High MCH and High MCHC in Cats – What the Pattern Means

High MCH and High MCHC in Cats – What the Pattern Means

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Two Numbers That Describe One Thing

MCH and MCHC both describe the hemoglobin carried inside a cat’s red blood cells, which is the pigment that gives them their colour and lets them carry oxygen. MCH is the average amount of hemoglobin in a single red cell, while MCHC is how tightly that hemoglobin is packed into the volume of the cells. The detail that explains almost everything about a high reading is that neither value is measured directly. Both are calculated from the analyser’s hemoglobin reading and its red-cell counts, so anything that disturbs the hemoglobin figure flows straight into them. That is why these two indices tend to move together, and why a rise in both is treated as a single pattern rather than two separate findings. For the wider picture of how these indices sit within the rest of the count, the overview of how to work up the feline red-cell line is a useful companion.

It also helps to understand why these calculated values exist at all. Long before automated analysers, clinicians wanted a shorthand for the quality of the red cells rather than just their quantity, a way of saying whether each cell carried a normal load of hemoglobin or looked pale and under-filled. MCH and MCHC fill that role, and at the lower end of their range they still do useful work, flagging cells that are short of hemoglobin. The trouble is specific to the high end. Because the arithmetic that produces them places the hemoglobin reading on top, any error that lifts that reading lifts the indices with it, and there is no biological ceiling in the calculation to stop the number climbing past what a real cell could ever contain. The result is a value that is informative when it falls but suspicious when it rises, and recognising that asymmetry is half the work of reading these two lines correctly.

Why a Cell Cannot Truly Hold More

The reason a high MCHC is taken so cautiously comes down to simple physiology. A mature red cell is already filled with hemoglobin to close to its physical limit; there is little spare room inside for more. So a concentration meaningfully above the reference interval is essentially something the body cannot produce. When an analyser nonetheless reports one, the far more likely explanation is that the hemoglobin reading feeding the calculation was falsely high, rather than that the cells genuinely became super-concentrated. This is the single most important idea to carry away from a high MCHC, and it is why an experienced reader treats the number as a clue to a sample problem rather than a clue to a disease. A high MCH follows the same logic, because it is built from the same hemoglobin reading. The same caution applies in other species too, which is why the canine version of this pattern is interpreted along very similar lines in high MCH and MCHC in dogs, and why an isolated high MCH on its own is rarely treated as alarming, a point explored in whether a high MCH always means trouble.

The Hemoglobin Indices in Context

Reference intervals depend on the analyser and method, so the range printed on your own cat’s report is the final word. As an evidence-based guide, the verified feline intervals for the hemoglobin indices and the directly measured red-cell values that frame them are listed below. The point of showing them together is that a veterinarian rarely reads MCH or MCHC alone; they are interpreted against the values the machine actually measures, especially the hematocrit and the red-cell count. Those measured values, together with the mean cell volume, are the ones that genuinely describe the red-cell line, and they are the same numbers that move first when the red-cell mass is genuinely too high, as discussed in a high hematocrit and red-cell count. The hemoglobin indices are best thought of as a layer of description resting on top of those core measurements: useful when everything fits together, but easily distorted when the sample itself is not in good condition.

See the full reference intervals for the cat — every value cited to the laboratory document or paper it came from.

Hemolysis: The Most Common Culprit

Hemolysis simply means red cells have broken open and released their hemoglobin into the surrounding plasma. The freed hemoglobin does not disappear; the analyser still measures it. So the hemoglobin figure becomes too high for the number of intact cells remaining, and the calculated MCH and MCHC are dragged upward as a result. The crucial nuance is that this rupture can happen for two very different reasons. Sometimes it occurs inside the cat, as a genuine medical event, and sometimes it happens entirely outside the cat, during a difficult blood draw, on handling, or while the sample waits to be run. A struggling or small patient, narrow needles, vigorous mixing, and delays all encourage cells to break in the tube. Because that second category is so common, a high MCHC accompanied by a hemolysis flag on the report is usually read as a sample issue first, and a fresh draw often settles the matter. This is also why these indices are interpreted alongside the broader question of whether the cat is genuinely anemic, since true in-body hemolysis would be expected to show up in the directly measured red-cell values too.

Lipemia and Other Sample Interferences

The second great cause of a falsely high reading is lipemia, the milky or fatty look that plasma takes on when it is loaded with fat. It is often seen simply because a cat was not fasted and the blood was drawn after a meal, though some metabolic conditions can produce it as well. Many analysers read hemoglobin by shining light through the sample, and the cloudiness of lipemic plasma scatters that light, so the machine reports more hemoglobin than is really there. As with hemolysis, that inflated hemoglobin figure flows directly into the calculated indices and lifts both MCH and MCHC. Most laboratories grade the appearance of every sample and note lipemia on the report, which gives the veterinarian a ready explanation when it sits beside a high index. Other handling factors, such as samples that have been stored too long or are partly clotted, can disturb the count in their own ways, which is one more reason the indices are never read in isolation from the rest of the complete blood count.

There is a practical side to this that owners can quietly help with. Where a high MCHC has been blamed on lipemia, a veterinarian may suggest fasting the cat before a repeat sample, since blood drawn several hours after the last meal is less likely to be cloudy. Where hemolysis was the issue and the cat is otherwise well, the answer is often simply a calmer, gentler second draw. These are small, low-stakes adjustments rather than treatments, and they reflect the underlying truth that the original reading described the conditions of the sample more than the state of the cat. It is also why a veterinarian will not usually chase a high MCHC with a cascade of further testing on its own; the more proportionate step is to clean up the sample and look again, and to let the directly measured values and the cat’s clinical picture decide whether anything more is warranted.

What the Veterinarian Reads Instead

Because MCH and MCHC are calculated rather than measured, an experienced reader quietly demotes them and leans on the values the analyser truly counted. The packed cell volume, or hematocrit, and the red-cell count tell the honest story of whether a cat has too few, too many, or a normal number of red cells, and whether it is anemic. The mean cell volume describes the size of those cells without depending on the hemoglobin reading in the same way. When a high MCHC appears against an otherwise unremarkable, well-measured count in a healthy-looking cat, the index is set aside as artifact. This same habit of trusting the measured values over the derived ones runs through the broader skill of reading a feline blood panel and of making sense of common abnormalities without overreacting to any one line. If something genuine is going on with the red cells, it tends to declare itself in those measured numbers and in how the cat looks, not in an isolated rise of a calculated index.

When the Same Indices Fall Instead

It is worth being clear that a decrease in these indices points in a completely different direction from an increase, so the two should never be confused. A low MCH is associated with iron-deficiency anemia, where red cells are made with less hemoglobin than they should carry. A low MCHC can appear with regenerative anemia and with iron deficiency, partly because the young red cells released in a regenerative response are larger and relatively less concentrated with hemoglobin. Those low patterns genuinely reflect the cells and are followed up as real findings, often with a look at the causes of feline anemia and at the measured red-cell values. The contrast is the key point: a high reading usually means the sample, while a low reading usually means the cells. Keeping that asymmetry in mind prevents the common mistake of treati