The MCHC (mean corpuscular hemoglobin concentration) is the mean hemoglobin concentration in a specific volume of red blood cells (or is the percentage of the red blood cell that contains hemoglobin) and is usually a calculated value by dividing the hemoglobin by the red blood cell mass (HCT or PCV).
MCHC (g/dL) = (Hgb ÷ PCV or HCT) x 100
However, the hematology analyzer at Cornell University provides both a calculated MCHC (from direct measurement of hemoglobin after lysing the red blood cells and measuring the hemoglobin spectrophotometrically) and a directly measured CHCM, which is based on the ability of hemoglobin to scatter laser light sideways (high angle light scatter) as intact red blood cells pass through a laser beam (also called internal complexity). Thus, for every blood sample we run, we obtain a calculated MCHC (from measured hemoglobin after lysing RBC) and a directly measured CHCM (from internal complexity of intact RBC). We usually report the MCHC, but in some cases we provide the CHCM and a hemoglobin calculated from the CHCM. This is particularly used with lipemic samples in which lipemia falsely increases the measured hemoglobin concentration, but has no effect on the HCT or RBC count, resulting in a falsely increased MCHC (and MCH). In these situations, we delete the measured hemoglobin (as it is falsely high) and the related indices dependent on the hemoglobin result, MCH and MCHC, and provide results for a calculated hemoglobin, CH and CHCM, which are all obtained from the light scatter of intact RBC. This is summarized below.
- MCHC (mean corpuscular hemoglobin concentration): This is calculated from a directly measured hemoglobin and is the RBC index that is provided on our routine hemograms for most species (exotics are an exception). Since it is a calculated value, dependent on the hemoglobin and HCT (MCV and RBC count), false increases or decreases in any of these results will falsely change the MCHC.
- CHCM (Cell hemoglobin concentration mean): CHCM is measured from laser light scatter and is used to back-calculate a cellular hemoglobin, which reflects the hemoglobin content within intact red blood cells. It is affected by far fewer artifacts than the measured hemoglobin and we provide this value (with the calculated hemoglobin and CH) when the measured hemoglobin is inaccurate, e.g. lipemia, and other settings where the red blood cell count is proportionally lower than the hemoglobin (in vitro or in vivo hemolysis, agglutination).
|Hemoglobin or Hgb (g/dL)||Direct measurement||RBC are lysed and hemoglobin is measured at a specific wavelength (540 nm)||Routine hemogram, except if lipemia falsely increases. Does not accurately reflect oxygen-carrying capacity with true in vivo intravascular hemolysis but does with in vitro hemolysis|
|MCH (pg)||Calculated from the measured hemoglobin||(Hgb x 10) ÷ RBC||Routine hemogram, unless falsely increased (e.g. lipemia, agglutination, in vivo intravascular or in vitro hemolysis)|
|MCHC (g/dL)||Calculated from the measured hemoglobin||(Hg ÷ HCT or PCV) x 100||see MCH|
|Calculated or cellular hemoglobin||Calculated from the optically measured CHCM||(CHCM x HCT)/1000or (CHCM x RBC x MCV)/1000||Not on routine hemograms, unless measured hemoglobin inaccurate or disproportionate to RBC count (see above)|
|CH (pg)||Direct (= MCH in intact RBC only)||From internal complexity of intact RBC by side scattered (low angle) laser light||Not on routine hemograms, unless MCH inaccurate (see above)|
|CHCM (g/dL)||Direct (= MCHC in intact RBC only)||See CH||Not on routine hemograms, unless MCHC inaccurate (see above)|
Units of measurement
MCHC and CHCM are measured in g/dL (conventional units) or g/L (SI units). The conversion formula is as follows:
g/dL x 10 = g/L
EDTA is the preferred anticoagulant.
The MCHC is unstable. It can either decrease (storage-associated RBC swelling, which increases the MCV) or increase if there is RBC lysis in vitro with storage.
- Lipemia: Will falsely increase MCHC due to false increases in measured hemoglobin. It will have no effect on the CHCM.
- Hemolysis: In vivo intravascular hemolysis or in vitro (artifactual) hemolysis falsely increase the MCHC (measured hemoglobin is proportionally higher than HCT or PCV) and decrease the calculated hemoglobin and thus the CHCM (because there are fewer intact RBC – this will be a false decrease with in vitro but not in vivo intravascular hemolysis).
- Icterus: No effect.
- Heinz bodies (many, particularly if large) may falsely increase the MCHC with less of an effect on the CHCM.
- Agglutination: Falsely increases the MCHC (measured hemoglobin is proportionally higher than HCT) with newer optical-based analyzer. The CHCM is more accurate in this setting.
- Excess EDTA: This dehydrates RBC, falsely increasing the MCHC and CHCM.
Increased values (hyperchromic)
- MCHC: This is always an artifact because RBCs cannot contain more hemoglobin than normal. This is most frequently due to lipemia, but can also be seen with large numbers of (typically large) Heinz bodies, hemolysis (in vitro or in vivo intravascular), RBC nuclei (many nRBC), and agglutination. Other causes of a high MCHC is RBC dehydration if there is excess EDTA for the amount of blood in the sample (EDTA dehydrates RBC) or hypo-osmolality – in the latter cases, the high MCHC can be accompanied by a lower MCV (MCV will be lower than it “should be” even if not below the reference interval).
- CHCM: Excess EDTA or hyponatremia.
Decreased values (hypochromic)
- MCHC/CHCM: RBC swelling with storage and causes of hyperosmolality such as hypernatremia and hyperglycemia (see MCV). This is the most common cause of a low MCHC and is usually seen with an increased MCV (may not always be above the reference interval). The CHCM will also be low in this setting.
- Regenerative anemia: Immature RBC have less hemoglobin than normal. This is not a consistent finding in regenerative anemia. Remember, changes require that most of the RBC have less hemoglobin to shift the mean value below the lower reference limit. Red blood cells do not appear hypochromic on a blood smear (they appear to have normal hemoglobin content visually on blood smear examination.
- Iron deficiency anemia: Multiple causes. RBC may be hypochromic on smear examination (contain less hemoglobin which leads to increased central pallor). Animals with iron deficiency are usually anemic by the time the MCHC is decreased. Thus hypochromasia (low MCHC) in the absence of anemia should not be automatically attributed to iron deficiency. However hypochromic RBCs (cells that contain less hemoglobin than normal) may be evident in a blood smear before the MCHC is decreased (but are usually only seen if the animal is anemic).
- Portosystemic shunts: The low MCHC is attributable to a relative or functional iron deficiency (iron is sequestered in the body versus truly deficient). Most animals with low MCHC from shunts usually are truly iron deficient (from concurrent gastrointestinal bleeding).
- Decreased hemoglobin production: Lead poisoning, vitamin B6 deficiency, copper deficiency. These are very uncommon causes of a low MCHC.
- Pathologic causes of RBC swelling: RBC membrane changes, e.g. hereditary stomatocytosis. Alterations in DNA metabolism do not usually result in low MCHC.