Normal values for any laboratory test is the range of lower and upper limits. Below and above it, the test is abnormal and indicates illness (deficiency or excess). These values show that 95% persons will not show abnormal symptoms within this range. Again these values are for detecting illness or they will show that particular nutrient will cause deficiency symptom below that level or will cause toxic symptoms above that level. But these values do not indicate optimum health (As defined by W.H.O.). Person may be having normal values but he may be far away from optimum health.
Example : Normal range of Vit. B12 is 200-900 Pg/ml. But desirable (Optimal) range is above 500 Pg/ml. In many countries normal value for Vit. B12 has been changed to 500-900 Pg./ml. (In Japan). nother example is S.homocystiene. Normal range for homocystiene is 5-15 u mol. But optimal range is 4-7. Homocystiene is better indicator for Vit. B12 deficiency. A number of metabolic function starts when B12 level is above 500 Pg/ml. But compensatory mechanism starts and we don’t get symptom upto 200 Pg/ml or below for a long time. But this level does not indicate optimal health.
We should be cautious when B12 levels are below 500 pg/ml. But if our value is in between 200-500 then existing range show that we are healthy. We may not get magaloblastic Anaemia or neuropathy even below 200 pg/ml for a long time. But we definitely may start getting borderline deficiency symptoms of vilamin B12 just below 500 pg/ml.We should have B12 level in higher range for optimal health.We should find out optimal value of every nutrient and other lab test as a better indicator of health as defined by world health organization(W.H.O.).