Usefulness of simultaneous determination of alpha-fetoprotein and des-gamma-carboxy prothrombin in hepatocellular carcinoma

Serum gamma-fetoprotein (AFP) and plasma des-gamma-carboxy prothrombin (DCP), a protein induced by vitamin K absence or antagonist II (PIVKA-II) levels, were measured in 197 patients with primary hepatocellular carcinoma (HCC). DCP levels were determined by conventional enzyme immunoassay kit (E-1023) and a newly developed high-sensitivity kit using the avidin-biotin complex method. Cut-off levels of AFP and DCP by the E-1023 kit and of DCP by the high-sensitivity kit were put at 100 ng/ml, 0.1 arbitrary unit (AU)/ml, and 0.004 AU/ml, respectively. Positive rate of AFP and DCP by the E-1023 kit and the high-sensitivity kit for HCC was 48%, 44%, and 57%, respectively. The positive rate by combination assay with AFP and DCP by the high-sensitivity kit increased up to 73%. There was no correlation between serum levels of AFP and those of plasma DCP. A significant correlation between tumor size and DCP levels was observed, but not with AFP. The postoperative disease-free survival rates of patients in the group with elevated levels of AFP and DCP were lower than those with normal levels of AFP and DCP. There were various patterns of change in the AFP and DCP levels at the time of recurrence compared with preoperative patterns. The combination assay of AFP and DCP levels is useful for the diagnosis, prognosis, and postoperative monitoring for recurrence of HCC.     

Protein induced by vitamin K absence or antagonist II as a prognostic marker in hepatocellular carcinoma. Comparison with alpha-fetoprotein

BACKGROUND: Protein induced by vitamin K absence or antagonist II (PIVKA-II) was widely used as a diagnostic marker for hepatocellular carcinoma (HCC), however, its prognostic value is unclear. The authors evaluated PIVKA-II clinicopathologically as a prognostic marker for HCC. METHODS: The relationship between pathologic prognostic factors and plasma PIVKA-II and alpha-fetoprotein (AFP) was investigated in 72 patients with resectable HCC measuring less than 6 cm in greatest dimension. RESULTS: PIVKA-II shows significantly lower sensitivity, but higher specificity than AFP, and the use of these two complementary markers appears to be useful in the diagnosis of HCC. The frequencies of intrahepatic metastasis, portal vein tumor thrombus, hepatic vein tumor thrombus, and capsular infiltration were significantly higher in patients with positive PIVKA-II than in those with negative-PIVKA-II, and the recurrence-free rate was significantly lower in patients with positive rather than with negative PIVKA-II. However, there were no significant differences between the patients who were AFP positive and those who were AFP negative in pathologic prognostic factors and the recurrence-free rate. From univariate and multivariate analyses, the authors find that PIVKA-II is one of the risk factors for recurrence of HCC after hepatectomy. CONCLUSIONS: PIVKA-II may be a useful marker for the prediction of intrahepatic spread and for the prognosis of HCC. In addition, PIVKA-II-positive patients, thus, need aggressive postoperative adjuvant therapy for undetectable residual tumors and careful postoperative monitoring to enable the early recognition of recurrence.     

Hepatoid carcinoma of the lung with production of alpha-fetoprotein and abnormal prothrombin: an autopsy case report

Alpha-fetoprotein (AFP) is a useful tumor marker for the diagnosis of hepatic and testicular tumors. Several cases of AFP-producing lung cancer have been reported. We present here a patient with AFP-producing primary lung carcinoma, which showed high values of serum AFP (100,000 ng/mL). The concanavalin A nonbinding fraction rate of AFP was 15%. Gross and microscopic features of the lung carcinoma bore a striking resemblance to those of hepatocellular carcinoma. According to the histologic classification of lung tumor, this case was large cell carcinoma with prominent hepatoid differentiation. Immunohistochemically, we detected AFP in the cytoplasm of the neoplastic cells. We also detected another useful tumor marker for the diagnosis of hepatocellular carcinoma, i.e., des-gamma-carboxy prothrombin (protein induced by vitamin K absence or the absence of antagonist-II [PIVKA-II]), in serum using an enzyme immunoassay and in tumor cells by immunohistochemical analysis.     

The usefulness of determining des-gamma-carboxy prothrombin by sensitive enzyme immunoassay in the early diagnosis of patients with hepatocellular carcinoma

BACKGROUND: Measurements of serum concentrations of des-gamma-carboxy prothrombin (DCP) are widely used for diagnosing hepatocellular carcinoma (HCC). However, the DCP is not always sensitive enough to detect small HCCs. In the current study, the authors investigated the usefulness of DCP in the early diagnosis of HCC, using a more sensitive enzyme immunoassay than is conventionally employed. METHODS: The authors examined 148 serum samples with DCP concentrations from a conventional assay of less than 100 mAU (arbitrary unit)/mL from 91 patients with HCC and 57 with cirrhosis. DCP concentrations were determined by a more sensitive enzyme immunoassay (ED-036 kit, Eisai Laboratory, Tokyo, Japan) with a minimal detection level of 10 mAU/mL. Ninety-one HCC patients had 43 solitary small HCCs (with a greatest dimension of less than 2 cm). Of these 43 HCCs, 12 were well differentiated. RESULTS: The mean serum concentration of DCP in HCC (48.3 +/- 24.3, mean +/- standard deviation [SD]) was higher than in cirrhosis (20.3 +/- 10.3); this difference was statistically significant. When the tentative cutoff level of 40 mAU/mL (almost corresponding to the mean value + 2SD in patients with cirrhosis) was used as the level of discriminating HCC from cirrhosis, 62% of patients (56 of 91) with HCC had DCP values above this level (sensitivity). However, only three patients with cirrhosis had higher DCP levels. Thus, the specificity of this test was 95% (54 of 57 patients). The total accuracy was 74% (56 + 54/91 + 57). Twenty-three of 43 solitary small HCCs (53%) had DCP values above the cutoff level. Furthermore, 7 of 12 (58%) small, well-differentiated HCCs less than 2 cm in greatest dimension had higher DCP values. CONCLUSIONS: The results of this study indicate that DCP determination by sensitive enzyme immunoassay is useful in the early diagnosis of HCC because a high specificity is maintained.     

Circulating vascular endothelial growth factor (VEGF) is a possible tumor marker for metastasis in human hepatocellular carcinoma

Vascular endothelial growth factor (VEGF) is closely related to angiogenesis in various human cancers. However, little is known of its circulating levels in hepatocellular carcinoma (HCC). We examined circulating VEGF levels in chronic liver disease to assess their clinical significance. Plasma VEGF concentrations were determined, by enzyme immunoassay, in patients with chronic hepatitis (CH; n = 36), liver cirrhosis (LC; n = 77), and HCC (n = 86) for a cross-sectional study. Plasma VEGF levels in healthy controls (n = 20) and CH, LC, and HCC patients were 17.7 +/- 5.4 (mean +/- SD), 30.6 +/- 22.8, 34.4 +/- 27.0, and 51.1 +/- 71.9 pg/ml, respectively. The levels were significantly elevated in the HCC group, compared with the control, CH, and LC groups. Plasma VEGF levels in stage I, II, III, IVA, and IVB HCC patients were 27.6 +/- 16.1, 26.5 +/- 13.7, 35.8 +/- 15.3, 45.4 +/- 39.4, and 103.1 +/- 123.2 pg/ml, respectively. The stage IVB patients with remote metastasis showed significantly marked elevation compared with the patients at the other stages. Platelet numbers were weakly correlated with plasma VEGF levels in the HCC group. Plasma VEGF level was highly elevated in patients with HCC, particularly those with metastatic disease. We consider that plasma VEGF is a possible tumor marker for metastasis of HCC. Circulating VEGF may be derived mainly from the large burden of tumor cells, and partly from platelets activated by the vascular invasion of HCC cells.     

Serum des-gamma-carboxyprothrombin level by a modified enzyme immunoassay method in hepatocellular carcinoma: clinical significance in small hepatocellular carcinoma

BACKGROUND/AIMS: In the diagnosis of hepatocellular carcinoma (HCC), serum des-gamma-carboxyprothrombin (DCP) is a useful tumor marker. The conventional immunoassays for measurement of DCP levels, however, are not sensitive enough to detect small HCC. Therefore, we intended to elevate the minimal detection level of DCP by a modified enzyme linked immunosorbent assay method. METHODOLOGY: This modified assay method is similar to the conventional enzyme linked immunosorbent assay (ELISA) method, but the first reaction occurs overnight. As a result, the minimal detection levels of DCP varied from 0.06 AU/ml, by the conventional method, to 0.008 AU/ml, by the modified method. Two hundred and twenty five serum samples from 100 patients with HCC, 75 with liver cirrhosis and 50 with chronic hepatitis were subjected to the present study. Simultaneous determinations of serum DCP by the modified assay and a-fetoprotein (AFP) levels were performed. RESULTS: Eighty five of 100 patients with HCC had increased DCP levels of more than 0.008 AU/ml. This method yielded a sensitivity of 85%, a specificity of 90% and a total accuracy value of 88%. In 27 patients with small HCC (less than 30 mm in diameter), 12 had elevated DCP levels, resulting in a sensitivity of 44%. When the modified DCP assay together with AFP measurement (more than 20 ng/ml) were introduced, the sensitivity was 67% in the 27 patients with small HCC. CONCLUSIONS: This modified ELISA method increased the sensitivity in patients with small HCC, and the combination assay of serum DCP and AFP levels was more useful for the early diagnosis of HCC.     

Circulating platelet-derived endothelial cell growth factor increases in hepatocellular carcinoma patients

BACKGROUND: Platelet-derived endothelial cell growth factor (PD-ECGF) is an angiogenic factor that is expressed in various cancer tissues. Little is known regarding plasma PD-ECGF levels in patients with chronic liver disease such as chronic hepatitis (CH), cirrhosis, and hepatocellular carcinoma (HCC) with cirrhosis. The expression of PD-ECGF in HCC tissues also remains to be clarified. METHODS: Plasma PD-ECGF levels in patients with chronic liver disease were determined with an enzyme-linked immunoadsorbent assay system using the mouse monoclonal antibodies specific to PD-ECGF. These were cross-sectionally compared among groups of normal persons, CH, cirrhosis, and HCC patients. The HCC patients were classified into two groups based on TNM stage: early and advanced stage disease groups. PD-ECGF expressions in HCC tissues were immunohistologically examined. RESULTS: The plasma PD-ECGF levels from the normal individuals and those with CH, cirrhosis, and HCC specimens were 4.2+/-0.5, 4.3+/-0.6, 4.6+/-1.1, and 6.0 +/-2.5 U/mL, respectively. The plasma PD-ECGF concentration was highest in HCC (P < 0.05). No significant difference was found among the normal subjects, CH, and cirrhosis specimens. Plasma PD-ECGF concentrations were significantly higher in the advanced stage disease HCC group compared with the early stage disease group (6.75+/-2.62 U/mL vs. 4.19+/-0.34 U/mL) (P < 0.05). Immunohistochemical expression of PD-ECGF in HCC cells increased significantly compared with normal liver cells (P < 0.05). CONCLUSIONS: Circulating PD-ECGF plasma level might be a new tumor marker for progression in patients with HCC. Immunohistological findings correspond to elevation of the plasma PD-ECGF in HCC patients. It is possible that increased production of PD-ECGF in HCC cells causes abundant neovascularization.     

Prospective study of nonsteroidal anti-inflammatory drugs and breast cancer

We have studied the feasibility of detecting tumor-associated aberrant p16 methylation in the circulation of patients with hepatocellular carcinoma (HCC). We extracted DNA from the tumor tissues and peripheral blood plasma or serum of 22 HCC patients. p16 methylation was found in 73% (16 of 22) of HCC tissues using methylation-specific PCR. Among the 16 cases with aberrant methylation in the tumor tissues, similar changes were also detected in the plasma/serum samples of 81% (13 of 16) of the cases. No methylated p16 sequences were detected in the peripheral plasma/serum of the six HCC cases without these changes in the tumor, in 38 patients with chronic hepatitis/cirrhosis, or in 10 healthy control subjects. These results suggest that circulating liver tumor DNA may be detected using tumor-associated DNA methylation changes. Because methylation abnormalities have been found in many other genes and tumor types, this approach may have implications for the noninvasive detection of a wide variety of cancers.     

Alpha feto-protein and albumin in ascitic fluid in hepatocellular carcinoma patients

Alpha-feto-protein (AFP) is the most popular tumor marker for hepatocellular carcinoma (HCC). It is used in diagnosis and follow up of cases by estimating its rise in the serum. The aim of this work is to study the value of estimating AFP in ascitic fluid of HCC patients with ascites. This work is a case control study on 32 patients, including 22 cases with ascites and HCC and 10 control group with ascites due to liver cirrhosis without HCC. The level of AFP was estimated in serum and in ascitic fluid by Radio-immuno assay RIA. The serum ascites albumin gradient (SAAG) was assessed by measuring albumin in all samples using bromocresole green dye binding. Guided aspiration liver biopsy and ascitic fluid cytology was done, stained with H & E. It was found that, AFP level in serum was elevated in 72.7% of HCC patients, and in ascitic fluid was elevated 63.6% HCC patients. Also, there was a highly significant, direct positive correlation between elevation of AFP in serum and in ascitic fluid (r = 0.778). No elevation of AFP in serum and in ascitic fluid was detected in control group. Ascitic fluid cytology showed malignant cells in one case only. SAAG was significantly lower in the HCC group 0.83 gm/dl than the control group 2.43 gm/dl (p-value < 0.001). Elevation of AFP in ascitic fluid is of high importance in evaluation of HCC, and is as significant as serum and runs parallel to it. Estimation of AFP in ascitic fluid is much more significant in evaluation of HCC cases than ascitic fluid cytology.     

The level of urokinase-type plasminogen activator receptor is increased in serum of ovarian cancer patients

Ascites and serum of patients with ovarian carcinoma contain a soluble form of urokinase-type plasminogen activator receptor (uPAR). We now report that pro-uPA-Sepharose-purified uPAR from ascites of patients with ovarian carcinoma is the full-length molecule missing the glycosyl-phosphatidylinositol anchor, as determined by its amino acid composition. We next examined the significance of determining serum soluble uPAR (suPAR) levels in ovarian cancer patients using a specific ELISA and compared the results with serum concentrations of CA-125, an established diagnostic marker. Serum from pre- and postoperative ovarian cancer patients was assayed for suPAR and CA-125. The majority of the patients with ovarian cancer had enhanced preoperative serum levels of suPAR compared with healthy controls, but suPAR concentrations decreased after operation. Although uPAR was associated with most ovarian carcinomas, it appeared to be a less specific indicator for ovarian cancer than CA-125. On the other hand, suPAR was more specific for other types of solid tumors. Moreover, we have observed some cases of ovarian cancer that showed increase of suPAR but not of CA-125. The prognostic significance of serum suPAR assay for survival of ovarian carcinoma patients was evaluated using Cox's proportional hazards analysis. Our preliminary data show that high preoperative levels of suPAR were associated with worse survival of the patients, whereas CA-125 had no prognostic implications. This is the first report evaluating the assay of serum suPAR levels in ovarian cancer and analyzing its value as a tumor or prognostic marker.     

Birthmarks to worry about. Cutaneous markers of dysraphism

CYFRA 21-1 is a fragment of cytokeratin 19 (CK 19). Four patients with large intrahepatic (or peripheral) cholangiocarcinoma (CC) and high serum levels of CYFRA 21-1 (normal, < or = 2 ng/ml) are reported. CYFRA 21-1 levels exceeded 9 ng/ml in all 4 patients. Carcinoembryonic antigen (CEA), was high in 1 (CEA; normal range, < or = 5.0 ng/ml) and carbohydrate antigen 19-9 (CA 19-9) was high in 3 (CA19-9; normal range, < or = 36 U/ml). We also measured serum levels of CYFRA 21-1 in 13 patients with hepatocellular carcinoma (HCC) more than 5 cm in diameter. Levels of CYFRA 21-1 exceeded 2 ng/ml in 9 of the HCC patients and were higher than 9 ng/ml in 2 of the HCC patients. Levels of alpha fetoprotein (AFP) and/or protein induced by vitamin K absence or antagonist II (PIVKA II) were elevated in all HCC patients (AFP, PIVKA II, respectively; normal range, < or = 10.0 ng/ml and < or = 0.1 AU/ml) CYFRA 21-1 levels were measured twice or three times during the clinical course in 2 CC patients and in 6 HCC patients, and increased gradually with tumor growth in the 2 CC patients and in 3 of the 6 HCC patients. Marked increases in serum CYFRA 21-1 levels in patients with large liver cancers, particularly in those with normal levels of AFP and PIVKA II, would suggest the existence of intrahepatic CC rather than HCC.     

Usefulness of telomerase activity in the diagnosis of small hepatocellular carcinoma

The diagnosis of small hepatocellular carcinoma (HCC) is sometimes difficult because of the similarity of the histological appearance with adjacent liver tissue. Recent advancement of the quantitative telomerase assay can diagnose small HCC effectively, and the positive rate surpasses those of alpha-fetoprotein and PIVKA-II. The application to a clinical field is, however, limited because the small nodules with the possibility of malignant phenotype tend to be treated easily with ethanol injection therapy without an additional biopsy for this assay only. Further analysis of telomerase related proteins might make it possible to visualize the activity in the tissue sections and expand the usefulness of telomerase as a diagnostic tool in routine clinical use.     

Quantitative determination of serum anti ribosomal-P protein antibody by enzyme immunoassay

An enzyme immunoassay for serum anti-ribosomal P protein antibodies (anti-P) is developed, using highly purified synthetic ribosomal P peptides of the carboxyl terminal 22 amino acid sequence conjugated to human serum albumin (HSA) as an antigen. Anti-P levels were determined by subtracting the nonspecific binding activities to HSA. The concentration of anti-P which produced half of the maximal absorbance at 492 nm (OD492) given by saturating concentrations of anti-P in the ELISA plate was defined as 1 U/ml. The anti-P values in the samples were determined by referring to a standard curve made from a standard serum containing anti-P. Serum anti-P levels in 34 normal individuals were 5.52 +/- 8.39 U/ml (mean +/- SD). Anti-P in sera from 45 patients with systemic lupus erythematosus (SLE), 24 patients with rheumatoid arthritis (RA) and 27 patients with Beh?et's disease were also analyzed. The values for serum anti-P in SLE, RA and Beh?et's disease groups were 251.04 +/- 843.07 U/ml, 5.97 +/- 15.18 U/ml, and 2.62 +/- 3.35 U/ml (mean +/- SD) respectively. The positive ratio for serum anti-P in SLE patients was significantly higher than that in patients with RA or Beh?et's disease (p < 0.05 as determined by chi-square test). These results indicate that quantitative determination of serum anti-P by our enzyme immunoassay is a successful tool for the diagnosis of SLE.     

Angiogenin expression and prognosis in primary breast carcinoma

Angiogenin is a protein originally isolated as an inducer of new blood vessel growth, and it has been reported to be an effective substrate for tumor cell adhesion. To understand the role of angiogenin in cancer progression, we evaluated the expression of angiogenin in 459 cases with primary breast carcinoma and in 40 benign breast specimens using an immunoassay. Higher angiogenin concentrations were observed in carcinomas in comparison with fibrocystic disease (mean, 17.3 versus 10.9 ng/mg; P = 0.008), but not with fibroadenomas. We selected 5 ng/mg cytosol protein of angiogenin as the normal cutoff for primary breast carcinoma. Eighty-eight percent of carcinomas expressed elevated angiogenin levels and 12% had low levels. We observed an association between elevated levels of angiogenin and low/ moderate histological grade (P = 0.001) and small tumor size (P = 0.026), but not with age, menopausal status, lymph node status, stage of disease, or hormonal receptor status. With a median follow-up of 31 months, breast cancer patients with elevated angiogenin levels had significantly longer disease-free survival (DFS) than patients with low angiogenin (log-rank, P = 0.003). This effect was equally observed in node-negative and node-positive cases. In a multivariate analysis of DFS, only angiogenin, tumor size, and histological grade showed statistical significance. A multivariate analysis of overall survival showed that angiogenin and tumor size were the only significant variables. Serum samples from the breast cancer patients at the time of surgery were available in 194 cases. We evaluated the levels of circulating angiogenin using the same immunoassay as in tumor tissue. Serum angiogenin levels were higher in cancer patients than in 40 healthy controls (mean, 401.2 versus 206.0 ng/ml; P < 0.0001). In breast cancer patients, we observed no correlation between the serum concentrations and the tissue levels of angiogenin (r = 0.115; P = 0.110). In addition, serum levels of angiogenin did not have a prognostic impact on the DFS of breast cancer patients (log-rank, P = 0.581). Our results indicate that elevated levels of tissue angiogenin, but not of circulating angiogenin, are a favorable prognostic factor in primary breast carcinoma, which is consistent with a role of angiogenin as a cancer cell substrate.     

Effects of dopaminergic drugs on food- and cocaine-maintained responding. IV: Continuous cocaine infusions

We modified and optimized a new microplate hybridization assay to detect the varciella-zoster virus (VZV) PCR product, and studied cerebrospinal fluid (CSF) samples of 287 patients with meningitis, encephalitis or other neurological diseases or symptoms. Specific antibodies to VZV and reference antigens were determined by enzyme immunoassay from serum and CSF, they were then compared with clinical findings and with the results obtained by VZV-PCR using different detection methods for VZV-specific amplified DNA. VZV DNA was found in the CSF of 25 patients using the microplate hybridization assay and chemiluminescence detection for amplified DNA. All 25 CSF samples were also positive in Southern blotting. Among the patients, 10 had chickenpox, 4 had shingles, and 11 had no rash at all. The detection rate of VZV-specific DNA by microplate hybridization was 30% higher than that obtained by conventional agarose gel electrophoresis. In most patients the diagnosis was confirmed by demonstrating specific intrathecal antibody production to VZV but not to other viruses. These results indicate the presence of VZV in the central nervous system (CNS) in many patients with chickenpox or shingles, and even in patients without a rash. The microplate hybridization assay based on chemiluminescence detection improves considerably the detection rate of the VZV-PCR product compared to agarose gel electrophoresis and will add to the list of recognized VZV infections in the CNS. It is especially useful in cases where there is no cutaneous manifestation.     

Establishment and evaluation of a new chemiluminescent enzyme immunoassay for carcinoembryonic antigen adapted to the fully automated ACCESS system

We have established a new chemiluminescent enzyme immunoassay for carcinoembryonic antigen (CEA), designated ACCESS CEA, which is adapted to the fully automated ACCESS immunoassay analyzer. The assay is based on a one step sandwich-type method using two monoclonal antibodies, one of which is immobilized on micrometer-size paramagnetic particles and the other is conjugated to alkaline phosphatase. Ten microliters of calibrators or sera are incubated for 5 minutes at 37 degrees C with the particles and with the alkaline phosphatase conjugate. The particles are then magnetically separated and washed to remove unbound components. Time needed to obtain the first result is less than 15 minutes. The assay range was 0.04-1000 micrograms/l of CEA, and the possible high-dose hook effect was prevented at CEA concentrations up to 100000 micrograms/l in this working range. The coefficient of variation (CV) for intra-assay precision was 3.0 to 4.7%, and inter-assay CV was 3.4 to 5.6%. The sample carryover was less than 0.001%. The analytical recovery ranged from 98 to 104% and a dilution linearity was demonstrated. No interference was detected in any sample with levels up to 300 mg/l for bilirubin, 12000 mg/l for haemoglobin, 50000 mg/l for human serum albumin, 8500 mg/l for triacylglycerol, and 500000 IU/l for rheumatoid factor. The ACCESS CEA assay also showed very homogeneous reactivity with purified CEA preparations from different tumours and could discriminate CEA from four CEA-related normal antigens tested. Serum samples (n = 362) from patients with malignant or non-malignant disease, as well as from healthy individuals, were analyzed by the ACCESS CEA assay and by the established IMx CEA assay. The CEA values determined by the ACCESS CEA assay were in good agreement with those determined by the IMx CEA assay, and the ACCESS CEA assay significantly increased the sensitivity and specificity of tumour diagnosis as compared with the IMx CEA assay.     

Erythropoietin in hepatocellular carcinoma

Hemopoietic alterations may occur during tumoral diseases, determining anemia. In most cases, serum EPO levels were lower than normal values. Hepatocellular carcinoma (HCC), one of the most frequent malignancies world-wide, is often characterized by mild anemia and increased serum EPO levels. We studied 30 HCC patients and 20 healthy subjects. We found that HCC patients presented higher serum EPO levels than healthy controls. In HCC patients, there was a significant inverse correlation between serum EPO levels and red blood cell count or hemoglobin levels. We postulated that the elevated serum EPO levels observed in these patients may be due to reduced hepatic clearance of EPO, and to the influence of cytokine-mediated inflammatory factors.     

Spatial and spectral dependence of the auditory periphery in the northern leopard frog

The transmembrane protein, transferrin receptor (TfR), exists in serum as a soluble form that lacks cytoplasmic and transmembrane domains (residues 1-100). The level of soluble TfR in serum is a sensitive indicator of total erythropoiesis and iron deficiency. This study revealed that the major part of soluble TfR was saturated by transferrin (Tf) in serum, forming a stable complex which was more immunoreactive than intact TfR. Thus, we proposed that serum soluble TfR should be measured as the TfR-Tf complex (TRC), using prepared TRC for assay standardization. We developed a new assay for TRC, employing antibody-coated latex agglutination nephelometry (LA). Rapid and reproducible measurements were achieved using an automated analyzer. The values obtained by this LA assay were closely correlated with those obtained by conventional enzyme immunoassay (r = 0.967). The mean level of TRC in 179 adult healthy subjects was 1.62 mg/l. Patients with iron-deficient anemia showed significantly higher TRC levels than the healthy subjects.