, approximately 40%; 200 to 350 pg/mL, approximately 10%; and higher than 350 pg/mL, approximately 0.1% to 1%."
There is a better cobalamin serum test (B12 test) now, but you almost certainly will not be given that type, and even then it is not wise to rely on that test to rule out deficiency when there are symptoms (which can vary so much from individual to individual that virtually any symptom should be suspect).
Metabolites: Homocysteine and Methylmalonic Acid
These tests should be given anyone who has symptoms OR a B12 serum less than 350 pg/mL. It is important to recognize that if B12 has been taken, homocysteine and/or methylmalonic acid that may have been high can normalize quickly and stay normal for a long time in spite of deficiency.
Also, it is important to remain clear that neither will be elevated in a small percentage of people who are deficient and have had no treatment.
More physicians have become aware of the homocysteine test in recent years, but still it is used too little. High homocysteine is likely due to deficiency in one or more of the following: B12, folate (folic acid), B6. It is crucial for the patient to know that treating high homocysteine with folic acid without making absolutely sure the patient is getting plenty of B12 is a very dangerous thing. The folic acid is one of those things that can mask hematological signs of B12 deficiency while allowing the damage to continue. It is suprising that some doctors don't know this, because this fact has been a part of much medical literature for decades.
Those whose high homocysteine does not come down to around the middle of the normal range when B12, B6, and folic acid are taken in plentiful quantities (at least 1000 mcg B12, in case severe malabsorption is present) should suspect kidney problems or an inability to use the form of the vitamins used. If using a better form the vitamins (P-5-P B6, methylcobalamin B12, and methylfolate) does not bring homocysteine down to around mid normal, kidney problems are very likely.
High methylmalonic acid occurs in many people being damaged by B12 deficiency. If the cause isn't B12 deficiency, it is likely that there is a kidney problem. The methylmalonic acid test is not ordered nearly as frequently as it should be.
The Methylmalonic acid and homocysteine tests cannot rule out B12 deficiency 100%, but taken together they will help a great deal in diagnosing most people with B12 deficiency who have not already begun treatment.
More to come....