CH, CHCM and cHGB (hemoglobin measured inside red cells) in cats and dogs

What it shows

The usual hemoglobin is measured chemically: the red cells are burst, and the freed hemoglobin is read by its colour. MCH and MCHC are then calculated from that number. Laser-based analyzers, such as the ADVIA, can also pass intact red cells one by one through a laser beam: light scattered forward shows the size of the cell, light scattered to the side shows how much hemoglobin it holds.

From this the analyzer reports three values:

• CH (cellular hemoglobin content) — the average amount of hemoglobin per cell, the optical counterpart of MCH. Like MCH it is content, not concentration, so it also follows cell size.
• CHCM (cellular hemoglobin concentration mean) — the average concentration of hemoglobin inside cells, the optical counterpart of MCHC.
• cHGB (calculated hemoglobin) — computed from CHCM and the red cell volume and count; it reflects hemoglobin in intact cells only.

Impedance analyzers cannot measure these values at all.

Higher than reference — what it may be a sign of

• Shrunken red cells in the sample — too much EDTA in an underfilled tube, or low sodium, raise CH and CHCM together with MCH and MCHC, while MCV falls.
• Larger cells — CH, like MCH, goes up and down with cell volume.
• A gap between the pairs — when MCHC is high but CHCM is not, the chemical measurement was likely distorted: lipemia does not affect CHCM, Heinz bodies (clumps of damaged hemoglobin inside red cells) affect it less than MCHC, and with clumped red cells CHCM is the more accurate value.

Lower than reference

• Too little hemoglobin in the cells — a red cell with less hemoglobin scatters less light to the side, as iron-deficient cells do.
• Swollen red cells — after long storage, or when the blood is very concentrated (high sodium or glucose), CH and CHCM fall together with MCH and MCHC, while MCV rises.
• Hemolysis in the tube — burst cells cannot be measured optically, so cHGB, CH and CHCM drop, while the chemically measured hemoglobin does not.

Look at together with

• Hemoglobin against cHGB — a large gap between them is itself a sign of a sample effect.
• MCH against CH and MCHC against CHCM — when the two halves of a pair agree, the chemical values can be trusted.
• MCV — tells whether a change in CH is about cell size.
• Reticulocytes — some analyzers report the same values for young cells only, such as reticulocyte hemoglobin (CHr), which in people falls earlier than CH or MCH when iron runs short.
• Iron panel — if small, poorly filled cells suggest iron deficiency.

Units and conversion

CH is reported in picograms (pg; пг on Russian-language forms), as MCH is; the factor is 1. CHCM and cHGB are reported in g/L or in g/dL: 1 g/dL equals 10 g/L, so 33 g/dL is 330 g/L. In the app each row keeps the unit printed on the form, and the chart converts to one unit so forms from different labs line up.

Reference range

The reference range is on your lab’s form. These values come from one type of analyzer, so their ranges belong to that analyzer. The Cornell laboratory behind eClinPath reports the usual MCH, MCHC and measured hemoglobin, and uses CH, CHCM and calculated hemoglobin instead only when the measured hemoglobin is considered inaccurate, for example with lipemia or hemolysis. So if these lines appear on a form, it may mean the lab judged the usual values unreliable for this sample. The vet reads each pair side by side and looks at the trend rather than a single value.

Cats and dogs

Sources

1. eClinPath (Cornell University) — Laser-based hemoglobin analysis
2. eClinPath (Cornell University) — MCH/CH
3. eClinPath (Cornell University) — MCHC/CHCM
4. eClinPath (Cornell University) — Hemoglobin
5. eClinPath (Cornell University) — Reticulocyte indices
6. eClinPath (Cornell University) — RBC inclusions (Heinz bodies)