Low platelet count at diagnosis may signal kidney problems for patients
Risk of renal failure evident in those with low levels at early disease stage
Lower blood counts of platelets — tiny cell fragments involved in blood clotting — at the time that ANCA-associated vasculitis (AAV) is diagnosed may be a marker of poorer kidney function and a higher risk of kidney failure, according to a retrospective study from China.
Findings suggest that “platelet count may be an accessible prognostic indicator for renal [kidney] outcomes in patients with AAV,” its researchers wrote.
The study, “Low platelet count at diagnosis of anti-neutrophil cytoplasmic antibody-associated vasculitis is correlated with the severity of disease and renal prognosis,” was published in the journal Clinical and Experimental Medicine.
Kidneys were organs most affected by AAV in all of the study’s patients
AAV refers to a group of autoimmune diseases characterized by inflammation and damage to small blood vessels due to the presence of self-reactive antibodies called ANCAs. When blood vessel inflammation affects the kidneys, it can cause glomerulonephritis, a condition in which the kidneys’ glomeruli, or filtering units, become damaged.
Prior studies have suggested a potential role for platelets in AAV, but whether they are associated with specific clinical characteristics and likely patient outcomes (disease prognosis) is debatable.
A team of researchers retrospectively analyzed data covering 187 newly diagnosed AAV patients (96 men and 91 women) followed for a median of 26 months (about two years) at their clinic, the Xiangya Hospital Central South University in Changsha, the capital of Hunan province.
Patients had a median age of 64 at diagnosis and 51.3% were men. Regarding disease types, most patients (95.2%) were positive for antibodies against myeloperoxidase, one of the most common targets of ANCAs.
At diagnosis, 97.9% of these people had kidney involvement, making the kidneys the most commonly affected organ, followed by the lungs (92% of the patients).
Kidney biopsies were performed in 74 patients (39.6%) and classified according to the Berden system, which divides the pattern of kidney damage into focal, crescentic, mixed, and sclerotic. About half of these patients (56%) showed a mixed ANCA-associated glomerulonephritis.
Over follow-up, 133 patients (71.1%) developed kidney failure and 65 (34.8%) died.
A cutoff value of 2,645 billion platelets was found to be optimal in predicting progression to kidney failure. A total of 111 patients (59%) had platelet counts below that value (lower platelet group), and 76 patients (41%) had higher counts (higher platelet group). Platelet counts for 49 patients were above the normal upper limit of 3 billion.
Significantly poorer kidney function seen in those with lower platelet counts
Patients with lower platelet counts, compared with the higher count group, were significantly less likely to have systemic, or whole body, symptoms (45% vs. 68.4%) and neurological symptoms (7.2% vs. 17.1%).
But this lower platelet group had significantly higher rates of kidney involvement (100% vs. 94.7%) and significantly worse kidney function, as shown by a significantly lower glomerular filtration rate (eGFR) and higher blood creatinine levels.
“No statistical significance about platelet count at diagnosis,” however, is evident “in the four distinct pathological forms of AAV patients according to Berden Classification,” the researchers noted.
People with lower platelet counts were significantly more likely to progress to kidney failure (85.6% vs. 50%) and to undergo a kidney transplant (59.5% vs. 32.9%) than those with higher counts.
The lower platelet group also showed significantly lower overall survival rates at one year (78.4% vs. 92.1%) and three years (63.1% vs. 78.9%). As a result, a significantly greater proportion of this patient group died during follow-up (40.5% vs 26.3%).
An analysis determined these poorer survival rates to be due to higher rates of all-cause death and death associated with kidney failure.
“Collectively, our data suggested that the lower platelet level of AAV patients may be closely related to [more severe] renal damage and worse renal outcomes,” the researchers wrote.
Platelet count as strongest predictor of kidney failure
Further analyses considering several demographic, clinical, and laboratory factors showed that low platelet counts were the strongest predictor of kidney failure, being linked to a 67% higher likelihood of such an outcome.
Blood creatinine levels and age also were predictors of kidney failure, but to a lesser extent.
“To the best of our knowledge, this is the first research to explore the [disease] features and outcomes of AAV patients with low and high platelet counts,” the researchers wrote.
These findings highlight that low platelet counts are linked to greater kidney involvement, worse kidney function, and poorer prognoses in newly diagnosed AAV patients.
Researchers suggested this link may be explained by local platelet aggregation or consumption and, therefore, lower counts of free platelets in the blood, with greater AAV activity and worse AAV-related kidney damage.
Due to the retrospective nature of this work, further studies following patients at various centers over time are required to confirm its findings, the scientists noted.
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