Higher Total Cell Counts Research Articles

小児における<I>Streptococcus pneumoniae</I>菌血症の臨床疫学的検討

From July 1999 to June 2004, we evaluated Streptococcus pneumoniae bacteremia in 40 children in Kamikawa and Soya Subprefectures in Hokkaido by obtaining the patient's information from 7 out of 9 hospitals in the area. The incidences of S. pneumoniae bacteremia in children aged < 2 years and < 5 years were 79.1 and 63.4. Median age was 19.6 months with a range from 4 months to 4 years. Thirty-one (77.5%) of the total were less than 2 years old. All of the children were admitted. The diagnoses were occult bacteremia in 12 patients, pneumonia or bronchitis in 11, pharyngitis in 7, pneumonia and acute otitis media in 5, acute otitis media in 3, orbital cellulitis in 1, and arthritis in 1. All of the patients had fever and temperatures and 35 (87.5%) of them were more than 39 degrees C. Ten patients had a febrile convulsion. Twenty-nine had a high total white blood cell counts (> 15,000/microg/ml) and 31 had positive CRP values (> 0.6 mg/dl) on admission. Meningitis and poor prognosis did not occur after occult bacteremia in our patients. We studied the susceptibility to penicillin G in 22 strains of S. pneumoniae isolated from the children. One and 18 strains were penicillin-resistant (MIC > or = 2.0 microg/ml) and intermediate (MIC 0.1-1.0 microg/ml).

Our Experience in the Flowcytometric DNA Analysis of Subretinal Fluid in the Regmatogenous Retinal Detachment and Proliferative Vitreoretinopathy

ABSTRACTStudies of the subretinal fluid in two groups of patients—with retinal detachment and retinal detachment and preoperative proliferative vitreoretinopathy to level C1 are done. By the possibilities of FC-DNA analysis, some parameters are used: total cell count and percentage of proliferating cells (percent of S-phase+G2/M-phase). The results, obtained in our study show a higher proliferative activity and a higher total cell count in the group with PVR. Additional studies with larger groups of patients are needed.

Vitrification versus programmable rate freezing of late stage murine embryos: a randomized comparison prior to application in clinical IVF

A prospective randomized trial was performed to compare post-thaw development of murine blastocysts following programmable rate freezing and two methods of vitrification. Frozen 2-cell murine embryos ( n = 429) thawed and cultured for 48 h, were randomly allocated by stage of development into four groups: control (not refrozen), programmable rate freezing (PR) in 0.25 ml straws, vitrification in flexible micropipettes by immersion in super-cooled (VSC) liquid nitrogen (LN 2), and vitrification in flexible micropipettes by immersion in LN 2 (VLN). Survival, developmental stage progression, presence or absence of an inner cell mass (ICM), and cell counts were recorded 24 h post-thaw. All measured outcomes were different between embryos from the control group and all freezing methods. Controlled-rate freezing resulted in the lowest total cell counts and fewest embryos with a distinct ICM. A higher percentage of embryos survived 24 h post-thaw, progressed to more advanced developmental stages and had higher total cell counts after VLN compared with PR. Moreover, fewer embryos, frozen by either PR or VSC, contained a detectable ICM compared with VLN. These data demonstrate that vitrification may be a better method for freezing murine blastocysts than PR, and may prove to be a superior method for freezing human blastocysts.

Application of Differential Inflammatory Cell Count as a Tool to Monitor Udder Health

A flow cytometric technique called differential inflammatory cell count was standardized by staining bovine peripheral blood leukocytes with a combination of DNA binding dyes SYBR green 1 and propidium iodide in water. Leukocytes were also stained with propidium iodide in detergent to determine total cell count. Differential inflammatory cell count assay was evaluated with individual quarter milk samples from 13 cows. Cows were sampled at weekly intervals for 3 wk and assayed for total cell count, mononuclear leukocyte count, and polymorphonuclear leukocyte count. Simultaneously, milk samples were evaluated by the conventional electronic somatic cell count (SCC) technique. Somatic cell count positively correlated with total cell count (r=0.9), mononuclear leukocyte count (r=0.8), and polymorphonuclear leukocyte count (r=0.89). Quarters with SCC>log10 5.4 had a higher total cell count, mononuclear leukocyte count, and polymorphonuclear leukocyte count and were more often culture positive compared with quarters with SCC>log10 5.4. Quarters that were culture positive on all three test occasions had a higher proportion of polymorphonuclear leukocytes (33 to 49%) compared with quarters that were culture negative on all three test occasions (17 to 25%). The findings of this study suggest that differential inflammatory cell count assay has the potential to evolve as a new technique for evaluation of udder health status.

The Effects of Compression Sutures On Filtering Blebs in Rabbit Eyes

To investigate the effect of compression sutures on filtering bleb cellularity in rabbit eyes. Six New Zealand rabbits had bilateral filtering surgery. In the study eye, on postoperative day 14 a 10-0 nylon suture was placed that compressed the bleb. Five-bromo-2'-deoxyuridine (BrdU) was injected intravenously on days 15, 16, and 18. On day 21 histologic sections of the blebs were obtained. The total cell count was compared to the number of actively dividing cells (marked by anti-BrdU antibody). Study eyes had higher total cell counts (P = .004) on postoperative day 21, but the proportion of proliferating cells was not significantly different (P = .11). In rabbit eyes, bleb compression sutures were associated with more cellular components in the bleb compared to control eyes, but did not induce a higher level of cellular proliferation.

Asthma and natural colds. Inflammatory indices in induced sputum: a feasibility study.

We examined the feasibility of using induced sputum to evaluate the airway inflammatory response to natural acute respiratory virus infections. We recruited eight asthmatics and nine healthy subjects on Day 4 of a cold. Viral infection was confirmed in six of the asthmatics (influenza A or B) and six of the healthy subjects (influenza A, rhinovirus, adenovirus, respiratory syncytial virus, and coronavirus). In the subjects with confirmed virus infection, five of the asthmatics had an objective exacerbation of asthma during the cold. Their sputum on Day 4 showed a high median total cell count of 19.7 x 10(6) cells/ml with a modest neutrophilia (58. 5%) and high levels of interleukin-8 (IL-8) (16,000 pg/ml), eosinophilic cationic protein (ECP) (1,880 microgram/L) and very high levels of fibrinogen (250 mg/L). In contrast, the proportion (1.3%) and absolute number of eosinophils was low. IL-2 levels were within the normal range, whereas IL-5 and interferon gamma were under the limit of detection of the assays. In the healthy subjects with a confirmed virus infection the sputum findings were qualitatively similar but significantly less prominent. Sputum IL-8 on Day 4 was strongly correlated with neutrophils (rs = 0.8, p < 0.001). This correlation was also significant when each group was analyzed separately. On Day 21 there was a fall in the absolute number of neutrophils and in ECP and fibrinogen levels in both groups. Similar results were found in the two asthmatic and three healthy subjects with a cold of comparable severity but in whom viral infection was not confirmed. We conclude that induced sputum examination can be used to study the effects of natural colds and influenza on the airways of the lungs. The results also suggest that natural colds, on Day 4, cause neutrophilic lower airway inflammation that is greater in asthmatics than in healthy subjects. The greater inflammatory response in asthmatics may be due to the changes associated with trivial eosinophilia or to the different viruses involved.

The Effect of α4β1-Integrin Binding Sequences of Fibronectin on Growth of Cells From Human Hematopoietic Progenitors

Highly regulated interactions between adhesion receptors on progenitor cells and their extracellular matrix ligands are essential for the control of hematopoiesis in bone marrow stroma. We have examined the relationship between alpha4beta1-integrin-mediated adhesion and growth of CD34(+) cells by assessing their adhesive and migratory patterns of proliferation in a mixture of hematopoietic growth factors in the presence of different recombinant fragments of the HepII/IIICS region of fibronectin. CD34(+) cells were isolated from cord blood and placed in culture wells containing serum-free medium and growth factors. Wells were precoated with either the H120 fragment of fibronectin, which contains three alpha4beta1-integrin binding sites, or the H0 fragment, which lacks the two highest affinity alpha4beta1 binding sequences. Proliferation of single cells of CD34(+)38(+)DR+ and CD34(+)38(-)DR+ phenotypes occurred in contact with the H120 substrate and was associated with migration. Larger numbers of cells were used to quantitate proliferative responses. Cells growing in wells coated with H120 formed attachments to the base of the wells throughout the culture period. Higher total cell counts were consistently found in wells coated with H120 compared with H0 and bovine serum albumin controls. The difference was first apparent at day 8 of culture and reached a maximum at days 11 through 13, when expansion with H120 was a mean of 1.8-fold higher than that seen with H0 (P</= .0001). The greatest expansion (2.25-fold) with H120 compared with H0 was seen when the growth factor concentrations were reduced to 1/16 of the standard levels (P </= .001). The increase in total cell numbers was not at the expense of CD34(+) cells as numbers of these were similar in H120 and control cultures. These results provide evidence for synergy between growth factors and integrins that may be relevant to understanding hematopoiesis in marrow stroma.

The Effect of α4β1-Integrin Binding Sequences of Fibronectin on Growth of Cells From Human Hematopoietic Progenitors

AbstractHighly regulated interactions between adhesion receptors on progenitor cells and their extracellular matrix ligands are essential for the control of hematopoiesis in bone marrow stroma. We have examined the relationship between α4β1-integrin–mediated adhesion and growth of CD34+cells by assessing their adhesive and migratory patterns of proliferation in a mixture of hematopoietic growth factors in the presence of different recombinant fragments of theHepII/IIICS region of fibronectin. CD34+cells were isolated from cord blood and placed in culture wells containing serum-free medium and growth factors. Wells were precoated with either the H120 fragment of fibronectin, which contains three α4β1-integrin binding sites, or the H0 fragment, which lacks the two highest affinity α4β1binding sequences. Proliferation of single cells of CD34+38+DR+and CD34+38−DR+phenotypes occurred in contact with the H120 substrate and was associated with migration. Larger numbers of cells were used to quantitate proliferative responses. Cells growing in wells coated with H120 formed attachments to the base of the wells throughout the culture period. Higher total cell counts were consistently found in wells coated with H120 compared with H0 and bovine serum albumin controls. The difference was first apparent at day 8 of culture and reached a maximum at days 11 through 13, when expansion with H120 was a mean of 1.8-fold higher than that seen with H0 (P≤ .0001). The greatest expansion (2.25-fold) with H120 compared with H0 was seen when the growth factor concentrations were reduced to 1/16 of the standard levels (P≤ .001). The increase in total cell numbers was not at the expense of CD34+cells as numbers of these were similar in H120 and control cultures. These results provide evidence for synergy between growth factors and integrins that may be relevant to understanding hematopoiesis in marrow stroma.

Comparison of methods for the concentration of bacterioplankton for in situ hybridization

Three approaches for concentrating stream bacterioplankton were compared for analysis by in situ hybridization: centrifugation; filtration onto a polymer membrane and transfer to a gel-coated slide; and filtration onto an inorganic filter disk. Stream bacterioplankton were hybridized with a species-specific oligonucleotide probe targeted for 23S rRNA of Burkholderia cepacia for analysis of variability among techniques. The inorganic filter technique yielded three to six times higher total cell counts and appeared to be effected less by interfering suspended particles and differences in site conditions than the other two concentration methods. Hybridization of samples with minimum cell loss yielded different, and presumably more accurate, estimates of the relative abundance of B. cepacia than the other methods.

Computed tomography in miliary tuberculosis: Comparison with plain films, bronchoalveolar lavage, pulmonary functions and gas exchange

Computed tomography (CT) of the chest, pulmonary function tests, bronchoalveolar lavage (BAL) and arterial blood gas analysis were performed in 26 patients with non-HIV miliary tuberculosis (MTB). CT was repeated after treatment in 11 patients. Nodular lesions were characteristically seen on CT. CT showed discrete and fine nodules in five patients in whom the lesions appeared to be larger than miliary on chest X-rays. Coalescing nodular lesions were noted on chest X-rays (n = 7) and CT (n = 18). Consolidation (n = 6), cavitation (n = 4), fibrosis (n = 9) and air trapping (n = 14) were detected on CT only. During follow up, air trapping increased (n = 14) and in some patients it appeared for the first time (n = 2). Lymph node enlargement and calcification were seen on both chest X-rays (n = 9 and n = 3, respectively) and CT (n = 12 and n = 7, respectively). Pleural involvement was also seen in chest X-rays (n = 4) and CT (n = 5). Total lung capacity was higher in patients with a chest X-ray score > 10. Similarly a higher total cell count in BAL fluid was observed in patients with a CT score > 10. It is concluded from this study that CT is superior to chest X-rays in detecting nodular lesions, lymphadenopathy and air trapping in patients with MTB.

Gestational Age and Cell Viability Determine the Effect of Frozen Storage on Human Fetal Hematopoietic Progenitor Cell Preparations

We have assessed hematopoietic progenitor cell preparations (including CD34-positive stem cells) obtained from human fetal liver at 6-17 weeks of gestational age for total cell numbers, viability and the ability to tolerate (frozen) storage. Hematopoietic cell preparations obtained from the 16-to 17-week gestational age range had the highest total cell count and the greatest proportion of CD34-positive stem cells. However, these preparations were insufficiently robust to withstand the freeze/thaw protocol required. Cells obtained from the 13- to 15-week gestational age range showed optimal post-thaw viability and it is suggested that these cell preparations are the most applicable for in utero transplantation.

Haemolytic-uraemic syndrome in childhood: surveillance and case-control studies in Italy. Italian HUS Study Group.

Seventy-six cases of haemolytic-uraemic syndrome (HUS) were collected over a 4-year period during a surveillance and case-control study. The annual incidence of 0.2 per 100,000 children aged 0-14 years is lower than in other countries; 34% had no prodromal diarrhoea. Evidence for verocytotoxin-producing Escherichia coli (VTEC) infection was found in 72% of patients and 3% of controls; 88% of patients with bloody diarrhoea, 67% with non-bloody diarrhoea and 55% without diarrhoea were VTEC positive. Seventy-three percent of patients had creatinine clearance > or = 80 ml/min per 1.73 m2, normal blood pressure, no proteinuria and haematuria < 2+ after 1 year of follow-up. One patient died and none had non-renal sequelae. VTEC positivity was significantly correlated with a good outcome, while the absence of diarrhoea and a high total white blood cell count at onset were not predictors of a bad outcome. Household contacts of HUS patients had diarrhoea more frequently than those of the control group, supporting the hypothesis of person-to-person transmission of VTEC infection.

Role of the complete blood count in detecting occult focal bacterial infection in the young febrile child

Previous studies of the value of the complete blood count (CBC) in distinguishing viral from bacterial infection in young febrile children have failed to exclude children with clinically evident bacterial infection and thus have inflated the positive predictive value of the test for occult focal infection. We prospectively studied 2492 children 3–24 months of age who presented to a children's hospital emergency department between March 1989 and August 1990 with fever (⩾ 38.0°C) of acute (⩽ 4 days) onset but no evident bacterial focus of infection, 433 (17.4%) of whom received a CBC. We also carried out an 8-year retrospective analysis to estimate prior, or pre-test, probabilities (prevalences) and examine CBC results for rare occult bacterial infections (meningitis, osteomyelitis, and septic arthritis). Estimated prior probabilities for the four most common categories of infection that can be diagnosed at the initial visit were: non-pneumonitic viral infection, 88.6% in boys and 86.0% in girls; pneumonia, 8.5% in both sexes; urinary tract infection (UTI), 3.0% in boys and 5.5% in girls; and bacterial meningitis, 0.0066% in both sexes. The likelihood (sensitivity) of a total white blood cell (WBC) count ⩾ 15,000/mm 3 was 25.5, 64.5, 62.5, and 50.0% for viral infection, pneumonia, UTI, and meningitis, respectively. Among children with a high total white blood cell count, neither a total polymorphonuclear count ⩾ 10,000/mm 3 nor a band count ⩾ 500/mm 3 was associated with significantly elevated likelihoods for occult pneumonia or UTI, a finding confirmed by multiple logistic regression analysis. Based on the prior probabilities and likelihoods of WBC ⩾ 15,000/mm 3 for each diagnosis, the posterior probabilities (positive predictive values) were: viral infection, 75.3% in boys and 70.8% in girls; pneumonia, 18.5% and 17.9%; UTI, 6.2% and 11.3%; and bacterial meningitis, 0.01% in both sexes. Thus a high WBC count approximately doubles the overall probability of occult focal bacterial infection. Even in the face of a high WBC count and “shift to the left”, however, a viral diagnosis remains far more likely. Given the rarity of occult bacterial meningitis, the apparent lack of morbidity associated with gross underdetection of occult pneumonia, and the existence of a less invasive, more specific test (the urinalysis) for the diagnosis of UTI, clinicians should critically re-examine their use of the CBC in the young febrile child.

Rabies in horses: 21 cases (1970-1990)

Summary The records of 21 horses with rabies were reviewed. Results of fluorescent antibody testing for rabies antigen in brain tissue were positive in each case. According to the histories, 5 of the horses had been vaccinated for rabies between 4 to 24 months prior to the onset of the clinical signs. Bite wounds were not observed on any of the horses, and exposure to a suspected rabid animal was witnessed in only 5 cases. Clinical signs of disease at the time of initial examination included ataxia and paresis of the hindquarters (9/21, 43%), lameness (5/21, 24%), recumbency (3/21, 14%), pharyngeal paralysis (2/21, 10%), and colic (2/21, 10%). The major clinical signs observed over the course of hospitalization included recumbency (21/21; 100%), hyperesthesia (17/21; 81%), loss of tail and anal sphincter tone (12/21; 57%), fever (11/21; 52%), and ataxia and paresis of the hindquarters (11/21; 52%). Mean survival time after the onset of clinical signs was 4.47 days (range, 1 to 7 days). Supportive treatment, given to 9 horses, had no effect on survival time and did not correlate with the detection of negri bodies at necropsy. Cerebrospinal fluid (csf) was obtained from 6 horses and was determined to be abnormal in 5. The most common abnormality was a slightly high total cell count (5/6), with a predominance of lymphocytes (4/6). The csf total protein concentration was high in only 2 horses. At necropsy, there was gross evidence of diffuse brain edema, meningeal congestion, and focal areas of hemorrhage in 5 horses (24%). The major histologic findings included diffuse perivascular cuffing with leukocytes (predominantly lymphocytes) in the meninges and neural parenchyma (14/21; 67%), neuronal degeneration and neuronaphagia (11/21; 52%), gliosis (9/21; 43%), and malacia of the gray matter of the spinal cord (6/21; 28%). Negri bodies were not identified in brain tissue of 11 horses (53%). Horses that survived 4 or more days after the onset of clinical signs were significantly (P &lt; 0.025) more likely to have negri bodies in the neural tissues.

Cytologic, microbiologic, and biochemical analysis of bronchoalveolar lavage fluid obtained from 24 healthy cats

Summary Twenty-four healthy cats underwent bronchoscopy and bronchoalveolar lavage to determine the normal cytologic environment of the lower respiratory tract of cats. Initial screening to ensure the health of the study population included complete histories, physical examinations, thoracic radiography, cbc, serologic tests for feline leukemia virus, feline immunodeficiency virus, and occult heartworm, and sugar and Baermann fecal flotation. In 18 cats, protected catheter brush samples of airway secretions from the lavaged lung segment were taken for culture of aerobic and anaerobic bacteria and mycoplasma. Bronchial lavage fluid (5 sequential 10-ml aliquots of normal saline solution) was pooled and filtered with cotton gauze. The unspun sample was used for determination of a total nucleated cell count. Lavage fluid was cytocentrifuged and 500 cells/slide were scored for determination of the cellular differential. Activity of lactate dehydrogenase and concentrations of total protein and IgG within the supernatant were measured, and assays were performed to detect the presence of IgA and IgM. Complete histologic evaluation of the lavaged lung of each of 6 random-source cats was performed after differential cell counting revealed 18% eosinophils within bronchoalveolar lavage fluid recovered from this group. Alveolar macrophages were the predominant cells encountered; however, a quarter of all cells recovered were eosinophils. A significant relationship was not found between the abundance of eosinophils in the lavage fluid, and either isolation of aerobic bacteria, high total nucleated cell counts, total protein concentrations, or activity of lactate dehydrogenase. Histologic evaluation of the lungs of 5 of 6 random-source cats revealed normal lungs in 2 cats, and minimal abnormal change in 3 others. Evaluation of the lungs from 1 random source cat revealed acute, mild eosinophilic bronchiolitis. We conclude that large numbers of eosinophils may be retrieved from the bronchoalveolar lavage fluid of healthy cats.

Use of flow cytometry to extend and improve in vivo determinations of microvessel hematocrit and cell flux

The use of fluorescent-erythrocyte tracer methods for estimating microvascular variables has been extended and improved by using flow cytometry. With cell tracer methods, the precision of estimates of cell flux, hematocrit, etc. is dependent on the labeled-cell fraction ( p). In larger arterioles, high cell flux and the requirement to identify each labeled cell mandate the use of very low labeled-cell fractions. Precise microvascular estimates require high total cell counts in the estimation of p. This is not practical to do manually, but can be accomplished by flow cytometry. Determinations of p in experimental samples were made by both flow cytometry and microscopy. These values were compared to each other and to calculated values. In the range 0.0045 < p < 0.075, where manual counting statistics give CV( p) < 0.12, counts by microscopy and flow cytometry were not significantly different. This confirms that flow cytometry identifies the same cell population as seen in vivo. Flow cytometry counts will resolve p > 0.00001 for rhodamine-labeled-cell fractions and p > 0.0002 for fluorescein-labeled-cell fractions. Rhodamine-labeled-cell fraction samples analyzed when fresh or after 1–3 weeks storage in RPMI 1640 media (GIBCO) gave p values which agreed to within 4%. We identify the use of rhodamine-labeled cells as a simple yet powerful method of rare-event analysis for many in vivo applications.

Clinical findings and prognostic factors in chronic myeloid leukemias.

Ninety-one previously untreated patients with chronic myeloid leukemia admitted to three Stockholm hospitals 1973-1978 were studied. There were 49 men and 42 women with a mean age of 56 years (range 15-93). Sixty-five patients were Philadelphia chromosome (Ph1) positive and 17 were Ph1 negative (mean age 51 and 70 years, respectively). After a mean observation time of 5.2 years, 64 patients had deceased, 45 of them in blast transformation. A low hemoglobin value and a high total blast cell count at diagnosis were associated with a poor prognosis in the Ph1 positive group. Other routine clinical and laboratory variables were of subordinate prognostic importance. Early splenectomy in 15 Ph1 positive patients did not improve survival. Median survival from diagnosis was 38 months for Ph1 positive patients as compared to 12 months for the Ph1 negative group.

Use of white cell counts to select units of whole blood for granulocyte preparation.

Multiple variables that are easily determined, including donor white cell count, were studied for possible value in selecting single units of whole blood for isolation of granulocytes. Whole blood units selected on the basis of total white cell count were shown to have a 78 percent greater granulocyte content than randomly selected units (3.0 X 10(9) granulocytes/unit vs. 1.7 X 10(9) granulocytes/unit, p less than .001). White cell counts determined on 5-hour-old segments of whole blood were demonstrated to have a high coefficient of correlation with white cell counts determined on freshly drawn EDTA specimens (r = 0.918) and fresh segments of whole blood (r = 0.926). We conclude that yields of granulocytes from single units of whole blood stored for up to 5 hours at room temperature can be increased by selecting units with high total white cell counts performed on blood unit segments.

Tissue mast cells in breast cancer.

The total number of mast cells and the number of such cells observed within and at the periphery of invasive breast cancers from 424 patients enrolled in protocol 4 of the National Surgical Adjuvant Breast Project were correlated with 38 other pathologic and 6 clinical features. High total mast cell counts as well as those within and at the periphery of the cancers were found to be significantly (p less than or equal to .05) associated with a patient age less than 50 years and the degree of tumor lymphoid cell reaction. The latter has also been found to be related to young age and other pathologic characteristics related to mast cell content. This suggests that the mast cells may simply represent another cell type of this reactive change. No differences in 10 year disease-free survival were detected in patients without mast cells and those exhibiting varying numbers of such cells. This information indicates that identifiable mast cells do not represent a prognostic pathologic discriminant in patients with breast cancer. However, this does not unequivocally exclude a role of mast cell secretory products, since only intact and not degranulated or disrupted forms of these cells can be counted.

Synovial Fluid Crystals

Synovial fluid was aspirated from the Joints of unselected groups of patients suffering from rheumatoid arthritis (30), osteoarthritis (34), pyrophosphate arthropathy (25) and gout (six). Specially selected patients with osteoarthritis (10) and other miscellaneous forms of arthropathy (six) were also Included. Total and differential cell counts were performed, and the fluids were examined by polarized light microscopy and analytical electron microscopy to determine crystal content. fluids from patients with rheumatoid arthritis and gout had a higher total cell count, and greater proportion of polymorphonuclear cells. There was no difference in the cell content in patients with osteoarthritis and chronic pyrophosphate arthropathy. Osteoarthritic fluids containing crystals did not have a significantly different cell count from those without. Polarized light microscopy was confirmed as a good technique for differentiating urate from pyrophosphate crystals. However, pyrophosphate crystals varied greatly in appearance, and were occasionally too small to be visualized. Crystals thought to be brushite, formed in some fluids after aspiration, causing confusion on polarized light examinations, and other unidentified birefringent material was often seen. Analytical and scanning electron microscopy revealed a wide variation in the morphology and elemental content of synovial fluid crystals. Hydroxyapatite crystals were identified in nine out of 34 unselected osteoarthrltlc fluids, in 10 selected cases, and six with synovitis of unknown cause. Hydroxyapatite was seen in combination with pyro phosphate in six cases, and was the only crystal identified in one case of ‘pyrophosphate’ nrthropathy. Small pyrophosphate crystals, not seen with the light microscope, were identified in two cases. Other crystalline particles containing calcium and phosphorus were seen in some cases, but could not be identified. No crystals were identified in rheumatoid arthritis fluids. Crystal phagocytosis was visualized using scanning electron microscopy. It is concluded that hydroxyapatite crystals are commonly present in synovial fluids in chronic arthritis, with or without pyrophosphate, and that a range of other calcium phosphate salts remain to be identified.