Clinical utility of urinary liver-type fatty acid binding protein measured by latex-enhanced turbidimetric immunoassay in chronic kidney disease.

BACKGROUND: Urinary liver-type fatty acid binding protein (L-FABP) measured by enzyme-linked immunosorbent assay method (ELISA) was approved as a clinical biomarker of tubular damage by the Japanese Ministry of Health, Labor and Welfare (MHLW) in 2011. We evaluated a new latex-enhanced immunoturbidimetric assay (LTIA) to evaluate the clinical utility of urinary L-FABP measured by LTIA versus an ELISA assay. METHODS: LTIA with anti-human L-FABP mouse monoclonal antibodies was performed using an automated clinical chemistry analyzer. Five positive samples with low, medium and high L-FABP concentrations were analyzed to determine the within-run precision. In patients with chronic kidney disease (CKD) (n=91), urinary L-FABP levels were measured by ELISA and LTIA. RESULTS: Measurement of urinary L-FABP revealed urinary L-FABP levels within 30 min. The within-run coefficient of variation was 10.0% for 1.4 ng/mL, 4.4% for 2.5 ng/mL, 3.2% for 9.8 ng/mL, 1.5% for 50.1 ng/mL, and 1.2% for 102.7 ng/mL. Concentrations of urinary L-FABP measured by LTIA were significantly correlated with those measured by ELISA (ρ=0.932). Proportional systematic error was almost within limits of agreement (LOA). Urinary L-FABP levels measured by LTIA were significantly correlated with urinary albumin (ρ=0.634), urinary NAG (ρ=0.688) and eGFR (ρ=-0.561). CONCLUSIONS: Measurement of urinary L-FABP by LITA was simple, speedy, and similar in quality to ELISA results. Therefore, this method was approved as external body diagnosing medicines by the Japanese MHLW in 2014. Urinary L-FABP is expected to be widely used in various pathophysiological conditions by measuring urinary L-FABP using LTIA.

Marked hyperkalemia due to inappropriate blood sample storage in two suspected cases of familial pseudohyperkalemia.

We herein report two suspected cases of pseudohyperkalemia who presented with severe hyperkalemia examined at small primary care clinics; however, re-exams at a tertiary care hospital showed normal potassium levels. We reproduced the laboratory examination conditions of the clinics and found that hyperkalemia was due to sampling/storage condition of serum, which is strongly suggestive of familial pseudohyperkalemia (FP). FP is a possible but under-appreciated cause of hyperkalemia, which does not require treatment, so it is important to include FP in the differential diagnosis of hyperkalemia especially in cases with discrepant of serum potassium levels at different settings.