Although initial laboratory testing (a serum chemistry profile, complete blood count [CBC], and urinalysis) is essential to
diagnosing kidney disease, these tests cannot, by themselves, differentiate between AKI and CKD. These two disease processes
often have similar initial laboratory findings. But patients with results consistent with renal failure may have additional
findings that support further characterization of the disease process as acute or chronic, such as an elevated parathyroid
hormone (PTH) concentration.
Serum chemistry profile
Calcium concentrations. Hypercalcemia has traditionally been associated with CKD. It can develop in the presence of renal
tertiary hyperparathyroidism, if the hyperplastic parathyroid gland autonomously starts secreting PTH despite normal to high
serum ionized calcium concentrations. This only occurs with CKD. However, because ionized hypercalcemia can cause AKI and
because hypercalcemia can also be secondary to either AKI or CKD, it is not useful in distinguishing between acute and chronic
disease. No cats in one study of 32 cats with AKI were hypercalcemic (Worwag S, Langston CE, Unpublished data, 2009), although
total hypercalcemia was present in 62.5% of dogs with AKI from grape or raisin intoxication and in 30% of dogs with AKI in
another study.34,35 With CKD, 9% to 22% of dogs and cats have total hypercalcemia,17,35-39
whereas 0% to 30% have ionized hypercalcemia.14,35-37,40
Total hypocalcemia occurs in 7% to 23% of dogs with CKD,17,35,41,42
compared with 10% to 15% of dogs with AKI.37-39 In cats with CKD, 8% to 15% have total hypocalcemia, compared with 30% of cats with AKI (Worwag S, Langston CE, Unpublished
data, 2009). Given these similar ranges for both AKI and CKD, total hypocalcemia cannot be used to differentiate acute from
chronic kidney disease.
In the presence of CKD, the total calcium concentration is poorly predictive of ionized calcium, the metabolically active
Thirty to forty percent of dogs and 10% to 26% of cats with CKD have ionized hypocalcemia.35,37,40,41,43 Data on ionized calcium concentrations in AKI are not available.
Unfortunately, because of the prevalence of both hypercalcemia and hypocalcemia with both acute and chronic kidney disease,
the value of calcium concentrations in differentiating between acute and chronic kidney disease is quite low.
Evidence of a nonregenerative anemia on a CBC should trigger suspicion that the azotemia is long-standing. Seventy percent
of dogs with CKD in one study presented with a nonregenerative, normocytic, normochromic anemia,44 compared with 25% of dogs with AKI presenting with anemia in another study.13
Erythropoietin is an important factor in replacing senescent red blood cells, and erythropoietin production decreases in the
face of CKD. A relative or absolute erythropoietin deficiency leads to chronic, nonregenerative anemia. With severe AKI, erythropoietin
production may be decreased, but anemia would not be expected to occur unless there is accelerated red blood cell loss (bleeding
Conditions that contribute to anemia include low-grade hemolysis secondary to uremic toxin accumulation causing increased
erythrocyte fragility; blood loss associated with platelet dysfunction, especially from gastrointestinal ulcers; and increased
PTH concentrations inhibiting hematopoiesis.44 Patients with renal disease may have less severe clinical signs from anemia compared with patients with anemia associated
with other disease processes, since concurrent increases in serum phosphate concentrations and erythrocyte 2,3-diphosphoglycerate
concentrations may improve tissue oxygenation in the face of a lower hematocrit.44