IRIS staging for cats

The four stages at a glance

The stage comes from two blood values read together. Creatinine is a waste product healthy kidneys clear; SDMA is a newer marker that often rises earlier and is less thrown off by muscle loss. US units first, metric in the smaller type.

Stage Creatinine mg/dL (µmol/L) SDMA µg/dL Phosphorus target mg/dL (mmol/L)

1 under 1.6 (under 140 µmol/L) under 18 under 4.5 (1.5 mmol/L) Damage is present but blood values are still normal. Found by SDMA, urine protein, or dilute urine.

2 1.6 to 2.8 (140 to 250 µmol/L) 18 to 25 under 4.5 (1.5 mmol/L) Mild, and where most cats are diagnosed. There's a lot of time here.

3 2.9 to 5.0 (251 to 440 µmol/L) 26 to 38 under 5.0 (1.6 mmol/L) Moderate. Where cats start to feel it, and where most of the useful work happens.

4 above 5.0 (above 440 µmol/L) above 38 under 6.0 (1.9 mmol/L) Advanced. The focus moves to how she feels, and comfort is very much treatable.

When the two markers disagree

If her SDMA says stage 3 and her creatinine says stage 2 on more than one check, she's treated as stage 3. Creatinine depends partly on muscle and SDMA much less so, so in an older cat who has lost muscle, SDMA usually gives the truer picture of her kidneys.

The SDMA flag at 14

Labs flag SDMA as high above 14, while stage 2 doesn't begin until 18. Both are right: above 14 is the level IRIS says can be used to diagnose early disease. A cat at 16 with HIGH printed next to it has something to ask about.

Phosphorus has a floor too

IRIS says not below 2.7 mg/dL at any stage. These targets sit inside the normal range on most lab sheets, so ask what number your vet is aiming for in her, not just whether it's in range.

The bands are wide

The trend over several visits tells you far more than which side of a line she landed on. The bloodwork tracker, kidneycats.org/b/bloodwork, is where the trend lives.